Solo 401(k) Contribution Calculator

A solo 401(k) takes two contributions from the same person, an employee deferral capped in dollars and an employer share capped as a percentage of compensation. Enter your Schedule C net profit or your W-2 wage, your age and the year's limits, and this returns the maximum for each half with every step shown. For a sole proprietor it deducts half the self-employment tax first and then applies the employer rate to compensation measured after the contribution itself, which turns the headline 25 percent into 20. Every IRS limit is an input because all of them are indexed each year.

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For net profit reported on Schedule C, or a partner's self-employment earnings. Half the self-employment tax comes off first, and the employer percentage is applied to what is left after the contribution itself, which is the step that turns 25% into 20%.

Schedule C line 31, or your share of partnership self-employment earnings. Before any retirement contribution and before the self-employment tax deduction.
Catch-up goes by the age you reach during the year, not your age today.
Wages from a job elsewhere. They fill the Social Security wage base first, which lowers the Social Security part of your self-employment tax.
The deferral limit belongs to you, not to the plan. Money you deferred at a day job uses it up before the solo plan sees any of it. The employer share is per employer and is not touched by this.
25% is the statutory ceiling. A lower figure is legitimate: the employer share is discretionary and you may put in less.
The ceiling on earnings subject to the 12.4% Social Security part. Indexed every year. Medicare at 2.9% has no ceiling.
The flat elective deferral limit for the year. Indexed by the IRS, so check the figure for the year you are contributing for.
Available from the year you reach 50. Also indexed.
SECURE 2.0 allows a higher catch-up in the years you are 60, 61, 62 or 63, and it drops back at 64. The plan document has to have adopted it.
The ceiling on the deferral and the employer share together, before catch-up. Indexed, and never more than your compensation.
The most compensation a plan may count when applying the employer percentage. Indexed.
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When the business pays you a wage, compensation is the W-2 figure and the employer percentage is applied to it directly. There is no self-employment tax step and no circular rate, because payroll tax and the contribution are already outside the wage.

Box 1 plus any elective deferrals, which is the plan compensation figure. A distribution or K-1 profit that is not a wage does not count and cannot support a contribution.
Catch-up goes by the age you reach during the year, not your age today.
The deferral limit belongs to you, not to the plan. Money you deferred at a day job uses it up before the solo plan sees any of it. The employer share is per employer and is not touched by this.
25% is the statutory ceiling. A lower figure is legitimate: the employer share is discretionary and you may put in less.
The flat elective deferral limit for the year. Indexed by the IRS, so check the figure for the year you are contributing for.
Available from the year you reach 50. Also indexed.
SECURE 2.0 allows a higher catch-up in the years you are 60, 61, 62 or 63, and it drops back at 64. The plan document has to have adopted it.
The ceiling on the deferral and the employer share together, before catch-up. Indexed, and never more than your compensation.
The most compensation a plan may count when applying the employer percentage. Indexed.
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