Solo 401k Beitragsgrenze: Limits, Catch-Up und Fristen

For 2026, solo 401(k) contribution limits let a self-employed owner put away up to $72,000 in combined employee and employer contributions, rising to $80,000 at age 50 and $83,250 for participants aged 60 through 63.¹ The ceiling is high because the plan treats you as both the employee and the employer of your own business, giving you two separate contribution buckets to fill each year.

The Two Buckets: Employee Deferral and Employer Profit-Sharing

Every dollar you put into a solo 401(k) is either an employee elective deferral or an employer profit-sharing contribution. You wear both hats. The employee side is a flat dollar cap on what you can defer from your own compensation. The employer side is a percentage of that compensation your business contributes on top. Both count toward a single overall annual limit.²

What counts as “compensation” depends on your entity. S-corp and C-corp owners use W-2 wages the corporation pays them.³ Sole proprietors and partners filing Schedule C use net earnings from self-employment after subtracting one-half of self-employment tax and the employer contribution itself.⁴ That difference changes both the formula and the maximum you can put in.

Employee Deferral Limit for 2026

You can defer up to $24,500 of your compensation for 2026.⁵ You can split that between pre-tax and Roth in any proportion your plan document allows. The cap applies no matter how profitable your business is, though your compensation has to at least equal your deferral.

This limit is personal, not plan-specific. Deferrals to every 401(k), 403(b), and governmental 457(b) you’re in must together stay under $24,500.⁵

Employer Profit-Sharing Limit for 2026

The employer contribution is a percentage of compensation, and the percentage depends on your entity type. Only the first $360,000 of compensation counts toward the calculation either way.⁶

If Your Business Is an S-Corp or C-Corp

The employer contribution can be up to 25% of your W-2 wages.⁴ At the $360,000 compensation ceiling that percentage would produce $90,000, but the overall combined limit of $72,000 caps you before you get there.

If You File Schedule C

For unincorporated businesses the effective rate is 20% of net adjusted self-employment income.⁷ The math looks like this:

Start with net profit from Schedule C.
Subtract the deductible half of your self-employment tax.
Subtract the employer contribution itself.
Apply 25% to what remains, which simplifies algebraically to 20% of net earnings after the self-employment tax adjustment.

Employer contributions are discretionary. You can contribute anywhere from zero up to the maximum in any year.

The Combined Ceiling and a Realistic Example

Employee deferrals and employer contributions together cannot exceed $72,000 for 2026.¹ Catch-up contributions sit on top of that ceiling rather than counting against it.²

Most participants hit the employer contribution math before reaching $72,000. Take a sole proprietor with $150,000 in Schedule C net profit. After the self-employment tax deduction, net adjusted self-employment income lands near $138,800. Twenty percent of that is roughly $27,750 on the employer side. Add the $24,500 deferral and the total comes to about $52,250. Reaching the full $72,000 generally takes net self-employment income above roughly $237,000.

Catch-Up Contributions by Age

Older participants get an extra layer on top of the $24,500 deferral. Three brackets apply for 2026.

Age 50 to 59, and 64 and Older

If you turn 50 by December 31, you can add $8,000 in catch-up deferrals, bringing the employee side to $32,500 and the combined maximum to $80,000.⁸ The same $8,000 catch-up applies from age 64 onward.

Age 60 Through 63: The Super Catch-Up

Under SECURE 2.0, participants who are 60, 61, 62, or 63 during the tax year get a larger catch-up. For 2026 that enhanced amount is $11,250, and it replaces rather than stacks on the standard $8,000.¹ The employee side maxes at $35,750 and the combined ceiling reaches $83,250.

2026 Maximums at a Glance

Under 50: $24,500 deferral, up to $72,000 total.
Age 50 to 59, or 64 and older: $32,500 deferral, up to $80,000 total.
Age 60 to 63: $35,750 deferral, up to $83,250 total.

Roth Catch-Up Rule Starting After 2026

For taxable years beginning after December 31, 2026, catch-up contributions for participants who earned more than $145,000 in FICA wages the prior year must be designated as Roth.⁹ For calendar-year plans that means 2027 is the first affected year. In 2026 you can still make pre-tax catch-ups regardless of income, but your plan document needs to accommodate Roth catch-ups before 2027.

Adding a Spouse Who Works in the Business

A solo 401(k) is limited to owner-only businesses, but a spouse who earns compensation from the business is an eligible participant rather than a disqualifying employee. Your spouse can make their own full set of employee deferrals and receive their own employer profit-sharing contributions. A working couple can effectively double the household’s contributions, potentially sheltering well over $140,000 a year depending on ages and income. The spouse has to receive legitimate W-2 wages or partnership self-employment income from the business.

Contribution Deadlines

One deadline is firm: your plan document must be formally adopted by December 31 of the year you want to start contributing. You cannot retroactively establish a solo 401(k) after the year closes. For the first year, you also need to make a written salary deferral election before the business’s year end.

Funding the account is more forgiving. Both the employee deferral and the employer contribution can be deposited as late as the business’s tax filing deadline, including extensions.⁴ A sole proprietor filing Form 1040 typically has until April 15, or October 15 with an extension.¹⁰ An S-corp filing Form 1120-S has a March 15 deadline, extendable to September 15.

That flexibility lets you finalize net income, calculate the optimal split, and deposit everything in one transaction well into the following year. The contribution is reported on the tax return for the year it applies to, not the year the money arrives.

If You Also Have a 401(k) at a W-2 Job

The two limits interact differently. Your employee deferral limit is shared across every plan you participate in; total deferrals cannot exceed $24,500, or $32,500 or $35,750 with the applicable catch-up.⁵ If your W-2 employer’s plan takes $18,000 of your deferrals, your solo 401(k) deferral is capped at $6,500.

The employer profit-sharing side is calculated separately for each unrelated business. Your W-2 employer’s match or profit-sharing has no effect on what your solo 401(k) business can contribute on the employer side. Each business applies the $72,000 overall limit independently.

Going over the aggregated deferral limit creates an excess deferral. You need to withdraw the excess plus earnings by your tax filing deadline for the year of the over-contribution. If you miss that, the IRS taxes the excess in the year you contributed it and taxes it again when you eventually distribute it.¹¹ Tracking deferrals across plans is your responsibility, not your employers’.

1
Internal Revenue Service. IRS Notice 2025-67
2
Internal Revenue Service. Fixing Common Plan Mistakes – Failure to Limit Contributions for a Participant
3
Internal Revenue Service. Retirement Plan FAQs Regarding Contributions – S Corporation
4
Internal Revenue Service. One-Participant 401(k) Plans
5
Internal Revenue Service. Retirement Topics – Contributions
6
Internal Revenue Service. Retirement Topics – 401(k) and Profit-Sharing Plan Contribution Limits
7
Internal Revenue Service. Publication 560 – Retirement Plans for Small Business
8
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026
9
Internal Revenue Service. Treasury, IRS Issue Final Regulations on New Roth Catch-Up Rule, Other SECURE 2.0 Act Provisions
10
Internal Revenue Service. FAQ – Due Date for Business Income Tax Returns
11
Internal Revenue Service. Consequences to a Participant Who Makes Excess Annual Salary Deferrals