What Is a Solo 401(k)? Rules and Contribution Limits

A Solo 401(k) is the retirement plan a self-employed person builds for a business of one, and it solves a specific frustration: you know a workplace 401(k) is a powerful account, and you no longer have a workplace. The plan goes by several names, including individual 401(k) and one-participant 401(k), and all of them describe the same thing, a real 401(k) plan whose only participants are the owner and possibly a spouse. What makes it interesting is not that it copies a workplace plan but that it lets one person play both roles in it at once.

This explainer walks through what a Solo 401(k) is and how it behaves: who qualifies and what disqualifies you, the two-hat structure that stacks an employee deferral on top of an employer contribution, how that employer piece is computed differently for a sole proprietor and an S-corp owner, the Roth bucket, the loan provision, the deadlines that trip people up, the filing obligation that appears once the plan grows, and an honest head-to-head against the SEP IRA. Every dollar figure here is illustrative and chosen to show structure, because contribution limits change every year. Our explainer on what a SEP IRA is covers the simpler employer-only alternative, and our overview of retirement account types puts both in context. Model what a contribution becomes with the calculator as you read.

What a Solo 401(k) actually is

A Solo 401(k) is a qualified retirement plan under the same section of the tax code that governs the 401(k) your employed friends have at work. The only structural difference is who is in it. A conventional 401(k) is sponsored by a company for a workforce, with testing rules and disclosure obligations designed to stop the plan from favoring owners over rank-and-file staff. A Solo 401(k) has no rank and file, so most of that machinery falls away and what remains is the useful part: high contribution room, a choice between pre-tax and Roth treatment, and tax-sheltered growth.

The plan is sponsored by your business, whatever legal form that business takes, and you participate in it as the business’s only employee. Money you put in belongs to you, is invested in whatever the provider’s menu allows, and grows without the annual tax drag a brokerage account carries. The account is not a special product a bank sells so much as a plan you adopt and then fund. That framing matters, because it explains why there is a plan document to sign and, eventually, a filing to make.

Who is eligible for a Solo 401(k)

Two conditions define eligibility, and both have to hold. First, you need self-employment income from a business you own. That covers a full-time freelancer, a consultant, a contractor, a single-member LLC, a partner in a partnership, and an owner-employee of an S-corporation, and it also covers someone running a genuine side business while holding down a regular job. Second, the business must have no full-time employees other than you and, if you have one, your spouse.

The spouse exception is not a technicality; it is a real planning feature, because a spouse who works in the business and is paid by it can participate in the same plan with their own deferral and their own employer contribution. That effectively doubles the room a household can use, which is why so many two-person businesses adopt one. Nothing about the size of your income affects eligibility. A modest side business qualifies just as a high-earning consultancy does, though the amount you can actually put in scales with what the business earns. Confirm the current definitions before adopting a plan, since the rules describing a covered employee have been revised over time.

What disqualifies you from a Solo 401(k)

The disqualifying event is almost always the same one: hiring a full-time employee who meets the plan’s eligibility conditions. Once that happens, the plan is no longer a one-participant plan, and it becomes a regular 401(k) subject to the coverage and nondiscrimination testing that the solo version escapes. That is not the end of the world, but it changes the cost and administration profile substantially, and it is why growing businesses often plan the transition rather than discovering it.

Several categories of worker can generally be excluded from that head count under a plan’s terms, which is why a business with seasonal or limited-hours help may still qualify. Independent contractors are not employees, so paying a contractor does not by itself break eligibility, but misclassifying an employee as a contractor is a separate and serious problem that can unravel the plan later. Long-term part-time workers have been brought into 401(k) coverage by legislative changes in recent years, which narrows a gap that used to be wider. Because these boundaries have moved and continue to move, confirm the current employee-coverage rules before assuming your help does not count.

The two hats that make a Solo 401(k) powerful

Here is the mechanism that explains everything else. In a workplace 401(k), two different parties can put money in: the employee, who elects to defer part of their pay, and the employer, who may add a match or a profit-sharing contribution. Our explainer on what a 401(k) match is covers that second party from the employed side. In a Solo 401(k), both parties are you. You wear the employee hat and make a salary deferral out of your own compensation, and then you wear the employer hat and make a profit-sharing contribution out of the business.

Those two contributions have separate caps, and they stack. That is the entire reason a Solo 401(k) usually beats an employer-only plan at moderate income. An employer-only plan gives you one of the two pieces; the Solo 401(k) gives you both. At a low or moderate income the deferral piece can be a very large share of what you earn, so the stacking effect is proportionally biggest exactly where people assume a self-employed plan would be weakest. At very high income the picture converges, because the overall annual cap eventually binds regardless of which plan you use.

The employee deferral, explained

The employee half is a salary deferral: you elect to divert part of your compensation into the plan instead of taking it in cash. It is capped at a flat dollar amount that the IRS publishes and adjusts, and that amount does not scale with your income, though you cannot defer more compensation than you actually have. In this explainer the illustrative deferral limit is $20,000, a round number chosen to make the arithmetic legible and deliberately not a current figure.

Two features of this cap matter more than the number itself. It is a per-person limit rather than a per-plan one, so deferrals into a workplace 401(k) at a day job and deferrals into your own Solo 401(k) draw on the same annual bucket. And it is generally an in-year election, because you are deferring compensation you have not yet received, which is why the deferral half of a Solo 401(k) has to be set up and elected during the working year rather than at tax time. Confirm the current dollar limit and the current election timing before you plan around either.

The employer profit-sharing contribution, explained

The employer half works completely differently. It is not a flat dollar amount but a percentage of compensation, commonly cited as up to about 25 percent, and it is discretionary, meaning you decide each year whether to make it and how large it should be. Because it is a percentage, it scales directly with what the business earns: a strong year produces a large employer contribution and a lean year can produce none at all, which suits the reality of self-employment income far better than a fixed commitment would.

There is a second ceiling on this piece that is easy to miss. The compensation that the percentage applies to is itself capped, so income above a threshold the IRS sets does not increase the employer contribution at all. In this explainer’s illustrative arithmetic that compensation cap is $300,000, which at a 20 percent effective rate produces an employer piece of $60,000, exactly the illustrative overall cap used throughout. That alignment is deliberate, chosen so the numbers hang together. The actual thresholds move every year, so confirm the current percentage cap and the current compensation ceiling before relying on either.

Sole proprietor vs S-corp: why the employer math differs

The percentage is the same idea in both cases, but the base it applies to is not, and that is where most confusion lives. For an owner-employee of an S-corporation, “compensation” means the W-2 wages the corporation pays you. The up-to-25-percent figure applies straightforwardly to that wage number. Distributions the S-corp makes to you beyond your wages are not compensation for this purpose, so paying yourself a small wage and taking the rest as distributions shrinks your retirement contribution room even though your total take-home is unchanged.

For a sole proprietor or a single-member LLC taxed as one, there are no wages. “Compensation” means net earnings from self-employment, which starts from business profit and is then reduced by an adjustment the IRS specifies and by the deductible portion of self-employment tax you owe. Because the contribution itself also enters that calculation, the headline 25 percent works out to a lower effective rate on the pre-contribution profit figure, commonly cited at roughly 20 percent. This explainer uses that 20 percent effective rate for sole proprietors and 25 percent of wages for S-corp owners. The precise worksheet and the self-employment tax mechanics are set out in IRS materials, so run your own figures with a tax professional.

The overall annual additions cap

Above both pieces sits a third limit: an overall cap on annual additions to the plan for any one participant, covering the employee deferral, the employer contribution, and anything else that lands in the account for the year. Whatever the two halves come to, their sum cannot exceed this ceiling. In this explainer the illustrative overall cap is $60,000, again a round teaching figure rather than a current limit.

The practical effect is that the two-piece advantage of a Solo 401(k) is largest in the middle of the income range and disappears at the top. At a modest income the deferral is a big absolute addition over what a percentage alone would allow. As income climbs, the employer percentage grows until deferral plus employer contribution meets the overall cap, and from that point extra income adds nothing. Using the illustrative numbers, a sole proprietor with $200,000 of net profit reaches $20,000 of deferral plus $40,000 of employer contribution, which is exactly the $60,000 ceiling. Confirm the current overall cap, since it is one of the numbers that changes annually.

Catch-up contributions for savers over 50

Retirement plans generally allow an additional catch-up contribution once a saver reaches a specified age, and a Solo 401(k) is no exception. The catch-up attaches to the employee deferral, not to the employer piece, so it is an extra amount you can defer beyond the standard dollar cap. Structurally it also sits outside the overall annual additions ceiling, which means an older saver’s total can exceed the headline cap by the catch-up amount rather than being squeezed under it.

Rules in this area have been in motion. Legislation in recent years has adjusted both the size of the catch-up for certain age bands and the tax treatment of catch-up contributions for higher earners, with phase-in dates that have shifted. That combination makes this the single worst area to rely on remembered numbers. This explainer uses an illustrative catch-up of $6,000 purely to keep the worked example concrete. If you are near or past the qualifying age, confirm the current catch-up amount, the age bands, and the current treatment with the IRS or a qualified tax professional before planning around it.

Illustrative Solo 401(k) contribution by income

Because one half of the contribution is a flat dollar amount and the other is a percentage, the total does something a single-piece plan never does: it starts high relative to income and then flattens. The chart below traces an illustrative sole proprietor under the catch-up age, using this explainer’s illustrative $20,000 deferral limit, a 20 percent effective employer rate, and the illustrative $60,000 overall cap. Every figure is a teaching illustration, not a current limit.

Read the shape rather than the numbers. At $50,000 of profit, a plan with only an employer piece would allow roughly $10,000, while the Solo 401(k) allows about $30,000, three times as much. At $200,000 the employer piece alone would allow about $40,000 against the Solo 401(k)’s $60,000, a much narrower edge, and beyond that point the gap keeps closing as the cap binds. This is the honest version of the claim that a Solo 401(k) beats a SEP: it is a moderate-income advantage that fades at the top. Put your own contribution into the calculator and watch what steady saving compounds into.

Where an older saver’s contribution comes from

The stacking is easiest to see when you break a single year’s total into its parts. Take an illustrative sole proprietor past the catch-up age with $100,000 of net profit. The employee deferral is the illustrative $20,000, the catch-up adds an illustrative $6,000, and the employer piece at a 20 percent effective rate adds another $20,000, for an illustrative total of $46,000. The stacked bar below shows how that total splits.

The split is the argument in miniature. More than half of this illustrative saver’s contribution comes from the employee side, which an employer-only plan does not have at all. Shift the profit figure up and the employer slice grows until it dominates; shift it down and the deferral slice takes over almost entirely. Your own split depends on your profit, your age, and the current limits, so treat these shares as a demonstration of the structure rather than a target. Our walkthrough on how much to contribute to a 401(k) works through the same deferral decision from the employed side.

The Roth option inside a Solo 401(k)

Most mainstream Solo 401(k) plan documents let you designate the employee salary deferral as Roth. The trade is the familiar one: you give up the deduction today in exchange for qualified withdrawals that come out tax-free in retirement, and the money grows untaxed in between either way. For a self-employed saver whose income swings from year to year, the ability to choose per year is genuinely useful, because a lean year is a natural year to pay tax at a low rate and bank Roth dollars.

Two caveats deserve emphasis. Provider support is not universal, and a low-cost brokerage’s standard plan document may or may not include a Roth bucket, so confirm the feature before adopting rather than after. And Roth dollars inside a 401(k) follow the plan’s own qualification rules, which are not identical to a Roth IRA’s, particularly on the timing of when withdrawals become qualified. Our walkthrough on Roth IRA vs traditional IRA develops the underlying tax-timing choice in full. Rules governing Roth treatment of employer contributions have also been changing, so confirm current law and your provider’s actual offering.

Pre-tax or Roth: how to think about the split

The honest answer is that nobody knows their future tax rate, so the decision is a judgment about probabilities rather than a calculation with a right answer. The general principle is that pre-tax wins if your rate in retirement is lower than your rate now, Roth wins if it is higher, and the two are equivalent if the rates match. Beyond that, the case for Roth strengthens if you expect your business to grow, if you value the absence of required distributions from a Roth account later in life, or simply if you prefer certainty about what your balance is actually worth.

A practical compromise many self-employed savers use is to split rather than choose, sending part of the deferral to each bucket so the outcome does not hinge on a single forecast. Note one structural asymmetry: the employer profit-sharing piece has traditionally been a pre-tax contribution, so a plan that offers Roth deferrals may still deliver a pre-tax employer contribution, which means a “Roth” Solo 401(k) is often mixed rather than pure. Confirm what your plan document permits and consider running the choice past a tax professional who can see your whole picture.

The Solo 401(k) loan provision

A feature that no IRA and no SEP IRA offers is the participant loan. Many Solo 401(k) plan documents permit you to borrow a portion of your vested balance and repay it, with interest, back into your own account on a fixed schedule. Because you are paying interest to yourself rather than to a lender, the arrangement feels appealing, and for a business owner facing a cash squeeze it can be a genuine option that avoids a taxable distribution.

The mechanics carry real risk, and it is worth being plain about it. The maximum you can borrow, the repayment period, and the payment frequency are governed by rules the IRS sets, and a loan that misses payments or otherwise falls out of compliance can be treated as a distribution, which brings ordinary income tax and, below the qualifying age, a possible early-withdrawal penalty. Money on loan is also not invested, so it stops compounding. Many low-cost brokerage plan documents simply omit the loan feature, which is often the single reason a saver picks a more expensive provider. Confirm the current loan limits and whether your plan actually permits one.

How to open a Solo 401(k)

The practical sequence is short. You obtain an employer identification number for the business if you do not already have one, choose a provider, adopt a written plan document that provider supplies, open the account or accounts under the plan, make a written deferral election for the year, and then fund the contributions. Most large brokerages offer a Solo 401(k) with a standardized plan document at no setup charge, and specialist administrators offer more customized documents for a fee when you want features the standard document lacks.

The plan document is the step people underestimate. It is the legal instrument that creates the plan, and its terms decide whether you get a Roth bucket, whether loans are available, whether rollovers in are accepted, and how the deferral election is recorded. A free standardized document is perfectly adequate for a saver who wants a plain pre-tax and Roth plan with index funds; it is not adequate if you want features it does not contain. Our walkthrough on how to open a Roth IRA covers the fund-selection habits that apply here too. Confirm current setup requirements before you begin.

Deadlines: establishing the plan and funding it

Deadlines are where Solo 401(k) enthusiasm most often collides with the calendar, because the two contribution pieces run on different clocks. The employee salary deferral is an election about compensation you have not yet received, so it generally has to be elected during the year in which you earn the income. Someone who decides in the spring that a Solo 401(k) would have been a good idea for the previous year typically finds the deferral half unavailable for that year, which is exactly the piece that made the plan attractive.

The employer profit-sharing contribution is far more forgiving and can generally be funded later, up to your business tax filing deadline including extensions, once you actually know your profit. The rules on when the plan itself must be established have been relaxed by legislation in recent years, so older advice you may have read is not reliable. Our explainer on the IRA contribution deadline shows how differently the individual accounts behave here. Confirm the current establishment and funding deadlines for your business structure with the IRS or a tax professional.

The annual filing obligation

A one-participant 401(k) is exempt from most of the reporting a company plan carries, but not from all of it forever. Once the plan’s total assets pass a threshold the IRS sets, the plan generally has to file a short annual information return for one-participant plans. A final return is also generally required in the year the plan is terminated and the assets are distributed, regardless of size.

This is the recurring administrative cost that a SEP IRA does not have, and it is the honest counterweight to the Solo 401(k)’s extra contribution room. The form itself is short and many savers complete it without help, but missing it is expensive, because penalties for late filing of plan returns accrue per day and can become severe. This explainer uses an illustrative threshold of a quarter of a million dollars in plan assets purely to make the concept concrete; the real figure and the filing mechanics are set by the IRS and change, so confirm the current threshold, form, and due date, and consider having a tax professional handle the first one.

Solo 401(k) vs SEP IRA, head to head

These are the two plans a self-employed saver realistically chooses between, so it is worth putting them side by side on the features that actually decide it. Both are employer-sponsored plans for the self-employed, both shelter far more than a personal IRA, and both invest in ordinary market funds. Everything below is a general characterization, and the specific limits and thresholds are set by the IRS and change, so confirm the current details rather than relying on any single row.

Reading down the columns, the Solo 401(k) trades administration for room and features, and the SEP trades room and features for near-zero administration and a decision you can make after the year has ended. Our explainer on what a SEP IRA is covers the right-hand column in full detail.

Which plan fits which situation

Rather than declaring a winner, it helps to name the situations plainly. The Solo 401(k) is usually the better fit if your self-employment profit is modest to moderate and you want to shelter a large share of it, because the deferral piece is where the advantage lives. It is also the better fit if you want Roth dollars inside the plan, if you want the loan feature available, or if you have a spouse in the business whose own deferral doubles the household’s room.

The SEP IRA is usually the better fit if you value simplicity above all, if you did not think about retirement contributions until tax season and need a plan you can still fund for last year, if your income is high enough that both plans hit the overall cap anyway, or if you may hire employees and would rather have a plan that accommodates them. A third situation deserves naming: if your business is very new and profit is uncertain, the SEP’s after-the-fact decision is worth real money. None of this is advice about your circumstances, and a tax professional who can see your full picture is worth consulting before you commit.

Adding a spouse to the plan

The spouse provision is the most underused feature of the Solo 401(k). A spouse who genuinely works in the business and is compensated by it can participate as a second employee without breaking one-participant status. That means a second full employee deferral, a second catch-up if they qualify by age, and an employer profit-sharing contribution computed on their compensation, all inside the same plan with the same document and the same provider.

The word doing the work in that paragraph is “genuinely”. The spouse has to actually perform work and be paid reasonable compensation for it, and paying a spouse purely to unlock contribution room is not a strategy the rules support. For an S-corp this means real W-2 wages; for a sole proprietorship the arrangement is more complicated and depends on how the business is structured. Adding a spouse also affects the plan-asset total that drives the filing threshold, since the plan’s combined assets are what count. Confirm the current requirements for compensating a spouse and the resulting filing obligations with a tax professional.

If you also have a job with a workplace 401(k)

This is the most common real-world complication, and the rule that governs it is simple to state and easy to violate by accident. The employee deferral limit is a per-person annual limit, not a per-plan one. Deferrals into your employer’s 401(k) and deferrals into your own Solo 401(k) draw from the same bucket, and no payroll department is tracking the combined figure for you. Exceeding it creates an excess deferral that has to be corrected, with tax consequences if it is not caught in time.

The employer side behaves differently and this is where the real opportunity sits. Employer contributions are generally applied per unrelated employer, so a match at your day job and a profit-sharing contribution from your own business are separate. Someone who already maxes their workplace deferral can still open a Solo 401(k) for a side business and use the employer piece, adding room that would otherwise be unavailable. Our comparison of IRA vs 401(k) covers how the workplace account interacts with individual accounts. Confirm the current aggregation rules before running two plans at once.

Investments, fees, and what providers differ on

Once the plan exists, the investing decision is ordinary. A Solo 401(k) at a major brokerage typically opens the full menu of stocks, bonds, mutual funds, and exchange-traded funds, which is more choice than most workplace plans offer, and low-cost broad index funds remain the default answer for a saver who does not want to pick individual holdings. There is no employer fund lineup constraining you and no recordkeeping fee layered on top of the funds at most large providers.

What providers actually differ on is the plan document and the service around it. Free standardized documents from big brokerages typically cover pre-tax and Roth deferrals and accept rollovers in, but may omit loans and may not permit alternative assets. Specialist administrators charge a setup fee and an annual fee for documents that allow more, sometimes including loans and non-traditional investments. Paying for features you will never use is a straightforward waste, and choosing a free document that lacks the one feature you needed is the more annoying error. Our note on whether you need an advisor for a 401(k) covers when paying for help is worth it.

Withdrawals, penalties, and required distributions

Pre-tax money in a Solo 401(k) behaves like pre-tax money in any 401(k): withdrawals are taxed as ordinary income, and money taken out before a qualifying age can trigger an additional early-withdrawal penalty on top of the tax, subject to a list of exceptions the IRS defines. Roth money in the plan follows the plan’s Roth qualification rules, which turn on both an age condition and a holding-period condition, so a Roth balance is not automatically accessible tax-free just because it is Roth.

Traditional-style balances are also subject to required minimum distributions once you reach a specified age, meaning the deferral eventually has to unwind and be taxed. The specific ages, the exception list, and the required-distribution rules have all been changed by legislation more than once in recent years, so any number remembered from a few years ago is likely to be wrong. Our walkthrough on 401(k) withdrawal rules covers the mechanics in more depth. Confirm the current ages, penalties, and exceptions before planning any withdrawal.

Rolling money in and out of a Solo 401(k)

Most Solo 401(k) plan documents accept rollovers in, which makes the plan a useful consolidation point for old workplace balances scattered across former employers. Rolling an old 401(k) into your Solo 401(k) keeps the money in a plan rather than an IRA, which matters for one specific reason: a balance sitting in a pre-tax IRA can complicate a backdoor Roth contribution, while the same balance inside a 401(k) generally does not. Our walkthrough on how to roll over a 401(k) covers the mechanics of moving the money without triggering tax.

Rolling money out is also possible, though while the plan is active and you are still self-employed, distribution options are limited by the plan’s terms. When the business closes or you take a job elsewhere, the plan is typically terminated and the balance rolled to an IRA or a new employer’s plan, and that termination year carries its own final filing. Watch the direct-versus-indirect distinction on any rollover, since an indirect rollover involves withholding and a strict redeposit window. Confirm the current rollover rules and your plan document’s terms before moving anything.

Common mistakes with a Solo 401(k)

The most expensive mistake is missing the deferral election window, because it silently removes the larger half of the contribution for that year and leaves you with roughly what a SEP would have allowed anyway. The second is an S-corp owner paying themselves a minimal wage to reduce payroll tax, then discovering that the employer contribution is a percentage of that same small wage, so the tax saving on one side cost more retirement room on the other.

Three more come up repeatedly. Forgetting the annual filing once plan assets cross the threshold, which is easy to miss because nothing prompts you and the penalties accrue daily. Double-counting the deferral across a day-job plan and a Solo 401(k), which creates an excess that must be corrected. And adopting a free plan document without checking whether it includes the Roth bucket or the loan provision you specifically wanted, which is only discoverable after you need the feature. None of these are exotic; they are all calendar and paperwork errors, which is precisely why a checklist and a tax professional earn their keep.

A worked example: one consultant’s Solo 401(k)

Make it concrete with an illustrative consultant named Maya. She is a sole proprietor with no employees and an illustrative $100,000 of net self-employment profit for the year. Wearing the employee hat, she elects to defer the illustrative $20,000 limit, an election she makes during the working year rather than at tax time. Wearing the employer hat, she makes a profit-sharing contribution at the roughly 20 percent effective rate for a sole proprietor, which is another $20,000. Her illustrative total is $40,000, comfortably under the illustrative $60,000 overall cap.

The comparison is what makes the point. An employer-only plan at the same profit would have allowed roughly the $20,000 employer piece alone, so the two-hat structure adds about $20,000 of sheltered room in this illustrative year. If Maya were past the catch-up age, an illustrative $6,000 catch-up would lift her total to $46,000, the split shown in the stacked bar above. If she instead ran an S-corp paying herself $60,000 in wages, the employer piece would be 25 percent of those wages, about $15,000, plus the same deferral, showing how the structure changes the answer. All figures are illustrative; confirm the current limits.

Using a calculator to size a Solo 401(k) contribution

A calculator earns its place here in one specific way: it turns a contribution into a balance, which is the number that actually motivates saving. Enter what you can realistically put away each year, an assumed return, and a horizon, and you see how tax-sheltered compounding turns a stream of contributions into something much larger than their sum. The calculator on this page runs that compound-growth math, and it is worth running twice, once with the employer piece alone and once with the full two-hat contribution, to see what the stacking is really worth over decades.

What no calculator can settle is your actual contribution limit. That depends on your business structure, your finished profit or wage figure, the current deferral cap, the current percentage and compensation caps, the current overall ceiling, and whether a catch-up applies to you. Those inputs come from your own numbers and from current IRS figures, ideally checked by a tax professional. Treat any output as illustrative, vary the assumptions to see how sensitive the result is, and remember that a plan you actually fund every year beats a larger plan you fund once.

The bottom line

A Solo 401(k) is the self-employed saver’s version of the workplace plan, and its defining trick is that one person occupies both seats: you defer part of your compensation as the employee, then contribute a share of profit as the employer, and the two stack under one annual ceiling. That structure is why it usually shelters more than an employer-only plan at moderate income, and why the advantage narrows at the top once the overall cap binds. The price is real administration: a plan document, a deferral election that must happen during the working year, and an annual filing once plan assets grow past a threshold. Weigh that honestly against the SEP IRA, which gives up the deferral and the Roth bucket in exchange for a plan you can open and fund after the year has closed. Every dollar figure here is a teaching illustration, because the deferral limit, the catch-up, the compensation cap, the overall ceiling, and the filing threshold all change from year to year, so confirm the current numbers with the IRS or a qualified tax professional before you act. Then put your own contribution into the calculator and see what steady funding becomes.

This explainer is educational only and is not tax, legal, investment, or financial advice, and it is not a substitute for reading the current IRS materials or speaking with someone who knows your situation. The $20,000 deferral, the $6,000 catch-up, the $60,000 overall annual additions ceiling, the $300,000 compensation cap, the quarter-of-a-million-dollar filing threshold, the 20 percent sole-proprietor effective rate, the 25 percent figure applied to S-corp wages, and every profit and contribution amount in the charts, the table, and Maya’s example were chosen as round teaching numbers to keep the arithmetic legible. They are not current limits and are not intended to resemble any particular year’s figures. Contribution caps, catch-up amounts and their tax treatment, compensation ceilings, plan-establishment and deferral-election deadlines, filing thresholds, early-withdrawal penalties and their exceptions, and required-distribution ages are set by law and revised regularly, several of them annually. The self-employment tax mechanics and the net-earnings worksheet that convert business profit into the compensation figure a contribution is based on are described here by mechanism rather than by percentage, precisely because the details deserve a worksheet and not a memory. Plan documents differ, so the Roth bucket, the loan provision, rollover acceptance, and the available investments depend on the provider you choose. Investing involves risk, including the possible loss of principal, and no projection is a promise. Before adopting a plan, choosing between a Solo 401(k) and a SEP IRA, compensating a spouse, running a Solo 401(k) alongside a workplace plan, taking a plan loan, or planning any withdrawal, confirm the current rules and consult a qualified professional such as a tax advisor and a fee-only fiduciary planner.

Edited by Hamza Hai, MBA · Editor

Hamza Hai is the editor of SumLoft. She holds an MBA and reviews the site's articles against our editorial standards, checking that every figure is labelled for what it is, that nothing is presented as verified fact without a source the reader can check, and that the writing stays useful to a non-specialist.

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