Mega Backdoor Roth Calculator

Frequently Asked Questions

What is the 2026 mega backdoor Roth limit?

The total 415(c) limit is $70,000 in 2026. After subtracting your employee deferral ($23,500 base) and employer contributions, the remainder is your after-tax capacity. For many workers with a 50% match on 6%, the after-tax space can be $30,000-$40,000 per year.

Do all 401(k) plans allow the mega backdoor?

No. Your plan must explicitly permit after-tax (non-Roth) contributions AND offer an in-plan Roth conversion or in-service distribution to a Roth IRA. Check your Summary Plan Description or ask your HR department.

Is the mega backdoor Roth taxable?

After-tax contributions themselves are not deductible, but the conversion to Roth is generally tax-free if you convert promptly. Only earnings accumulated between contribution and conversion are taxable as ordinary income.

Can I use the mega backdoor Roth and the regular backdoor Roth?

Yes. They are separate strategies. You can contribute to a non-deductible IRA and convert to Roth (regular backdoor, $7,000-$8,000), and separately do after-tax 401(k) contributions plus in-plan conversion (mega backdoor, up to $40,000+).

Provided by AllCalculators.io
Free online calculators for everyday. No registration required.

Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

JavaScript is required to use the interactive calculator above. The questions and answers below remain readable without JavaScript.

How This Calculator Works

The mega backdoor Roth exploits the gap between the employee elective deferral limit ($23,500 for under-50 in 2026) and the IRS section 415(c) total annual additions limit ($70,000 in 2026). Your employer plan can accept after-tax (non-Roth) contributions to fill the gap between what you and your employer contribute and the $70,000 ceiling.

The calculator takes your expected employee deferral, employer contributions (match plus any profit-sharing), and the 415(c) limit, then outputs the after-tax capacity: after-tax space = $70,000 − employee deferral − employer contributions. If your plan allows either in-plan Roth conversions or in-service distributions to a Roth IRA, you can move that after-tax money to Roth each year with little or no additional tax.

Plan Requirements

Not all 401(k) plans allow the mega backdoor strategy. Two features are required:

After-tax (non-Roth) contributions: The plan document must permit employee contributions beyond the elective deferral limit that go into a separate after-tax bucket. These are distinct from Roth 401(k) contributions.

In-plan Roth conversion or in-service withdrawal: To complete the mega backdoor, you need a way to get the after-tax money into Roth while still employed. In-plan Roth conversion lets you convert the after-tax bucket directly to your Roth 401(k). An in-service distribution lets you roll the after-tax money to a Roth IRA.

Check your Summary Plan Description (SPD) or ask your HR or benefits administrator whether both features are available in your plan. Many large employer plans at major tech and financial companies do offer this, but many small-to-mid-size plans do not.

Tax Treatment of After-Tax Contributions

After-tax 401(k) contributions are made with dollars that have already been taxed - they are not deductible. When you convert them to Roth, only any earnings accumulated between the contribution date and the conversion are taxable (as ordinary income). If you convert promptly (same day or same week), the taxable amount is typically zero or near zero.

Once the money is in a Roth account (either the Roth 401(k) or a Roth IRA after a rollover), all future growth and qualified distributions are completely tax-free. The mega backdoor is essentially a way to turbocharge Roth savings far beyond the standard $23,500 or $7,000 IRA limits.

Mega Backdoor vs. Regular Backdoor Roth

The regular backdoor Roth (non-deductible traditional IRA contribution + conversion) adds only $7,000-$8,000 per year to your Roth accounts. The mega backdoor can add $30,000-$45,000+ per year, depending on how much you and your employer already contribute.

The regular backdoor is available to anyone with earned income regardless of their employer plan. The mega backdoor requires a permissive employer plan. High earners who have both options should generally use both: max the employee deferral (possibly as Roth 401(k)), capture the full employer match, convert the after-tax bucket via in-plan conversion, and then do the regular backdoor for the IRA as well.

Timing and Practical Tips

Convert frequently to minimize tax: Some plans let you do in-plan Roth conversions on a set schedule (monthly, quarterly). Converting after-tax money quickly prevents earnings accumulation that would be taxable.

Track Form 1099-R carefully: In-plan conversions generate a 1099-R. Ensure any taxable amount (earnings) is accurately reported; the basis from after-tax contributions must be tracked to avoid double-taxation.

Coordinate with income: If you are in the super catch-up window (ages 60-63), the 415(c) limit slightly changes the arithmetic but the strategy remains valid.

Check plan rules annually: Employers can change plan features; confirm after-tax contributions are still allowed each year.

Tax laws change frequently. Verify current limits at IRS.gov and consult a qualified financial advisor before making retirement decisions.

Mega Backdoor Roth Calculator

Frequently Asked Questions

Related Retirement Calculators