Mega Backdoor Roth Calculator

Calculate how much you can contribute to a Roth account using the mega backdoor strategy. This powerful tool shows your potential after-tax 401(k) contribution room after accounting for your own pre-tax deferrals and your employer's match. See how these extra Roth contributions can grow into a significant source of tax-free income in retirement.

This calculator is for high-income earners whose 401(k) plan allows for after-tax contributions and in-plan Roth conversions or in-service withdrawals. If you've already maxed out your standard 401(k) contributions and Roth IRA, this strategy could be your next step. For a simpler Roth strategy, see the backdoor Roth calculator.

Enter your salary, contribution details, and age to see your available mega backdoor Roth space, a projection of your future Roth balance, and an estimate of the tax-free annual income it could generate. The results include a potential score and charts illustrating your Roth growth and contribution sources.

Start by entering your financial details in the "Income & 401(k) Details" section. Your annual salary is your gross pay before taxes. The pre-tax 401(k) contribution is the percentage of your salary you defer into your traditional or Roth 401(k), up to the annual employee limit. Add your employer's matching formula, including the match rate (e.g., 50%) and the match limit (e.g., up to 6% of your salary).

Next, in "Personal Details," provide your current age and planned retirement age. These inputs determine the timeline for your investment growth. The expected annual return is your estimate for the average investment performance of your Roth funds. A common long-term stock market average is between 7% and 10%, but you may want to use a more conservative number.

For a more detailed projection, open the advanced settings. Here you can input your current Roth balance from all sources (like a Roth IRA or Roth 401(k)) to see its combined growth with your new mega backdoor contributions. You can also add an annual raise rate to model how your salary and contribution potential might increase over time.

Annual Salary

This is your total gross income for the year, before any taxes or deductions are taken out. Your salary is a key factor because it determines the dollar amount of your 401(k) contributions and your employer's match, which in turn affects your available mega backdoor Roth space.

Pre-Tax 401(k) Contribution

Enter the percentage of your salary you contribute to your 401(k) plan. This includes both traditional (pre-tax) and Roth 401(k) deferrals. For 2026, the employee contribution limit is $23,500. The calculator will cap your contribution at this limit. Maximizing this contribution is often the first step before considering a mega backdoor strategy. Use the 401(k) contribution calculator to optimize this amount.

Employer Match Rate & Match Limit

These two fields define your company's 401(k) matching policy. The match rate is the percentage your employer contributes based on your own contributions (e.g., 50% or 100%). The match limit is the maximum percentage of your salary your employer will match. For example, a company that matches "50% up to 6%" of your salary would have a 50% match rate and a 6% match limit. Employer contributions count toward the total annual 401(k) limit and reduce your mega backdoor space, but it's free money you should always aim to capture.

Current Age & Retirement Age

Your current age and planned retirement age set the time horizon for the projection. A longer time horizon gives your mega backdoor Roth contributions more years to compound tax-free, which can lead to a much larger projected balance. Use our retirement age calculator to see how different retirement dates impact your overall plan.

Expected Annual Return

This is the average annual rate of return you anticipate on your investments within your Roth account. This is a long-term estimate, and actual returns will vary year to year. It's often wise to run scenarios with different return rates (e.g., 5%, 7%, 9%) to see a range of possible outcomes.

Current Roth Balance

This advanced input allows you to include your existing Roth savings from accounts like a Roth IRA or Roth 401(k). The calculator will add your projected mega backdoor contributions to this starting balance and project the growth of the total amount, giving you a more complete picture of your tax-free retirement assets.

Annual Raise Rate

Use this advanced input to model future salary increases. A steady raise can increase your employer match and potentially your ability to save over time. The calculator uses this percentage to adjust your salary each year in the projection, providing a more dynamic forecast.

This calculator determines your mega backdoor Roth potential by working backward from the total IRS 401(k) contribution limit. For 2026, this limit (defined by IRS section 415(c)) is $70,000 for individuals under 50. For those age 50 and over, a catch-up contribution of $7,500 increases the total limit to $77,500. Under the SECURE 2.0 Act, those aged 60-63 can make a "super catch-up" of $11,250 (instead of $7,500), raising the total limit to $81,250.

The calculation follows three main steps:

1. Calculate Employee & Employer Contributions: It first determines your total employee 401(k) deferrals (up to the $23,500 limit for 2026) and the total amount your employer contributes as a match.
2. Calculate Remaining Space: It subtracts both your contributions and your employer's contributions from the total annual limit ($70,000 or $77,500). The amount left over is your "mega backdoor Roth space." This is the maximum you can contribute in after-tax dollars to your 401(k).
3. Project Growth: The calculator then assumes you contribute this amount each year. It projects the growth of your Roth balance from your current age to your retirement age, compounding annually based on your expected return. It also factors in your current Roth balance and annual raises if you provide them.

The final results show your annual potential and the long-term impact on your tax-free retirement savings, helping you understand the value of this advanced strategy.

The calculator uses the following formulas to determine your mega backdoor Roth potential and project its growth.

Contribution Calculations

These formulas determine how much of the annual 401(k) limit is used by standard contributions.

employee_deferral = min(23500, annual_salary * (pre_tax_contribution_percent / 100))

contribution_for_match = min(employee_deferral, annual_salary * (match_limit_percent / 100))

employer_match_amount = contribution_for_match * (employer_match_rate_percent / 100)

Mega Backdoor Roth Space

This formula calculates your available room for after-tax contributions.

total_limit = if current_age >= 50 then 77500 else 70000

total_used = employee_deferral + employer_match_amount

mega_backdoor_space = max(0, total_limit - total_used)

Roth Balance Projection

The calculator projects your balance year by year. The formula for a single year's growth is:

investment_growth = current_roth_balance * (expected_return_percent / 100)

ending_balance = current_roth_balance + mega_backdoor_contribution_for_year + investment_growth

A mega backdoor Roth is a retirement savings strategy that allows high-income earners to contribute significantly more to a Roth account than standard IRA or 401(k) limits permit. It involves a two-step process:

1. After-Tax 401(k) Contributions: You make non-deductible, after-tax contributions to your 401(k) plan, beyond the standard employee deferral limit ($23,500 in 2026).
2. Roth Conversion or Withdrawal: You then immediately move those after-tax funds into a Roth account. This can be done through an in-plan conversion to your Roth 401(k) or an in-service withdrawal to an external Roth IRA.

The key is that the conversion of the after-tax contributions is a tax-free event. Any investment earnings on the after-tax money before it's converted would be taxable upon conversion, which is why it's best to perform the conversion as quickly as possible. Once the money is in a Roth account, all future growth and qualified withdrawals in retirement are completely tax-free.

This strategy is only possible if your 401(k) plan documents specifically allow for both (1) after-tax contributions and (2) either in-plan Roth conversions or in-service withdrawals. You must check with your plan administrator to confirm these features are available.

It's easy to confuse the "mega backdoor Roth" with the "backdoor Roth IRA," but they are two distinct strategies.

A Backdoor Roth IRA is for individuals whose income is too high to contribute directly to a Roth IRA. They make a non-deductible contribution to a Traditional IRA and then immediately convert it to a Roth IRA. This strategy is limited by the annual IRA contribution limit ($7,000 in 2026).

A Mega Backdoor Roth operates through a 401(k) plan and allows for much larger contributions. It uses the space remaining under the overall 401(k) limit ($70,000 in 2026) after employee and employer contributions are made. This can often amount to tens of thousands of dollars per year.

Both strategies help high earners get money into Roth accounts for tax-free growth, but the mega backdoor Roth offers significantly higher contribution potential. For a deeper dive, read about the Roth vs. Traditional IRA.

Mega Backdoor Space: This is the most important result. It shows the maximum amount you can contribute to your 401(k) as after-tax dollars this year, which can then be converted to a Roth account.

Total Roth / Year: This is the same as your mega backdoor space. It represents the total annual fuel for your tax-free growth engine.

Projected Roth Balance: This chart and number show how your current Roth balance, combined with your annual mega backdoor contributions, could grow by your planned retirement age. It demonstrates the powerful effect of compounding on these large, tax-advantaged contributions.

Tax-Free Income: This figure estimates the annual income your projected Roth balance could provide in retirement, based on the 4% rule. Since this income comes from a Roth account, it is completely tax-free, which is a major advantage in retirement planning.

Contribution Sources Donut Chart: This visual breaks down how the total annual 401(k) limit is being used. You can see the portions allocated to your pre-tax deferral, your employer's match, and the available mega backdoor Roth space.

If you want to maximize your mega backdoor Roth potential, here are a few strategies:

• Confirm Your Plan Allows It: The first and most critical step is to contact your 401(k) plan administrator or HR department. Ask them specifically: "Does our plan permit after-tax contributions and in-plan Roth conversions?" If not, this strategy is not available to you.
• Adjust Pre-Tax Contributions: While you should always contribute enough to get the full employer match, some people choose to contribute only up to the match limit in their pre-tax 401(k). This leaves more room under the $70,000 total limit for a larger mega backdoor Roth contribution. This is a tradeoff between a pre-tax deduction now and tax-free growth later.
• Automate the Process: Ask your plan administrator if you can set up automatic after-tax contributions and automatic in-plan conversions. This "set it and forget it" approach ensures you are consistently using the strategy and minimizes the risk of earnings accruing in the after-tax account before conversion.

1. Assuming Your Plan is Eligible: The most common mistake is attempting this strategy without confirming that the 401(k) plan allows both after-tax contributions and a conversion mechanism.
2. Forgetting to Convert: Making after-tax contributions without converting them to Roth defeats the purpose. The earnings on after-tax money are tax-deferred, not tax-free, and will be taxed as ordinary income upon withdrawal if not converted.
3. Confusing After-Tax with Roth 401(k): A "Roth 401(k)" contribution is part of your standard $23,500 employee limit. An "after-tax 401(k)" contribution is a separate type of contribution made on top of that limit.
4. Miscalculating the Limit: Forgetting to subtract both your own deferrals and your employer's match from the total limit can lead to over-contribution. Use the calculator to ensure your math is correct.