Retirement
Solo 401(k) Contribution Limits Explained by Example
The two-layer contribution structure is what makes a Solo 401(k) so powerful — and also what makes it confusing the first time you calculate it. Here's a worked example.
As covered in our SEP IRA vs Solo 401(k) comparison, the Solo 401(k)'s advantage comes from contributing in two separate capacities. Here's how that actually adds up in practice.
The two contribution layers
- Employee deferral — a fixed dollar amount set annually by the IRS, the same limit that applies to any 401(k) participant, employee or self-employed.
- Employer profit-sharing contribution — up to 25% of your compensation (calculated slightly differently for the self-employed than for a W-2 employee), contributed in your capacity as the "employer."
These two layers combine, up to an overall annual dollar cap that's also set by the IRS each year and adjusted periodically for inflation.
Catch-up contributions for savers 50 and older
Savers aged 50 and up can add a catch-up contribution on top of the standard employee deferral limit. Under the SECURE 2.0 Act, there's an even higher "super catch-up" tier available specifically for savers aged 60 to 63, on top of the standard 50+ catch-up amount.
A simplified worked example
A 45-year-old freelancer with $120,000 in net self-employment earnings could potentially contribute: the full employee deferral amount, plus an employer contribution calculated as roughly 20% of net earnings after adjusting for the deductible half of self-employment tax (the effective employer-side percentage works out lower than a flat 25% once these adjustments are applied) — combined, this can mean contributing a substantial five-figure amount for the year, well beyond what a Roth IRA or SEP IRA alone would allow at the same income level.
The exact employer-contribution calculation involves a few adjustment steps specific to self-employment income — most Solo 401(k) providers and tax software calculate this automatically, and it's worth double-checking the exact figure with your plan provider rather than estimating by hand.
Why this level of detail matters
Because contribution limits are unusually generous compared to a typical employee 401(k), maximizing them can meaningfully reduce your current-year taxable income while building retirement savings at a pace few other structures allow for a solo business. Getting the calculation right — rather than under-contributing out of uncertainty — is worth the extra attention.
Frequently asked questions
Free Agent Finance Editorial Team
Contribution limits and catch-up rules are set annually and periodically revised — verify current figures with your plan provider or at IRS.gov. Have a correction? Let us know.
