Solo 401(k) Calculator

Enter net self-employment income and select whether you operate as a sole proprietor. The calculator uses a simplified self-employment-tax adjustment for sole proprietors. Enter age to determine whether the catch-up rules may apply, current plan balance and expected return to project growth, and retirement age to set the projection length.

The catch-up toggle matters only if the participant is at least 50 in the model. The code also identifies a higher catch-up amount for ages 60 through 63. The Roth portion input does not change the contribution-limit calculations shown in the supplied computation. Roth versus pre-tax treatment affects taxes, so do not interpret the contribution total as a tax recommendation.

The calculator first estimates the self-employment tax deduction used in its sole-proprietor calculation:

Self-employment tax deduction
= net income × 0.9235 × 0.5 × 0.153

Using the default $150,000 income:

$150,000 × 0.9235 = $138,525
$138,525 × 0.5 × 0.153 = $10,597.1625
$150,000 − $10,597.1625 = $139,402.8375 adjusted income

The employee deferral is limited by the 2026 employee limit and adjusted income. The calculator’s default result is $24,500.

For a sole proprietor, the employer contribution is calculated using 20% of the model’s adjusted compensation:

Employer compensation
= ($150,000 × 0.9235) − $10,597.1625
= $127,927.8375

Employer contribution
= $127,927.8375 × 20%
= $25,585.5675

The total is:

$24,500 employee deferral + $25,585.5675 employer contribution
= $50,085.5675 total annual contribution

Rounded to cents, that is $50,085.57. The result is below the calculator’s $72,000 base total limit, and the default participant is age 40 with catch-up disabled. The result card rounds the total to a whole dollar, so it may display $50,086.

For 2026, the calculator uses a $24,500 employee elective-deferral limit (IR-2025-111) and a $72,000 base total contribution limit. The employee limit is shared across most 401(k), 403(b), and 457(b) plans; if you defer through another employer plan, your available employee deferral may be lower.

The calculator’s catch-up assumptions are:

• Age 50 or older: $8,000 standard catch-up amount when enabled.
• Age 60 through 63: $11,250 super catch-up amount when enabled.
• Total limit with standard catch-up: the model uses an $80,000 total ceiling.
• Total limit with super catch-up: the model uses an $83,250 total ceiling.

Catch-up eligibility is not switched on merely because the age field qualifies. The calculator also has a separate catch-up input; set it appropriately and confirm the plan permits the contribution. SECURE 2.0 rules and plan administration affect eligibility and implementation. The IRS provides current retirement plan guidance.

A Solo 401(k) generally stops being a one-participant plan if the business hires eligible employees. Employee eligibility rules can require coverage even if the business owner would prefer to keep the plan limited to themselves. Ask a plan provider or tax professional how hiring affects the plan.

The calculator projects the account year by year. It starts with the current balance, applies the assumed return, and adds the annual contribution. For the default case, the contribution total is $50,085.5675 and expected return is 7%.

Annual investment growth = beginning balance × 0.07
Ending balance = beginning balance + annual contribution + annual investment growth

The calculator loops from age 40 through age 65. The supplied result includes 26 age entries, with contributions and growth applied after the initial age entry. Its precomputed outputs are:

• Projected balance at 65: $3,710,607
• Total contributions in the projection: $1,252,139
• Total modeled investment growth: $2,358,468
• Final-year contribution: $50,086
• Final-year growth: $239,473

These amounts reflect the tool’s annual timing convention and rounded display. Returns are assumed to be steady rather than variable. A 7% average assumption does not mean the account earns 7% every year, and the projection does not account for taxes, plan fees, changing income, or contribution-limit changes in future years.

A Solo 401(k) can allow substantial contributions when both employee and employer contributions are available. A SEP IRA may be simpler to administer, while a SIMPLE IRA has different limits and employer-contribution requirements. Compare the total contribution opportunity, setup and filing requirements, investment options, and access to the plan assets.

If you also work as an employee elsewhere, coordinate deferrals across plans. The annual employee deferral limit generally applies across plans, even when the plans have different employers. Employer contributions are handled separately, subject to applicable plan limits and rules. A 401(k) max contribution calculator can help compare an employee-plan contribution, while the 401(k) paycheck impact calculator focuses on take-home pay.

A Roth contribution is made with after-tax dollars, while traditional contributions may receive different tax treatment depending on the plan and the participant’s situation. The calculator’s Roth portion field does not model income taxes or future qualified withdrawal tax treatment. See how 401(k) withdrawals are taxed in retirement before interpreting the projected balance as spendable income.

Can I contribute the full $24,500 employee deferral and also make an employer contribution?

Yes, if you are eligible and the plan and compensation support both portions. The employee deferral and employer contribution are separate components, but the combined amount must remain within the applicable total limit. Contributions across multiple employer plans can also affect the employee deferral limit.

How do I calculate a sole proprietor’s employer contribution?

1. Estimate net earnings after the model’s self-employment-tax adjustment.
2. Calculate the employer contribution using the applicable rate—20% in this calculator’s sole-proprietor method.
3. Check the amount against the remaining total plan limit.
4. Verify the result with tax and plan documents because the deductible contribution calculation can depend on business structure and compensation.

Does the projected $3,710,607 balance mean I will have that much at age 65?

No; it is a constant-return projection, not a guarantee. Market returns vary, and actual results depend on contributions, timing, fees, taxes, and account investments. Test multiple return assumptions and avoid treating a single forecast as a promised balance.

Should I choose a Solo 401(k) or SEP IRA?

A Solo 401(k) may be attractive if you want employee deferrals in addition to employer contributions or need a participant loan feature offered by your plan. A SEP IRA can be simpler but has different contribution mechanics. The better choice depends on income, staff, other workplace plans, tax preferences, and administrative burden.

Does the calculator determine my tax deduction?

No; it estimates contribution amounts using simplified inputs. Deductibility and reporting depend on entity type, earned income, plan terms, and tax rules. Confirm the final contribution with current IRS guidance and a qualified tax preparer.

Do I need to file Form 5500-EZ?

Possibly. One-participant plans generally have annual filing requirements once plan assets reach the applicable threshold, and other circumstances can trigger reporting. The IRS explains one-participant plan requirements in its guidance for one-participant 401(k) plans.

Confirm that your business and plan qualify, check the current IRS limits, and coordinate employee deferrals with any other workplace plan. Then compare traditional and Roth treatment, fees, and administrative requirements. For a view of future withdrawals rather than contributions, use the 401(k) withdrawal calculator or 401(k) withdrawal tax calculator.