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Solo 401(k)

Solo 401(k) Contribution Calculator

The solo 401(k) has the highest ceiling of any plan a freelancer can open — and it is the one where the two halves compete. Your deferral and your business's contribution come out of the same $72,000, not on top of each other. This page runs the worksheet the IRS publishes for self-employed people and shows which limit is the one actually stopping you.

Prepared for the 2026 tax year.

The rate is not the rate. A plan that says 25% does not give you 25% of profit: Publication 560 divides it by one plus itself, so 25% becomes 20%. Applying the stated rate overstates the contribution by a quarter.

Schedule C line 31 — your profit after business expenses, before any retirement contribution.
Sets the catch-up, and which one. Ages 60 to 63 get a larger figure than 50 to 59 — that is the SECURE 2.0 rule, not a mistake.
The employee half. Leave it at the maximum unless you have already deferred into another 401(k) this year — that limit is per person, not per plan.
The rate in your plan document for the employer contribution, before Publication 560 reduces it.
The Form 7206 figure, if you claim one. It reduces the profit before the contribution rate is applied, so a larger premium means a smaller retirement contribution.

Enter your profit and your age. The page runs the IRS worksheet and tells you the maximum you can contribute, which part of it is the deferral and which is the business contribution — and which of the three limits decided it.

Maximum contribution $0
Your deferral $0
Business contribution $0
Catch-up $0
What limited the business part —
Room left under the $72,000 ceiling $0

Which plan suits you better? A SEP IRA takes nothing from the deferral side but has no catch-up and no Roth option. The SEP vs Solo 401(k) Calculator runs both plans on the same profit and shows where the gap closes.

Paying for health cover out of the same profit? The Self-Employed Health Insurance Calculator shows what the premium is worth, and how it shrinks the room left here.

Where these figures come from

Contribution ceiling
Elective deferral
Compensation limit
$360,000 ·
Order of the limits
IRS Publication 560, Chapter 5 — Deduction Worksheet for Self-Employed, steps 1 to 21
Reduced rate
Plan rate ÷ (1 + plan rate) · Pub. 560, Rate Worksheet for the Self-Employed
Verified
4 October 2026
How this is worked out

Every line comes from the worksheet in Publication 560, chapter 5, in the publication's own order. The steps below are the ones that change the answer; the full worksheet has twenty-one.

Net earnings
Net profit − one-half of self-employment tax − health insurance deduction
Pub. 560 (2025), steps 1 to 3
The health insurance deduction comes off first. It reduces the base the contribution rate applies to, so the two deductions compete for the same profit — the same interaction the Form 7206 page describes from the other side.
Self-employed rate
Plan contribution rate ÷ (1 + plan contribution rate)
Pub. 560 (2025), Rate Worksheet for Self-Employed
A 25% plan gives 20%, not 25%. 0.25 ÷ 1.25 = 0.20. The publication states the result is rounded to at least three decimal places, and its worked example writes 0.078 for 0.078341 — so it rounds down, which claims the smaller deduction.
The business contribution
Smallest of: (net earnings × reduced rate), (25% of $360,000), ($72,000 − deferral), or half of compensation after the deferral
Pub. 560 (2025), steps 5 to 13
Four limits, and the smallest wins. On a low profit the fourth is what binds — half of what remains after the deferral — which is why the business contribution can be zero on a profit that is not zero.
The whole contribution
Business contribution + deferral + catch-up
Pub. 560 (2025), step 19

The formulas are shown as the authority defines them, in its own terms — the arithmetic is not copyrightable and the rates are public-domain US government material. What these lines cannot tell you is where your figures came from; that is what the table above is for.

Two pools, one ceiling

The phrase people search for is "how much can I put in a solo 401(k)", and the honest answer is a range, not a figure. $72,000 is the ceiling for 2026, and it is shared between what you defer as the employee and what the business contributes as the employer. Fill one and you have less room for the other.

And the order matters, which is the part most pages get wrong. Taking the deferral does not just subtract from the ceiling — it also reduces compensation, and the employer's deduction is capped at half of what remains. So a large deferral can shrink the business contribution by more than its own size. The worksheet handles this in steps 9 to 13; a page that only subtracts the deferral from $72,000 will overstate the answer.

Where the 25% goes

A plan document that states a 25% contribution does not produce 25% of profit. Publication 560 has you divide the rate by one plus itself first — 0.25 becomes 0.20 — because the contribution is paid out of the profit it is measured against. Applying 25% directly overstates the contribution by a quarter, and the error grows with income.

Frequently asked questions

How much can I contribute to a solo 401(k) in 2026?

$72,000 in total, plus an $8,000 catch-up if you are 50 or over — but both halves come out of that figure. Your deferral can be up to $24,500, and the business can add up to 25% of compensation, and the two together cannot pass $72,000. Most people who ask the question are thinking of them as separate allowances, and that is the misunderstanding this page exists to fix.

Why does the business contribution get smaller when I defer more?

Because the deferral reduces compensation, and the business limit is measured on compensation. Step 10 of the worksheet takes the deferral off the $72,000 ceiling; step 12 then limits the business part to one-half of the compensation left after the deferral. At lower profits that half is the binding limit, so a full deferral can push the business contribution toward zero. Deferring does not cost you a dollar for dollar reduction — it can cost more.

I am 61. Which catch-up applies to me?

The larger one — $11,250 rather than $8,000, and it applies for the four years you are 60, 61, 62 or 63. This is a SECURE 2.0 provision, and it is why the age field on this page separates 60 to 63 from 50 to 59: they are different figures, and a page with a single "over 50" checkbox gets one of them wrong.

Is the catch-up inside the $72,000?

No — it sits on top. The IRS states that total contributions to a participant's account, not counting catch-up contributions, cannot exceed the overall limit. So the true maximum for someone of 61 is $72,000 plus $11,250, and this page shows the catch-up separately for that reason.

Do I also have a 401(k) where I am employed?

Then your deferral limit is already partly used, and this calculator cannot know by how much. The IRS is explicit that the limit on elective deferrals is by person, not by plan — a business owner who also participates in an employer's 401(k) must consider the limit for all deferrals made during the year. Enter the amount you have already deferred in the deferral field, not the $24,500 maximum, and the worksheet will work from the right figure.

How late can I open the plan and still contribute for 2026?

The plan must exist by 31 December 2026, but the contribution can wait until your return is due. That is a real difference from a SEP, which can be opened as late as the filing deadline including extensions. The deferral election is the part with the earlier deadline, and for a sole proprietor with no employees the two are often treated together — which is why the answer is not simply "by the deadline".

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