Financial calculators that run the numbers for you.
Model your 401k, taxes, take-home pay, and retirement date paycheck by paycheck. Built for people with multiple jobs, RSUs, and real-life tax complexity.
Get every dollar into Roth that the IRS will let you.
- +Solve optimal 401k % across W2 and 1099 jobs
- +Preserve full employer match (no front-loading)
- +See real tax liability vs. withholding
See when you can actually retire.
- +Historical (1871-2024), Monte Carlo, or fixed-rate
- +Model raises, expenses, side income streams
- +Sensitivity charts for spending and returns
Know your real take-home, in any state.
- +Compare up to 6 states side-by-side
- +Federal, FICA, and progressive/flat state tax
- +Pre-tax + post-tax deductions, bonuses, overtime
The Mega Backdoor Roth
Up to $47,500.00 per employerA Roth account is one of the most powerful retirement tools available: tax-free growth, tax-free withdrawals, and you can pull out contributions at any time without penalty. The catch is that direct Roth contributions are capped at $24,500.00 per year through your 401k. The mega backdoor Roth is a strategy that lets you get significantly more in - up to $47,500.00 more per employer per year.
Why Roth Money Is Different
Investment gains in a Roth account are never taxed. In a pre-tax account, every dollar of growth will be taxed as ordinary income when you withdraw it. Over 20 to 30 years of compounding, this difference is substantial.
In retirement, Roth withdrawals don't count as income. This means they don't push you into higher tax brackets, don't increase your Medicare premiums, and don't trigger taxes on Social Security benefits.
Roth contributions (not earnings) can be withdrawn at any time without taxes or penalties. This makes Roth money more flexible than pre-tax retirement savings, which are locked until 59½.
Deciding between Roth and pre-tax 401k for your contributions? Read Roth vs Pre-Tax 401k: Which Is Better for You for the focused comparison.
The Two 401k Limits
The IRS imposes two separate limits on 401k contributions. Most people only know about the first. The mega backdoor Roth exploits the gap between them.
$24,500.00
The total pre-tax and Roth contributions you can make across all employers in a calendar year. This is the limit most people think of as “the 401k limit.”
$72,000.00
The total of all contributions at one employer: your elective deferrals + employer match + after-tax contributions. Each employer has its own independent bucket.
How the Mega Backdoor Roth Works
The strategy has two parts: make after-tax contributions to your 401k (beyond the elective limit), then convert them to Roth. The “backdoor” name comes from the fact that you're getting money into Roth through a side door, bypassing the normal contribution limits.
First, contribute the full $24,500 in pre-tax or Roth deferrals. These are the standard contributions most people make.
Your plan must support after-tax contributions (distinct from Roth). These come from your paycheck after income tax, and fill the gap between your elective + match and the $72,000 cap.
Convert after-tax dollars to Roth via an in-plan Roth conversion. Do this as soon as possible after each contribution to minimize taxable earnings in the after-tax account.
The optimizer has a full reference at the bottom of the page covering the 415(c) mechanics, per-employer rules, and IRS citations.
Why This Is Hard to Plan
The math seems simple on paper, but in practice there are several things that make it tricky to get right:
If you set elective percentages too high, you hit the $24,500 limit before December. Once contributions stop, so does your employer match for those paychecks. Unless your employer offers a true-up provision, that match is lost.
The elective limit is shared across all employers. If you change jobs mid-year, you need to track how much you already contributed and adjust at the new employer to avoid exceeding the limit.
Each employer withholds federal income tax as if they are your only employer. With multiple jobs or large after-tax contributions reducing take-home pay, your withholding may not match your actual tax liability.
Contribution percentages interact with pay frequency, bonus timing, and RSU vests. A percentage that works for regular paychecks may push you over limits when a bonus hits.
Popular Guides
A direct, focused comparison of Roth and pre-tax 401k for 2026.
How to get up to $72,000 per year into Roth through your 401k.
How the three 401k contribution types differ and when to use each.
A priority-order framework for picking your contribution rate.
Why front-loading can cost you thousands, and how to pace correctly.
Contribute to a Roth IRA when your income is above the direct limit.
Stop guessing. Run the numbers.
Free, no signup, your data stays in your browser. Read the full mega backdoor Roth guide or jump straight into a calculator.