Mega Backdoor Roth Calculator 2026: Your After-Tax Contribution Room Under the $72,000 Overall 401(k) Limit

How much can I put in a mega backdoor Roth in 2026?

Up to the overall 401(k) limit of $72,000 minus your own deferral and everything your employer puts in (IRC §415(c); IRS Notice 2025-67). With a full $24,500 deferral and $10,000 from your employer, that leaves $37,500 of after-tax room; with no employer money, $47,500. Catch-ups sit outside the overall limit ($11,250 at ages 60 to 63), so at those ages the most that can go in is $83,250. Only plans that allow after-tax deposits and an in-plan Roth conversion or an in-service rollover can do it, so check yours first. If you convert straight away there are almost no earnings to tax; $500 of earnings at a 24% rate would cost $120.

Mega backdoor Roth room for 2026.
Key number2026
Overall limit (employee + employer + after-tax), catch-ups excluded (Notice 2025-67)$72,000
Employee deferral limit (Notice 2025-67)$24,500
After-tax room: full deferral + $10,000 employer$37,500
After-tax room: full deferral, no employer money$47,500
Most that can go in at ages 60 to 63 (Notice 2025-67)$83,250

Figures are the published 2026 limits quoted from the linked official sources; the calculators below are arithmetic on those limits and on the assumptions you type. Not tax advice: check a move with your plan administrator, custodian or tax preparer before acting.

Your 2026 after-tax room

The overall limit is also capped at 100% of your pay. Catch-ups are outside it. The earnings line assumes the earnings are converted to Roth with the rest and taxed at the rate you give; a plan that cannot separate them may tax a share of the whole conversion.

The arithmetic

The overall limit counts three things together: your deferrals (IRC §402(g), up to $24,500), the employer’s match and profit sharing, and after-tax deposits. Whatever room is left is the most after-tax money you can add: $72,000 − $24,500 − $10,000 = $37,500 in the example. A catch-up from age 50 is separate and does not use up any of it.

What makes it “backdoor”

After-tax deposits are not deductible, and their earnings are taxable when withdrawn. The point of the strategy is to move the after-tax money to a Roth account so the earnings from then on are tax-free: inside the plan, if it has an in-plan Roth conversion, or by an in-service distribution to a Roth IRA. When one payment is split between a Roth IRA and a traditional IRA or plan, the IRS lets you send the pre-tax amounts to one destination and the after-tax amounts to another, so the after-tax part can go to the Roth (IRS Notice 2014-54). Do the conversion promptly: the longer the after-tax money sits, the more earnings it carries, and those earnings are taxable when converted.

What your plan has to allow

The IRS limits are the ceiling; the plan document sets what you can actually do. Look in the summary plan description for three things: whether the plan accepts after-tax (non-Roth) deposits, whether it offers in-plan Roth conversions or in-service withdrawals, and whether it limits those deposits to less than the IRS maximum. Many plans do not offer them. Plain Roth deferrals and the ordinary backdoor Roth through an IRA are separate ideas: backdoor Roth pro-rata calculator.

Is it worth it?

It moves up to $47,500 a year into a tax-free account that has no required minimum distributions, at the price of no deduction now. Whether you are better off putting that money in a taxable account, or converting traditional money in a low-bracket year instead, depends on your brackets, your Medicare surcharge tiers and the years ahead: Roth conversion calculator, your 401(k) maximum. Conversions and distributions are reported on Form 1099-R: see Form 1099-R explained.

Paid tool The mega backdoor moves new money into Roth; the larger lever for most savers is the traditional balance already there, and which years to convert it in. The Roth Conversion Planner works out how much to convert in each year from now to your plan end age: the federal and state tax each conversion costs, the IRMAA tier that year’s MAGI sets two years later, and the ACA subsidy it affects — beside the same years with no conversions, and downloadable as a PDF you keep. A planning tool, not advice: the numbers move when your assumptions do. Build my conversion schedule — Personal PRO ($49) → Roth Conversion Planner: see what is included, and price this year free, first →

A mega backdoor Roth moves money into Roth now; how much traditional money to convert as well, and when, is a multi-year tax question. QuantCalc runs the whole retirement — contributions, conversions, taxes, Medicare surcharges — year by year.

Run the free tax-aware simulation →

Common questions

How much can I put into a mega backdoor Roth in 2026?

The overall limit of $72,000 minus your own deferral and the employer’s contributions (IRC §415(c)). With a $24,500 deferral and $10,000 from your employer that is $37,500; with no employer money, $47,500.

Do catch-up contributions count toward the overall limit?

No. Catch-ups are on top of the $72,000 overall limit, so at ages 60 to 63 up to $83,250 can go in (IRS Notice 2025-67).

Does my plan allow a mega backdoor Roth?

Only if it accepts after-tax deposits and lets you convert them to Roth in the plan or take them out in service. The IRS limit does not make the plan offer it; check the summary plan description or ask the administrator.

Are the earnings on after-tax contributions taxed?

Yes, when converted or withdrawn, unless you convert before they build up. Notice 2014-54 lets the after-tax part of a split payment go to a Roth IRA and the pre-tax part to a traditional one (IRS Notice 2014-54).

What happens to the converted money?

It is Roth money. For a Roth IRA the rules on qualified withdrawals apply (Pub. 590-B); see Roth IRA rules 2026.

Sources

Related

Max 401(k) contribution 2026 → 401(k) contribution limits 2026 → Backdoor Roth calculator → Roth IRA rules 2026 → Roth IRA calculator → Roth conversion calculator → Catch-up contributions 2026 → Form 1099-R explained →