Solo 401(k) Roth vs Pre-Tax Calculator 2026 β 3-Bucket Split & Mega Backdoor
Calculate 2026 Solo 401(k) contributions across Roth, pre-tax, and after-tax buckets. Model $70,000 total cap, employer 25% contributions, mega backdoor Roth conversion, and projected after-tax retirement wealth.
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After business expenses, before 401(k) deductions years
Age 50+ adds $7,500 catch-up %
100% = max ($24,500 or $32,000 with catch-up) %
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Total Contribution
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Employee Elective
$0
Employer Profit-Sharing
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Current Year Tax Saved
Solo 401(k) Contribution Breakdown
How to Use This Solo 401(k) Calculator
Enter your net self-employment income after expenses. The calculator computes the maximum employee elective deferral ($24,500 or $32,000 with catch-up) and employer profit-sharing contribution (25% of net SE income). Select whether to make employee contributions as Roth or pre-tax. Pre-tax contributions reduce your current-year taxable income; Roth contributions create tax-free retirement income.
The Formula
Max Elective = $24,500 ($32,000 if age 50+, with $7,500 catch-up)
Employer Profit-Sharing = min(Net SE Γ 25%, $70,000 β Employee)
Total Cap = $70,000 ($77,500 with catch-up)
SE Tax Deduction First: Net SE for 25% = Gross SE Γ 92.35% Γ (1 β 25%/2)
Pre-Tax Tax Saved = Pre-Tax Employee Contrib Γ Marginal Rate
Employer Profit-Sharing = min(Net SE Γ 25%, $70,000 β Employee)
Total Cap = $70,000 ($77,500 with catch-up)
SE Tax Deduction First: Net SE for 25% = Gross SE Γ 92.35% Γ (1 β 25%/2)
Pre-Tax Tax Saved = Pre-Tax Employee Contrib Γ Marginal Rate
Example
$150,000 net SE income, age 42, pre-tax election:
SE tax deduction: $150K Γ 92.35% Γ 14.13% / 2 = ~$9,785 deduction
Net SE for profit-sharing: ~$140,215 Γ 25% = $35,054
Employee elective (pre-tax): $24,500
Total: $24,500 + $35,054 = $59,554 (under $70K cap)
Tax saved at 24%: $59,554 Γ 24% = $14,293
SE tax deduction: $150K Γ 92.35% Γ 14.13% / 2 = ~$9,785 deduction
Net SE for profit-sharing: ~$140,215 Γ 25% = $35,054
Employee elective (pre-tax): $24,500
Total: $24,500 + $35,054 = $59,554 (under $70K cap)
Tax saved at 24%: $59,554 Γ 24% = $14,293
Extended
3-Bucket Split Calculator & Multi-Year Projection
Drag sliders for Roth/Pre-tax/After-tax splits, model mega backdoor conversion, and see after-tax retirement wealth in an SVG chart
Allocate your employee elective contribution across three buckets. The employer profit-sharing always goes pre-tax. Mega backdoor allows after-tax voluntary contributions up to the total $70K cap.
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Employee Elective Allocation (must total β€ 100%)
Multi-Year Projection Table (Annual Contributions)
| Year | Age | Roth Balance | Pre-Tax Balance | After-Tax Balance | Total After-Tax Value |
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After-Tax Retirement Wealth by Bucket
Frequently Asked Questions
What are the 2026 Solo 401(k) contribution limits?
For 2026, the Solo 401(k) limits are: Employee elective deferral: $24,500 ($32,000 if age 50+ with $7,500 catch-up). Employer profit-sharing contribution: up to 25% of net self-employment income (after deducting the employer half of SE tax). Total combined limit: $70,000 ($77,500 with catch-up). Net SE income is calculated as gross business income minus business expenses minus the self-employment tax deduction.
What is the "mega backdoor" Roth with a Solo 401(k)?
If your Solo 401(k) plan documents allow it, you can make after-tax (non-Roth) voluntary contributions beyond the employee Roth/pre-tax elective limit β up to the $70,000 total cap less your other contributions. You then convert these after-tax contributions to Roth within the plan (in-plan Roth conversion) or roll them out to a Roth IRA. This creates tax-free growth for amounts far exceeding the normal $7,000 Roth IRA limit. Not all plan documents support this β check with your custodian.
Should I contribute pre-tax or Roth to my Solo 401(k)?
The classic advice: if your tax rate today is higher than your expected rate in retirement, choose pre-tax. If your rate today is lower (or you expect higher future rates), choose Roth. For self-employed individuals, years with low income are ideal for Roth contributions β you pay a low rate now for permanent tax-free growth. Years with very high income favor pre-tax to reduce current SE income and taxable income.
Is the employer profit-sharing contribution always pre-tax?
Yes. The employer profit-sharing contribution (25% of net SE income) must be pre-tax β there is no Roth employer contribution allowed for Solo 401(k) purposes. Only the employee elective deferral ($24,500 / $32,000 with catch-up) can be designated as Roth. This means at least the employer contribution portion will reduce your current-year taxable income regardless of your Roth/pre-tax election on the employee side.
What is the after-tax voluntary contribution and how is it taxed at retirement?
An after-tax voluntary contribution is a non-deductible contribution to the 401(k) β you pay tax on it now (no upfront deduction) but the money grows tax-deferred. At retirement, only the growth is taxable; the principal is tax-free (similar to a non-deductible IRA). The advantage is it can be converted to Roth (mega backdoor), converting the growth to tax-free status. Without conversion, it results in complex basis tracking (Form 8606 equivalent for 401(k)s).