Mega Backdoor Roth Calculator
Mega Backdoor Roth Calculator
How much extra Roth room does your 401(k) really allow?
After-tax room available
0
can go in after-tax, then convert to Roth
Value if left in taxable brokerage instead
0
same growth, taxed on gains each year
Value if mega-backdoor'd to Roth
0
grows and withdraws completely tax-free
The mechanism
Your plan must allow (1) after-tax contributions beyond the regular deferral limit and (2) either in-service withdrawals or in-plan Roth conversions — not all 401(k) plans support this, confirm with your plan documents first.
Convert quickly
Any gains between contributing and converting are taxable — converting as soon as possible after each after-tax contribution (some plans do this automatically) minimizes the taxable sliver.
Why this beats a taxable account
The 2026 overall IRS 401(k) limit across employee deferrals, employer match, AND after-tax contributions combined is roughly $72,000 (indexed for inflation each year — confirm the current figure with your plan). After-tax room = overall limit minus your regular deferral minus your employer's match. This assumes your plan allows after-tax contributions and in-plan Roth conversion or in-service rollover to a Roth IRA — a meaningful share of plans don't offer this, so confirm with HR/your plan administrator before counting on it. Taxable-brokerage comparison assumes long-term capital gains tax annually on growth as a simplification; real taxable accounts are usually more tax-efficient than modeled here if held with index funds and rarely sold.
Frequently asked questions
How much do I actually need to retire comfortably?
It depends on your expected retirement expenses, Social Security benefit, and life expectancy -- there's no single universal number, though rules of thumb like "25x annual expenses" are a common starting point. This calculator lets you build a more specific estimate from your own numbers.Read more: Social Security Estimator: Why Claiming Age Changes Everything
What's the difference between a 401(k) and an IRA?
A 401(k) is employer-sponsored, often with an employer match, and has a higher annual contribution limit. An IRA is opened independently at a brokerage, with a lower contribution limit but typically far more investment choice. Many people contribute to both -- a 401(k) up to the employer match, then an IRA.Read more: Roth vs Traditional Calculator: Pay Tax Now or Pay Tax Later?
When should I claim Social Security -- 62, 67, or 70?
Claiming at 62 gives a permanently reduced benefit; waiting until your full retirement age (typically 66-67) gives the full benefit; waiting until 70 gives the maximum benefit, growing roughly 8% per year you delay past full retirement age. The right age depends on your health, other income, and whether you need the money sooner.Read more: Retirement Number Calculator: How Much Is Actually Enough?
How does inflation affect my retirement savings?
Inflation erodes purchasing power both before and during retirement, so a nominal dollar figure that looks sufficient today can fall short decades from now. This calculator shows results in both nominal and inflation-adjusted terms so you're not planning around a number that quietly loses value.Read more: Social Security Estimator: Why Claiming Age Changes Everything
Estimates only, not financial advice. See our Disclaimer.
