Mega Backdoor Roth Calculator

Answer four quick questions and get the exact 401(k) elections to set so you max out by December 31. All calculations happen in your browser.

How do you get paid?

This determines how many paychecks you have left this year.

Pick any past pay date (any weekday works)

Future pay dates are projected every 14 days from this date.

Your salary, your age, and any bonus still coming.

Base yearly salary ($)

Will you be 50 or older this year?

Do you have a bonus coming this year?

How the match is calculated decides your best contribution strategy.

How they match

They match this %

…up to this % of pay

Which contributions get matched?

Most plans match only pre-tax/Roth deferrals, but a few match after-tax contributions as well - your plan summary will say.

If you max out early, what happens to the rest of the year's match?

How to check yours - 2 minutes, worth real money

About 1 in 3 companies never pay back match you miss by maxing out early.

Search your 401(k) site's plan summary (or the SPD PDF) for “match”:

“each pay period”→ I'd lose it “true-up” / “annual reconciliation”→ they make it up “% of your contributions, up to $X”→ the dollar-cap type

Or ask HR: “If I max out early, is there a match true-up?”

Source: PSCA 68th Annual Survey of 401(k) Plans - 34% of periodic-match plans never true up.

Copy these three numbers from the year-to-date (YTD) column.

YTD employee 401(k) contributions (pre-tax + Roth)

YTD employer match

YTD after-tax contributions

Your answer

My plan takes elections in

Pre-tax / Roth Employer match After-tax

See the full math

IRS limits in use

Employee deferral limit (402(g))

Total limit, all sources (415(c))

Catch-up (50+)

Catch-up (60–63)

Presets fill official IRS numbers; fields stay editable for future years. The IRS publishes new amounts each November.