No. If you’re a sole proprietor, or a single-member LLC taxed like one, a Solo 401(k) lowers your income tax but not your self-employment tax. The contribution is a deduction that comes after self-employment tax has already been figured, so that tax stays where it was.
An S corporation owner is in a different position, and that’s covered further down.
Why the contribution doesn’t touch it
Two forms do the work, and the order matters.
Self-employment tax is figured on Schedule SE. It starts from your net profit on Schedule C, takes 92.35% of it, and applies 15.3% (12.4% for Social Security up to the annual wage base and 2.9% for Medicare), as the IRS explains. Our guide to how self-employment tax is calculated walks through it.
Your Solo 401(k) contribution isn’t on Schedule C. It’s an adjustment to income on Schedule 1 of Form 1040, on the line for self-employed SEP, SIMPLE and qualified plans (Schedule 1, and Publication 560 for the worksheet). It lowers your adjusted gross income, which is what income tax is figured from. Schedule SE has already used the Schedule C profit by then (Schedule SE instructions).
Even the deductible half of self-employment tax works this way. The IRS notes that deduction doesn’t affect your net earnings or your self-employment tax either.
Example: $80,000 of profit, with and without a contribution
Take a single filer under 50 with $80,000 of Schedule C net profit and no other income, using 2026 figures. The most they can put into a Solo 401(k) is $39,370: a $24,500 employee deferral plus a $14,870 employer contribution, from the site’s retirement contribution calculator. We ran the same profit through the site’s tax code twice, once with no contribution and once with that maximum.
| No contribution | $39,370 contribution | |
|---|---|---|
| Schedule C net profit | $80,000 | $80,000 |
| Self-employment tax | $11,304 | $11,304 |
| Deductible half of SE tax | $5,652 | $5,652 |
| Solo 401(k) contribution (Schedule 1) | $0 | $39,370 |
| Adjusted gross income | $74,348 | $34,978 |
| Standard deduction | $16,100 | $16,100 |
| QBI deduction | $11,650 | $3,776 |
| Taxable income | $46,598 | $15,102 |
| Federal income tax | $5,344 | $1,564 |
| Total federal tax | $16,648 | $12,868 |
Schedule C net profit
- No contribution
- $80,000
- $39,370 contribution
- $80,000
Self-employment tax
- No contribution
- $11,304
- $39,370 contribution
- $11,304
Deductible half of SE tax
- No contribution
- $5,652
- $39,370 contribution
- $5,652
Solo 401(k) contribution (Schedule 1)
- No contribution
- $0
- $39,370 contribution
- $39,370
Adjusted gross income
- No contribution
- $74,348
- $39,370 contribution
- $34,978
Standard deduction
- No contribution
- $16,100
- $39,370 contribution
- $16,100
QBI deduction
- No contribution
- $11,650
- $39,370 contribution
- $3,776
Taxable income
- No contribution
- $46,598
- $39,370 contribution
- $15,102
Federal income tax
- No contribution
- $5,344
- $39,370 contribution
- $1,564
Total federal tax
- No contribution
- $16,648
- $39,370 contribution
- $12,868
Computed with the site's 2026 tax code: Form 1040-ES rate schedule, $16,100 standard deduction, Schedule SE and the QBI deduction. Single filer, no other income, no state tax. The $39,370 is the Solo 401(k) maximum at this profit from the retirement contribution calculator. Rounded to the dollar.
The example assumes a single filer under 50, taking the 2026 standard deduction, with no other income and no state tax.
Self-employment tax is $11,304 in both columns. All of the $3,780 saved, $16,648 minus $12,868, is income tax.
The saving is smaller than you might expect from a $39,370 deduction. The QBI deduction is based on your business income after retirement contributions, so it falls from $11,650 to $3,776 when you contribute. Our QBI guide explains why. Both effects are already in the numbers above.
The same test at other profit levels, with the maximum Solo 401(k) contribution for each:
| Net profit | SE tax, both cases | Maximum contribution | Income tax, none | Income tax, maximum | Income tax saved |
|---|---|---|---|---|---|
| $30,000 | $4,238 | $27,881 | $943 | $0 | $943 |
| $60,000 | $8,478 | $35,652 | $3,559 | $321 | $3,238 |
| $80,000 | $11,304 | $39,370 | $5,344 | $1,564 | $3,780 |
| $100,000 | $14,129 | $43,087 | $8,235 | $2,992 | $5,243 |
| $150,000 | $21,194 | $52,381 | $16,413 | $7,194 | $9,219 |
$30,000
- SE tax, both cases
- $4,238
- Maximum contribution
- $27,881
- Income tax, none
- $943
- Income tax, maximum
- $0
- Income tax saved
- $943
$60,000
- SE tax, both cases
- $8,478
- Maximum contribution
- $35,652
- Income tax, none
- $3,559
- Income tax, maximum
- $321
- Income tax saved
- $3,238
$80,000
- SE tax, both cases
- $11,304
- Maximum contribution
- $39,370
- Income tax, none
- $5,344
- Income tax, maximum
- $1,564
- Income tax saved
- $3,780
$100,000
- SE tax, both cases
- $14,129
- Maximum contribution
- $43,087
- Income tax, none
- $8,235
- Income tax, maximum
- $2,992
- Income tax saved
- $5,243
$150,000
- SE tax, both cases
- $21,194
- Maximum contribution
- $52,381
- Income tax, none
- $16,413
- Income tax, maximum
- $7,194
- Income tax saved
- $9,219
Same method and assumptions as the table above: 2026 standard deduction and rates, QBI deduction after the contribution, no other income, no state tax. The maximum contribution is the Solo 401(k) maximum from our retirement contribution calculator (a $24,500 deferral plus the employer part, limited by compensation at $30,000). The SE tax column is the same with and without the contribution.
What does lower self-employment tax
Anything that lowers your Schedule C profit does. Business expenses are the usual way: software, equipment, a home office, business mileage and fees all come off the profit that self-employment tax is figured on. The self-employment tax calculator shows the result for your own profit.
| Deduction | Lowers SE tax? | Lowers income tax? |
|---|---|---|
| Business expense on Schedule C (software, equipment, mileage, home office) | Yes | Yes |
| Solo 401(k) or SEP IRA contribution (Schedule 1, line 16) | No | Yes |
| Deductible half of SE tax (Schedule 1, line 15) | No | Yes |
| HSA deduction (Schedule 1, line 13) | No | Yes |
| Self-employed health insurance deduction (Schedule 1, line 17) | No | Yes |
| Standard deduction and QBI deduction | No | Yes |
Business expense on Schedule C (software, equipment, mileage, home office)
- Lowers SE tax?
- Yes
- Lowers income tax?
- Yes
Solo 401(k) or SEP IRA contribution (Schedule 1, line 16)
- Lowers SE tax?
- No
- Lowers income tax?
- Yes
Deductible half of SE tax (Schedule 1, line 15)
- Lowers SE tax?
- No
- Lowers income tax?
- Yes
HSA deduction (Schedule 1, line 13)
- Lowers SE tax?
- No
- Lowers income tax?
- Yes
Self-employed health insurance deduction (Schedule 1, line 17)
- Lowers SE tax?
- No
- Lowers income tax?
- Yes
Standard deduction and QBI deduction
- Lowers SE tax?
- No
- Lowers income tax?
- Yes
Net profit from Schedule C is the starting point of Schedule SE (Instructions for Schedule SE); Schedule 1 adjustments come after it. Line numbers are from the 2025 Schedule 1 and may change on the 2026 form.
The same logic applies to a SEP IRA, since its deduction also sits on Schedule 1. If you’re comparing the two plans, the Solo 401(k) vs. SEP IRA guide is about how much each lets you contribute, not about this tax.
If you have an S corporation
An S corporation owner who takes a salary pays payroll tax on that salary instead of self-employment tax on the whole profit. The retirement plan then interacts with payroll tax in two different ways, per the IRS rules on contributions and FICA:
- Employee deferrals are still Social Security and Medicare wages. Deferring part of your salary doesn’t lower the payroll tax on it.
- Employer contributions (matching and profit-sharing) aren’t wages, so no Social Security or Medicare tax applies to them.
Employer contributions are based on your W-2 salary, not on the company’s profit, so a modest salary means a smaller employer contribution. The IRS also expects the salary to be reasonable for the work you do (IRS).
| W-2 salary | Employee deferral | Employer part (25%) | Total | FICA not paid on the employer part |
|---|---|---|---|---|
| $40,000 | $24,500 | $10,000 | $34,500 | $1,530 |
| $60,000 | $24,500 | $15,000 | $39,500 | $2,295 |
| $80,000 | $24,500 | $20,000 | $44,500 | $3,060 |
| $100,000 | $24,500 | $25,000 | $49,500 | $3,825 |
$40,000
- Employee deferral
- $24,500
- Employer part (25%)
- $10,000
- Total
- $34,500
- FICA not paid on the employer part
- $1,530
$60,000
- Employee deferral
- $24,500
- Employer part (25%)
- $15,000
- Total
- $39,500
- FICA not paid on the employer part
- $2,295
$80,000
- Employee deferral
- $24,500
- Employer part (25%)
- $20,000
- Total
- $44,500
- FICA not paid on the employer part
- $3,060
$100,000
- Employee deferral
- $24,500
- Employer part (25%)
- $25,000
- Total
- $49,500
- FICA not paid on the employer part
- $3,825
Same logic as our retirement contribution calculator's S corp mode: the employer part is 25% of W-2 salary, and the total is limited to $72,000 and to your compensation. The last column is 15.3% of the employer part (our arithmetic): the Social Security and Medicare tax, both halves, that would apply if the same dollars were paid as extra salary. The $24,500 deferral is still subject to FICA.
This isn’t a reason to elect S corporation status. That decision has its own costs and rules, and the S Corp guide and S Corp calculator cover it.
Where the savings are
A Solo 401(k) is an income tax tool. For a sole proprietor, the self-employment tax is the same with or without it, so judge the contribution on income tax and on what you want in retirement.
Following the numbers through the forms
On the 2025 Schedule SE, line 4a multiplies your net earnings by 92.35%. Line 10 applies 12.4% to the smaller of your earnings or what remains of the Social Security wage base, which the form lists as $176,100 for 2025, and line 11 applies 2.9% to all of the earnings. Line 12 adds them to get self-employment tax, and line 13 takes 50% of it for the deduction that goes to Schedule 1, line 15. The IRS says that deduction only affects income tax and does not change net earnings from self-employment or the self-employment tax.
Everything else that reduces income comes later and lands on Schedule 1: the HSA deduction on line 13, the deductible part of self-employment tax on line 15, self-employed SEP, SIMPLE and qualified plans on line 16, and self-employed health insurance on line 17. Schedule SE has no lines for any of them. That is the whole reason the answer is no. The IRS also notes that the Social Security Administration uses the information from Schedule SE to figure your benefits, so what you report there is what your record shows.
How your own contribution is calculated
Because you are both the employee and the employer, the IRS says you cannot apply a flat plan percentage to Schedule C profit. Your plan compensation is your net earnings from self-employment reduced by the deductible part of self-employment tax and by your own plan contribution. The two depend on each other, so the IRS describes it as a circular calculation and points to a reduced contribution rate in Publication 560.
The IRS gives a worked example. Joe has $100,000 of net profit and pays $14,130 of self-employment tax. Half is $7,065, which leaves $92,935. At a 10% plan rate the reduced rate is 10% divided by 110%, or 9.0909%, and his allowed contribution is $8,449. The check is to subtract the contribution and half the tax from profit and take 10% of what is left: $100,000 minus $7,065 minus $8,449 is $84,486, and 10% of that is $8,449. The IRS example uses 2019 figures and a 10% rate, so it illustrates the method and your 2026 limit will differ. For a one-participant 401(k), the owner contributes in two roles, deferring up to the annual limit ($24,500 in 2026) and adding an employer part of up to 25% of compensation, as the IRS defines it.
Where people go wrong
The mistake that does change self-employment tax is putting your own contribution in the wrong place. The IRS says plan contributions for a self-employed individual are deducted on Schedule 1 and kept off Schedule C. If you deducted it on Schedule C, or deducted more than the allowed amount, you should amend your Form 1040 and Schedule C. A Schedule C deduction would have lowered the profit that self-employment tax is figured on, and the IRS treats that as an error. Schedule C, line 19 is for contributions you make for your employees, and the instructions send contributions made on your own behalf to Schedule 1, line 16. The estimated payments guide matters here: the IRS says you can use estimated payments to pay self-employment tax, and since a contribution does not reduce that piece, your quarterly payments should not shrink on account of it. The set-aside guide shows how to separate the two pieces when you plan.
Another trap is timing. You can only know your profit, and with it the maximum contribution, once the year’s income and expenses are settled, so the amount you can defend is the one computed from the final Schedule C and the circular rate.
What a contribution saves per dollar
Since self-employment tax stays put, the saving is an income tax saving, and it depends on your bracket. Using the maximum contributions from the table above:
| Net profit | Maximum contribution | Income tax saved | Saved per dollar contributed |
|---|---|---|---|
| $30,000 | $27,881 | $943 | 3.4% |
| $60,000 | $35,652 | $3,238 | 9.1% |
| $80,000 | $39,370 | $3,780 | 9.6% |
| $100,000 | $43,087 | $5,243 | 12.2% |
| $150,000 | $52,381 | $9,219 | 17.6% |
$30,000
- Maximum contribution
- $27,881
- Income tax saved
- $943
- Saved per dollar contributed
- 3.4%
$60,000
- Maximum contribution
- $35,652
- Income tax saved
- $3,238
- Saved per dollar contributed
- 9.1%
$80,000
- Maximum contribution
- $39,370
- Income tax saved
- $3,780
- Saved per dollar contributed
- 9.6%
$100,000
- Maximum contribution
- $43,087
- Income tax saved
- $5,243
- Saved per dollar contributed
- 12.2%
$150,000
- Maximum contribution
- $52,381
- Income tax saved
- $9,219
- Saved per dollar contributed
- 17.6%
Our arithmetic: income tax saved divided by the maximum contribution, from the table above (same assumptions, federal only, QBI deduction after the contribution). The last column is not a return on the investment. It is the share of each contributed dollar that comes back as lower income tax this year.
At $30,000 of profit the saving is small because most of the income is already covered by the standard deduction. The percentage rises with profit, so the same contribution is worth more the higher your bracket. None of this changes self-employment tax, and the contribution is taxed when you take it out, unless the deferral is a designated Roth deferral, which is not deductible.
If you hire or become an employer
The IRS FAQ on FICA separates three kinds of money: employee pre-tax deferrals, which are subject to Social Security and Medicare tax but not income tax withholding; designated Roth deferrals, which are subject to both; and employer matching and nonelective contributions, which are subject to neither. The same table applies to wages you pay others. The IRS also says that if you hire employees who meet the plan’s eligibility requirements you must include them, and the no-testing advantage of a one-participant plan disappears. Compare the plan types in our Solo 401(k) vs. SEP IRA guide and ask a plan provider before you add staff.
What to do with this
- If you’re deciding between plans or how much to contribute, run your own numbers in the Solo 401(k) vs. SEP IRA calculator, which shows the maximum and the income tax a contribution saves.
- If you want to lower self-employment tax itself, look at Schedule C: what you can legitimately deduct as a business expense.
- If you have an S corporation or are thinking about one, talk to a qualified tax professional. The right answer depends on your salary, state and the plan documents.
How we got these figures
The tax rates and the 92.35% base come from the IRS self-employment tax page and the Schedule SE instructions; the Schedule 1 adjustments from the 2025 Schedule 1; the Solo 401(k) rules (the 25% employer part and the earned income definition) from the IRS one-participant 401(k) page and Publication 560; the FICA treatment of deferrals and employer contributions from the IRS retirement plan FAQ (reviewed April 8, 2026); the $24,500 deferral limit from IR-2025-111 and the $72,000 limit from Notice 2025-67. We opened them all on October 15, 2026, plus the 2025 Schedule SE form and the IRS page on calculating your own plan contribution, and quote the passages in our research file. The IRS self-employment tax page still shows 2024 wage base figures, so we rely on the 2025 Schedule SE form for the line-by-line steps. The tables are our own arithmetic with the same functions our retirement calculator uses, rounded to the dollar. For how we pick and check sources, see How We Research.
