Solo 401(k) Contribution Calculator 2026: Methodology and Sources

2026 constants used

• Employee elective deferral limit: $24,500
• Standard age-50 catch-up: $8,000
• Ages 60 to 63 catch-up: $11,250
• Annual additions limit excluding catch-up: $72,000
• Compensation cap: $360,000

Calculation flow

1. Cap compensation at the IRS compensation limit.
2. Set the elective deferral limit for the taxpayer’s age.
3. Separate the entered employee contribution into non-catch-up and catch-up pieces.
4. Calculate the employer contribution using either W-2 compensation or a self-employed earned-income approximation.
5. Cap the combined non-catch-up amount at the annual additions limit.
6. Add any permitted catch-up amount on top.

Assumptions and limits

• Self-employed mode is a planning estimate, not a filing worksheet.
• The calculator assumes one-participant plan conditions rather than a broader employee plan.
• Plan document restrictions and payroll timing are outside scope.
• State tax treatment is not included.

Primary sources

• IRS 2026 retirement limit announcement
• IRS Publication 560
• IRS one-participant plan guidance

Related pages: calculator and guide.

Update policy

We update this page when the IRS publishes new one-participant plan limits, catch-up amounts, annual additions caps, or compensation caps. We also revise the explanation if IRS guidance changes how we should describe self-employed contribution planning versus W-2 owner planning.

Estimate quality note

The W-2 owner branch is generally closer to filing reality because the compensation base is more straightforward. The self-employed branch is intentionally simplified for planning and should be treated as a decision-support estimate rather than a filing-ready computation.

Self-employed estimate detail

For self-employed planning, the calculator uses an earned-income approximation rather than a simple W-2 style percentage. The goal is to keep the estimate directionally accurate for decision-making without pretending to reproduce every line of a return worksheet. That matters because a flat 25% shortcut can overstate the employer contribution when the taxpayer is not paying themselves W-2 wages through an entity.

Because self-employed contribution math depends on the interaction between earnings and the contribution itself, this branch should be treated as a planning estimate. It is useful for comparing strategies, but the final filing result can still move once actual earned income is finalized.

What the tool does not model

This methodology does not attempt to model every plan-document deadline, payroll election issue, or controlled-group question that can affect a real one-participant plan. It also does not decide whether a taxpayer has already used part of the shared employee elective deferral limit in another employer's 401(k) plan. Those questions can materially affect the final number even when the general IRS limit table is correct.