Solo 401(k) Contribution Calculator (2026)
Enter your Schedule C profit, your age band and any 401(k) deferrals made at a job, and see the most you can put into a one-participant 401(k) this year — employee deferral and employer share separately — and what it saves.
Federal 2026 data checked against the official publications, last on 2026-09-05 Runs in your browser — nothing you type is sent anywhere, not even when you reload or share the link No sign-up Methodology and data status
- Maximum solo 401(k) contribution
- $43,087
- At the maximum, tax saved
- $5,243
- Effective saving
- 12.2%
- A SEP-IRA would allow
- $18,587
| How the maximum is built | |
|---|---|
| Net profit | $100,000 |
| Less the deductible half of self-employment tax | −$7,065 |
| Net earnings (the contribution base) | $92,935 |
| Employee elective deferral: up to $24,500, and no more than net earnings | $24,500 |
| Employer contribution: 20.0% of net earnings (25% of compensation after the contribution), and no more than half of what is left after the deferral | $18,587 |
| Maximum solo 401(k) contribution | $43,087 |
| What contributing $43,087 does | Without | With |
|---|---|---|
| Self-employment tax | $14,130 | $14,130 |
| Adjusted gross income | $92,935 | $49,848 |
| Qualified business income deduction | $15,367 | $6,750 |
| Federal taxable income | $61,468 | $26,999 |
| Federal income tax after credits | $8,235 | $2,992 |
| Tax saved (federal) | $5,243 · 12.2% of the contribution |
The contribution reduces adjusted gross income and, through Reg. §1.199A-3, qualified business income; it does not change self-employment tax, which is computed on profit before the deduction. A solo 401(k) contribution cannot exceed the figure above on this profit. What caps the employer share here is the 25%-of-compensation deduction limit of §404(a)(3), which for a self-employed person works out to 20% of net earnings. The figure is a contribution ceiling and the tax saving assumes it all goes in pre-tax. Designated Roth contributions count against the same limits but are not deducted, so they reduce the saving without changing the maximum.
How the solo 401(k) maximum is computed
A one-participant 401(k) takes two contributions from the same person wearing two hats. As the employee, the owner may defer up to $24,500 of compensation (§402(g)(1)), but not more than net earnings; the limit is per person, so deferrals made at a job during the year use it up. As the employer, the business may contribute 25% of compensation, which for a self-employed person works out to 20% of net earnings after the deductible half of self-employment tax (§401(c)(2), §404(a)(8)). Together the two may not exceed the §415(c) annual additions limit, $72,000 for 2026, or net earnings.
Catch-up contributions sit on top of the §415(c) dollar limit: $8,000 for a participant aged 50 or over at the end of the year (§414(v)(2)(B)(i)), or $11,250 for one who reaches 60, 61, 62 or 63 during the year (§414(v)(2)(E)(i)). They are outside the annual additions limit (§414(v)(3)(A)) but still capped at compensation less the year's other deferrals (§414(v)(2)(A)(ii)), so at low profit a catch-up can be worth nothing.
Why a small profit allows less than 20% plus the deferral
Section 415(c)(1)(B) also caps annual additions at 100% of compensation, and for a self-employed person compensation is net earnings after the employer contribution (§401(c)(2)(A)(v)) with elective deferrals added back (§415(c)(3)(D)). Written out, that is deferral + employer ≤ net earnings − employer, so the employer contribution is limited to half of what is left after the deferral — the step Publication 560's Deduction Worksheet performs at lines 11 and 12. Each dollar of employer money costs two dollars of headroom while a dollar of deferral costs one, which is why the worksheet takes the deferral first, and why below about $24,500 of net earnings an employer contribution actually lowers the total you can put in.
Maximums by profit level (2026, no deferrals elsewhere)
The deferral and employer columns are the amounts that go in together, not two separate ceilings; they add to the total.
| Net profit | Net earnings | Deferral | Employer | Total, under 50 | Age 50+ | Age 60–63 | SEP-IRA, for comparison |
|---|---|---|---|---|---|---|---|
| $25,000 | $23,234 | $23,234 | $0 | $23,234 | $23,234 | $23,234 | $4,647 |
| $32,000 | $29,739 | $24,500 | $2,620 | $27,120 | $29,739 | $29,739 | $5,948 |
| $50,000 | $46,468 | $24,500 | $9,294 | $33,794 | $41,794 | $45,044 | $9,294 |
| $100,000 | $92,935 | $24,500 | $18,587 | $43,087 | $51,087 | $54,337 | $18,587 |
| $200,000 | $185,883 | $24,500 | $37,177 | $61,677 | $69,677 | $72,927 | $37,177 |
| $400,000 | $383,205 | $24,500 | $47,500 | $72,000 | $80,000 | $83,250 | $72,000 |
Notice the first two rows: the employer contribution is small or zero, and the deferral carries the whole total. That is the compensation limit described above at work. Once net earnings pass about $40,833 — roughly $43,900 of profit — the limit stops binding and the familiar "deferral plus 20%" arithmetic applies. At large profits the employer share alone reaches the $72,000 cap and the plan converges with a SEP-IRA, except for the catch-ups. The trade-offs are set out in SEP-IRA vs solo 401(k).
Deadlines
Elective deferrals normally have to be elected by December 31 of the year they are for. For a plan's first year, a sole proprietor with no employees may adopt the plan after year-end and still make deferrals for that year, provided both the adoption and the deferrals happen by the return's original due date — April 15, 2027 for 2026 — without regard to extensions (SECURE 2.0 Act §317). The employer contribution can be made up to the extended due date. Once plan assets exceed $250,000 an annual Form 5500-EZ is required.
How these figures were checked
The solo 401(k) maximum follows Publication 560's "Deduction Worksheet for Self-Employed" step by step, for one sole proprietor with no wages from a job, no other business, a plan contribution rate of 25% and pre-tax contributions. The cases below are worked from Schedule C profit through Schedule SE to the worksheet's total, and they are the same cases the site's tests check.
The rules and where they come from
- Net earnings (worksheet steps 1–3): profit less the deductible half of self-employment tax, from Schedule SE lines 4a–13 — 92.35% of profit, no tax below $400 of that amount (§1402(b)(2)), Social Security on earnings up to the $184,500 2026 wage base.
- Employer contribution (steps 4–7): 20% of net earnings, the rate table's figure for a 25% plan (§404(a)(8)(D)), on no more than $360,000 of compensation (§401(a)(17)).
- Elective deferral (steps 9 and 15): up to $24,500 (§402(g)(1)), less deferrals made in any other employer's plan that year, and never more than net earnings.
- Compensation test (steps 11–13): the employer share may not exceed half of what is left after the deferral (§415(c)(1)(B), with compensation measured as in §401(c)(2) and deferrals added back under §415(c)(3)(D)).
- Dollar limit (steps 8 and 10): $72,000 of annual additions (§415(c)(1)(A)).
- Catch-up (steps 16–18): $8,000 from age 50, or $11,250 at ages 60–63 (§414(v)), outside the dollar limit but still within compensation.
- 2026 dollar amounts: IRS Notice 2025-67, and the Social Security Administration's wage base.
Worked examples (2026)
| Case | Net profit | Half of SE tax (step 2) | Net earnings (step 3) | Deferral (step 15) | Employer (step 13) | Catch-up (step 18) | Maximum |
|---|---|---|---|---|---|---|---|
| Net earnings under $400: no SE tax, so the whole profit can be deferred | $400 | $0.00 | $400.00 | $400.00 | $0.00 | $0.00 | $400.00 |
| The 100%-of-compensation test binds (steps 11–12) | $25,000 | $1,766.19 | $23,233.80 | $23,233.80 | $0.00 | $0.00 | $23,233.80 |
| The 100%-of-compensation test binds (steps 11–12) | $32,000 | $2,260.73 | $29,739.27 | $24,500.00 | $2,619.63 | $0.00 | $27,119.63 |
| Deferral plus the full 20% employer share | $50,000 | $3,532.39 | $46,467.61 | $24,500.00 | $9,293.52 | $0.00 | $33,793.52 |
| Age-50 catch-up of up to $8,000 on top (steps 16–18) | $100,000 | $7,064.78 | $92,935.22 | $24,500.00 | $18,587.04 | $8,000.00 | $51,087.04 |
| Age 60–63 catch-up of up to $11,250 on top (steps 16–18) | $100,000 | $7,064.78 | $92,935.22 | $24,500.00 | $18,587.04 | $11,250.00 | $54,337.04 |
| $10,000 already deferred at a job reduces the deferral (step 9) | $100,000 | $7,064.78 | $92,935.22 | $14,500.00 | $18,587.04 | $0.00 | $33,087.04 |
| The $72,000 §415(c) dollar limit binds (steps 8 and 10) | $400,000 | $16,795.30 | $383,204.70 | $24,500.00 | $47,500.00 | $8,000.00 | $80,000.00 |
Half of SE tax is shown to the cent, but it is carried exactly; only the worksheet's results are rounded, and always down, because a maximum must never round up. Subtracting the rounded figure by hand can therefore differ from net earnings by a cent. The IRS worksheet itself works in whole dollars, so a hand-completed return can differ by a dollar or two.
What the checks are
- The rules were read from the primary documents twice, in separate software-agent sessions, and every difference was resolved from the document; an adversarial pass then recomputed cases by hand. The maintainer reviewed each reconciliation. See the editorial policy.
- Every case in the table above and on the SEP-IRA page (10 cases in all) is also computed by a separate program written directly from the Schedule SE lines and the worksheet steps, for tax years 2025 and 2026. The two agree to the cent, and the site is not built while any of these tests fails.
- Publication 560's own example — $200,000 of 2025 profit with a $13,596 self-employment tax deduction — is reproduced: the engine gives $13,596.35.
- Nothing here has been reviewed by a CPA, enrolled agent or attorney.
What this does not cover
- Designated Roth contributions: they count against the same limits but are not deductible (worksheet steps 20–21), so the maximum contribution shown is not a deduction figure for Roth money.
- Wages from a job share the Social Security wage base, so together with large self-employment earnings they can reduce SE tax. The calculator above accounts for them; the worked examples assume none.
- Employees, partnerships, S corporations, more than one business or plan, and related employers treated as one.
- Whether you can open or fund the plan: eligibility, plan documents and deadlines are not tested.
Errors found and fixed
Until 9 September 2026 the solo 401(k) maximum ignored the 100%-of-compensation test, so for 2026 profits between about $26,400 and $43,900 it was too high. Two smaller fixes followed the same day: the parts are now settled to the cent in order, so they add to the total exactly, and a catch-up already made in another employer's plan now reduces the room here. Each is dated in the corrections log.
Common questions
Can I make Roth contributions?
Most solo 401(k) providers offer Roth elective deferrals, and since 2023 the law also permits Roth employer contributions. Roth amounts count against the same limits but do not reduce this year's income; the calculator's tax-saved figure assumes pre-tax contributions.
I have a 401(k) at my job. How does that interact?
Enter the regular deferrals you have made there, and any catch-up separately. Both are one amount per person across every employer (§402(g) for the deferral, §414(v) with Treas. Reg. §1.402(g)-2 for the catch-up), so the solo plan's room shrinks by what you have already used. The employer share of the solo plan is unaffected, and each plan has its own §415(c) limit.
What if my spouse works in the business?
A spouse who earns compensation from the business can participate in the same plan with their own deferral and employer share, computed on their own earnings; the plan stays a one-participant plan for filing purposes.