Solo 401(k) Calculator: Self-Employed Contribution Limits

Enter your net self-employment profit (or your W-2 salary if your business is an S corporation), your age, and your marginal tax rate to see the largest solo 401(k) contribution the law allows for 2026, how much of it is deductible, and what it could grow to by retirement.

For the rules behind these numbers, read 401k Contribution Limits for Self-Employed.

Short answer: for 2026 a solo 401(k) lets you defer up to $24,500 as the "employee" and add an "employer" contribution of 20% of net profit after half of self-employment tax (25% of salary for an S-corporation owner). Those two together are capped at $72,000, and catch-up contributions of $8,000 at 50+ or $11,250 at ages 60–63 go on top, according to IRS Notice 2025-67. A sole proprietor with $150,000 of profit can put in about $52,381.

The calculator is for informational purposes only. It produces an estimate from the figures you type in, and it does not know about other plans you contribute to, so check the result against your own records before you make a deposit.

What are the 2026 solo 401(k) limits?

A solo 401(k) (also called a one-participant or individual 401(k)) is an ordinary 401(k) plan that covers only the business owner, or the owner and spouse (IRS: One-participant 401(k) plans). The same limits apply as in any 401(k):

Catch-up contributions are not counted against the $72,000. So the most one person can contribute for 2026 is $80,000 at ages 50–59 or 64 and older, and $83,250 for someone who turns 60, 61, 62 or 63 during 2026. The age test looks at the age you reach by December 31, so a 59-year-old who turns 60 in November qualifies for the larger catch-up for the whole year. Every 2026 inflation adjustment is collected in the 2026 IRS inflation adjustments guide.

How the calculator works out your maximum

The math follows the "Deduction Worksheet for Self-Employed" in IRS Publication 560. It takes four steps.

Step 1: plan compensation

• Sole proprietor, single-member LLC or partner: start from net profit (Schedule C line 31, or your partnership self-employment income). Self-employment tax is figured on 92.35% of it: 12.4% Social Security up to the $184,500 wage base and 2.9% Medicare on everything. Subtract the deductible half of that SE tax. What is left is your plan compensation.
• S-corporation owner: your compensation is the W-2 salary the corporation pays you. Distributions on your K-1 do not count, which is why S-corp owners who keep salaries low also have low solo 401(k) limits.

Step 2: the employer (profit-sharing) contribution

A sole proprietor's employer contribution is 20% of plan compensation. The plan's rate is 25%, but because your compensation is itself reduced by the contribution, the IRS rate table converts 25% into an effective 20%. An S-corporation contributes up to 25% of your W-2 salary. In both cases only the first $360,000 of compensation counts.

Step 3: the employee deferral

You can defer up to $24,500, but never more than the compensation left after the employer contribution. Your deferral does not reduce the base for the employer contribution, which is a common mistake in spreadsheets: the 20% is taken on the full plan compensation.

Step 4: the caps

Deferral plus employer contribution cannot exceed $72,000 or 100% of compensation, whichever is smaller. When the sum is over the cap, the calculator trims the employer contribution. The catch-up is then added on top, limited to whatever compensation is still left.

Worked examples with 2026 numbers

Sole proprietor, $150,000 net profit, age 45

1. Net earnings from self-employment: $150,000 × 92.35% = $138,525.
2. SE tax: $138,525 × 15.3% = $21,194.33. Half of it, $10,597.16, is deductible.
3. Plan compensation: $150,000 − $10,597.16 = $139,402.84.
4. Employer contribution: 20% × $139,402.84 = $27,880.57.
5. Employee deferral: $24,500.
6. Total: $52,380.57, well under the $72,000 cap.

At a 24% marginal rate, contributing all of it pre-tax cuts federal income tax by about $12,571.

Sole proprietor, $300,000 net profit, age 61

1. Net earnings: $300,000 × 92.35% = $277,050. Social Security tax stops at the wage base: $184,500 × 12.4% = $22,878. Medicare: $277,050 × 2.9% = $8,034.45. SE tax: $30,912.45; half is $15,456.23.
2. Plan compensation: $284,543.78. Employer contribution at 20%: $56,908.76.
3. Deferral $24,500 + employer $56,908.76 = $81,408.76, which is over $72,000, so the employer share is cut to $47,500.
4. Catch-up for age 61: $11,250.
5. Total: $83,250, the 2026 maximum for this age.

S-corporation owner, $100,000 W-2 salary, age 52

Employer contribution 25% × $100,000 = $25,000; deferral $24,500; catch-up $8,000. Total $57,500. To reach the $72,000 annual additions cap with a $24,500 deferral, the salary would have to be $190,000, because 25% of $190,000 is $47,500.

How much profit does it take to max out?

Below those amounts, the employer contribution is the limiting factor and the calculator shows "Income Limited Contributions."

How to read the tax savings

The calculator separates contributions into pre-tax money and Roth money:

• Maximum Traditional: everything is deductible.
• Maximum Roth: your employee deferral and catch-up are Roth (taxed now, tax-free later if you meet the five-year and age 59½ rules); the employer contribution stays pre-tax.
• Balanced: half of your employee money is Roth.
• Income-Based: employee money goes pre-tax when your marginal rate is 24% or higher and Roth when it is lower.

"Income tax saved this year" is the pre-tax amount times the marginal rate you entered, so use the federal plus state rate on your last dollar of income. The federal tax bracket calculator shows which bracket you are in.

The savings never include self-employment tax. Contributions for a sole proprietor are deducted on Schedule 1, line 16, after SE tax has already been figured on Schedule SE, so they do not change it. If you want to see SE tax and income tax on your profit together, use the 1099 tax calculator.

SECURE 2.0 also lets a plan accept Roth employer contributions. The calculator treats employer money as pre-tax because most providers' solo 401(k) documents default to that and because a Roth employer contribution is taxable to you in the year it is made.

Solo 401(k) compared with a SEP IRA and a SIMPLE IRA

A SEP IRA reaches the same $72,000 ceiling only at much higher profit because it has no employee deferral. At $150,000 of profit, the SEP maximum is $27,880.57, compared with $52,380.57 in a solo 401(k). The calculator shows both side by side. SIMPLE IRA figures are from Notice 2025-67; some small employers can use the higher $18,100 limit.

Deadlines and paperwork

• Opening the plan: a sole proprietor can establish a new solo 401(k) after year-end, up to the return due date not counting extensions, and still make employee deferrals for that first year under SECURE 2.0. Existing plan owners make their deferral election by December 31.
• Employer contributions: due by the business's tax return due date, including extensions (October 15, 2027 for a sole proprietor on extension for 2026).
• S-corporation deferrals: come out of payroll, so they must be withheld from paychecks during the year.
• Form 5500-EZ: required once plan assets exceed $250,000 at the end of a plan year, and for the final year of the plan. Late-filing penalties are steep, though the IRS runs a penalty relief program for late filers.

The Roth catch-up rule for higher earners

Starting in 2026, anyone whose FICA wages from the plan's sponsor exceeded $150,000 in 2025 must make catch-up contributions as Roth contributions. In a one-person plan this reaches only S-corporation owners, because sole proprietors and partners have self-employment income, not FICA wages. The calculator flags the rule when you choose S-Corporation and enter a salary above $150,000 with a catch-up. Using last year's salary is the correct test, so if your salary changed a lot, check against your 2025 Form W-2, box 3.

Common mistakes the calculator avoids

• Using gross profit: contributions are based on net profit after the deduction for half of SE tax, not on revenue or on net profit before it.
• Taking 25% for a sole proprietor: the effective rate is 20%. A 25% rate on $139,402.84 would allow $34,851, which is $6,970 too much and would have to be removed as an excess contribution.
• Subtracting the deferral before figuring the employer share: this understates the employer contribution.
• Double-dipping the deferral limit: if you also defer at a W-2 job, your combined deferrals cannot exceed $24,500 plus catch-up. The calculator assumes the solo 401(k) is your only 401(k); reduce the deferral yourself if you already use part of it elsewhere.
• Counting the catch-up toward $72,000: catch-ups sit on top of the annual additions limit.
• Assuming a solo 401(k) cuts SE tax: it does not for a sole proprietor.

Business structure and solo 401(k) eligibility

A solo 401(k) is available when the business has no common-law employees other than you and your spouse. Part-time employees can change that: under SECURE 2.0, employees who work at least 500 hours in each of two consecutive years generally must be allowed to make deferrals. Once you hire, the plan has to be amended into a regular 401(k) or replaced.

• Sole proprietor or single-member LLC taxed as a disregarded entity: contributions are based on Schedule C profit.
• Partnership: each partner's contributions are based on that partner's own self-employment income, and the partnership makes the employer contributions.
• S corporation: contributions are based only on W-2 salary. A larger salary raises the 25% employer contribution but also costs 15.3% in payroll tax up to the wage base. The S-corp payroll tax calculator shows that trade-off, and the QBI deduction calculator shows how salary affects the 20% pass-through deduction.

Projection assumptions

The retirement projection grows your current solo 401(k) balance and adds the same total contribution at the end of every year at the return you enter. It does not inflate the limits or your income, and it does not take taxes off traditional balances. To compare taking the deduction now with paying tax later, run a conversion scenario in the Roth conversion calculator. If your income is near the $153,000 single or $242,000 joint Roth IRA phase-out, the backdoor Roth calculator shows how a Roth IRA fits alongside the plan.

Starting with tax year 2027, elective deferrals to a solo 401(k) can also count toward the federal Saver's Match for lower-income savers; employer profit-sharing does not count. The Saver's Match guide explains who qualifies.