Solo 401k Contribution Calculator

What This Calculator Does and Why It Matters

If you are self-employed — whether as a sole proprietor, freelancer, or single-member LLC owner — a Solo 401(k) is one of the most powerful retirement accounts available to you. This free solo 401k contribution calculator shows you exactly how much you can contribute for the year based on your actual net self-employment income.

Unlike a regular employer’s 401(k), a Solo 401(k) lets you contribute as both the employee and the employer. That dual contribution structure means you can shelter a significant portion of your income from taxes each year. This calculator applies the correct IRS formulas and 2025–2026 limits, including catch-up contributions for those age 50 and older.

Knowing your contribution limit ahead of tax season helps you plan deposits, reduce taxable income, and avoid over-contributing — which triggers IRS penalties. Use this tool any time you want a fast, accurate breakdown of what you can put away.

How to Use This Calculator

Step-by-Step Instructions

1. Enter your net self-employment income — this is your business profit after all deductible expenses, not gross revenue.
2. Enter your age. If you are 50 or older, you qualify for an additional catch-up contribution on top of the standard employee deferral limit.
3. Select the tax year you are calculating for — 2025 or 2026.
4. Choose your contribution type: employee only, employer only, or both (most common).
5. Click Calculate Contribution to see your full breakdown, including the IRS Section 415(c) annual limit check.
6. Click Reset to enter a new scenario.

The Formula Explained

The Solo 401(k) contribution formula involves two separate calculations — one for the employee side and one for the employer (profit sharing) side. Most people contribute to both to maximize their total annual shelter.

Breaking Down the Formula

First, the IRS requires you to deduct half of your self-employment tax from your net income before calculating contributions. This gives you your “net earnings from self-employment.” On the employee side, you can defer up to 100% of your net earnings or the annual deferral limit ($23,500 in 2025–2026), whichever is lower. On the employer (profit sharing) side, you can contribute up to 20% of your net earnings — note that for sole proprietors, this is 20%, not 25%, which is the rate for S-corps and C-corps.

The IRS Section 415(c) annual limit — $70,000 for 2025–2026 — is a hard ceiling on the combined total of both contributions. For those 50 and older, the limit rises to $77,500 after catch-up. You can find the official limits published on the IRS Solo 401(k) plan page.

Example Calculation with Real Numbers

Suppose you are 52 years old with $120,000 in net self-employment income. Half of your SE tax deduction is approximately $8,479, leaving net earnings of about $111,521. Your maximum employee deferral is $23,500, plus a $7,500 catch-up for a total of $31,000 on the employee side. Your employer contribution is 20% of $111,521, which is $22,304. Combined: $31,000 + $22,304 = $53,304 — well under the $77,500 limit. That is $53,304 you can potentially shield from federal income tax this year.

When Would You Use This

This calculator is most useful at the start of the year when planning contributions, or at year-end before the contribution deadline. You can also run it mid-year if your income has changed significantly and you want to know whether you are on track to maximize your limit.

Real Life Use Cases

Freelancers and independent consultants often discover they can shelter far more income with a Solo 401(k) than with a SEP-IRA, especially once they are over 50. If you want to compare both options side by side, the SEP-IRA contribution calculator for self-employed is a great companion tool. You should also be aware of the self-employment tax calculator for 2026 to make sure your SE tax deduction inputs are accurate before running contribution estimates.

Specific example scenario

A 44-year-old graphic designer earns $85,000 in net profit. After the SE tax deduction, net earnings are about $78,974. She maxes her employee deferral at $23,500 and adds a 20% employer contribution of $15,795. Total contribution: $39,295 — reducing her taxable income by nearly $40,000 for the year. That kind of tax impact is why high-earning freelancers prioritize Solo 401(k) setup.

Tips for Getting Accurate Results

Use Net Profit, Not Gross Revenue

The most common mistake is entering gross revenue instead of net profit. Your Solo 401(k) contribution is based on what is left after deductible business expenses. If you enter the wrong number, your calculated limit will be off — possibly by tens of thousands of dollars.

Confirm Your Entity Type With a CPA

The 20% employer contribution rate applies to sole proprietors and single-member LLCs taxed as sole props. If you own an S-corp and pay yourself a W-2 salary, the formula is different — and potentially allows for a 25% contribution rate. According to Investopedia’s Solo 401(k) guide, entity structure significantly affects how contributions are calculated. Always confirm with a CPA.

Do Not Miss the Contribution Deadline

The employee deferral portion must be elected by December 31st of the tax year. The employer profit sharing contribution can be made up to the tax filing deadline, including extensions (typically October 15th). Missing the election deadline means losing the deferral for that year. If you also use a solo 401(k) for long-term planning, consider running the 401(k) early withdrawal penalty calculator to understand the cost of accessing these funds early.

Frequently Asked Questions

Who qualifies for a Solo 401(k)?

Any self-employed person with no full-time employees other than a spouse qualifies for a Solo 401(k). This includes sole proprietors, freelancers, independent contractors, and single-member LLC owners. If you hire a full-time employee who is not your spouse, you must switch to a different retirement plan type.

What is the Solo 401(k) contribution limit for 2026?

For 2026, the total combined contribution limit is $70,000, or $77,500 if you are age 50 or older and make catch-up contributions. The employee deferral portion is capped at $23,500, with an additional $7,500 catch-up for those 50 and older.

Can I make both traditional and Roth contributions to a Solo 401(k)?

Yes, if your Solo 401(k) plan document allows it. The Roth option lets you make after-tax employee deferrals, which grow tax-free. The employer profit sharing contribution, however, must always go into the traditional (pre-tax) side. Not all Solo 401(k) providers offer the Roth option, so check your plan documents.

Is a Solo 401(k) better than a SEP-IRA for self-employed people?

In most cases, yes — especially once you have substantial income. A Solo 401(k) allows higher contributions at lower income levels because of the employee deferral component. A SEP-IRA only allows employer contributions (25% of W-2 compensation or 20% of net earnings for self-employed). The Solo 401(k) typically wins unless your income is very high and you want simpler administration.

What happens if I over-contribute to my Solo 401(k)?

Excess contributions must be withdrawn by April 15th of the following year, along with any earnings on the excess amount. If you miss that deadline, the excess is subject to both income tax and a 6% excise tax for every year it remains in the account. This is a serious and costly mistake to avoid.

Does my Solo 401(k) require annual tax filings?

Once your Solo 401(k) plan assets exceed $250,000, you are required to file Form 5500-EZ with the IRS each year. Below that threshold, no annual return is required. Keep records of all contributions and plan documents regardless of whether a filing is required.

Can my spouse also contribute to my Solo 401(k)?

Yes. If your spouse earns compensation from your business, they can also participate in the plan. This effectively doubles the contribution opportunity and is one of the biggest advantages of the Solo 401(k) structure for couples who work together.

When is the deadline to open a Solo 401(k)?

For most plan types, you must establish the Solo 401(k) plan by December 31st of the tax year in which you want to make contributions. Thanks to the SECURE Act, businesses that file for an extension may have until the extended deadline to establish a new plan — but this depends on the specific plan type and provider.

Conclusion

A Solo 401(k) is one of the most tax-efficient tools available to self-employed professionals. This calculator gives you a fast and accurate picture of how much you can contribute based on your actual 2025 or 2026 income, age, and contribution preferences.

Always verify your final contribution amount with a CPA or financial advisor before depositing funds. The formula has several nuances — especially around entity type and the SE tax deduction — where small errors can add up to big differences in your legal contribution limit.