Mega Backdoor Roth: After-Tax 401(k) Contributions and In-Plan Conversions

A mega backdoor Roth uses after-tax contributions to a 401(k) plan, then moves that money into a Roth account, either inside the plan or out to a Roth IRA. It can put significantly more money into Roth savings each year than IRA contribution limits allow.

This guide is for workers whose plan accepts after-tax contributions and who already max out salary deferrals, often high income earners whose direct Roth contributions are phased out. It matters because the mega backdoor Roth strategy uses room under the IRS total limit that most savers leave empty.

Sources: IRS Notice 2025-67 (2026 limits), IRS guidance on rollovers of after-tax contributions (Notice 2014-54), the IRS designated Roth account FAQs, and Pub 590-A.

A small glass jar of coins beside a much larger, fuller glass jar of coins and a cloth-bound notebook with a brass pen on a wooden desk, suggesting a mega backdoor Roth adding more Roth savings.
A mega backdoor Roth adds room for tax-free growth beyond IRA limits.

What is a mega backdoor Roth?

A mega backdoor Roth is not an account type. It is a two-step mega backdoor strategy inside a workplace retirement plan such as a 401(k):

  • Step 1: make after-tax contributions on top of your pre-tax or Roth salary deferrals.
  • Step 2: move that money to Roth, through in-plan Roth conversions or an in-service distribution rolled over to a Roth IRA.

Because the money often lands in a Roth IRA, some call it a mega backdoor Roth IRA. After the conversion, earnings grow tax free, and qualified, tax-free withdrawals follow in retirement. Those are the tax benefits: tax-free retirement savings beyond normal limits.

After-tax contributions vs Roth 401(k) contributions

People often confuse after-tax contributions with Roth 401(k) contributions. Both use after-tax dollars, but the IRS rules differ.

Roth 401(k) contributions, also called designated Roth contributions, are elective salary deferrals. They share the 402(g) deferral limit with pre-tax deferrals, and qualified distributions, earnings included, are tax free.

Non-Roth after-tax contributions are not deferrals and do not count toward that limit. You get no tax deduction for them, and their earnings are pre-tax until converted, so you pay taxes on those earnings when they are withdrawn or converted.

Coins spilling from an open kraft envelope toward a small open wooden box beside a fountain pen on a dark desk, suggesting after-tax contributions going into a retirement plan.
After-tax contributions come from take-home pay and get no deduction.

2026 contribution limits for a mega backdoor Roth

Two 401(k) contribution limits in IRS Notice 2025-67 define the 2026 space for a mega backdoor Roth:

  • Salary deferrals (section 402(g)): $24,500, covering pre-tax and Roth 401(k) contributions combined.
  • Total annual additions (section 415(c)): $72,000, or 100% of compensation if less. This counts deferrals, employer contributions, and after-tax contributions.
  • Catch-up contributions: $8,000 at age 50 or older, or $11,250 at ages 60 through 63.

Catch-up contributions sit on top: the IRS lists $80,000 including the standard catch-up, or up to $83,250 at ages 60 to 63. They add no after-tax room; the mega backdoor Roth strategy works only under $72,000.

Three plain wooden blocks of rising height, each topped with a short stack of coins, beside a folded blank sheet and reading glasses, suggesting layered 401(k) contribution limits.
In 2026, deferrals, employer contributions, and after-tax contributions share a $72,000 limit.

Roth catch-up contributions for higher earners

If your 2025 wages from the employer sponsoring the 401(k) topped $150,000, your 2026 catch-up contributions in that employer sponsored plan must be Roth 401(k) contributions.

How much can you put in a mega backdoor Roth?

Start with $72,000, subtract your salary deferrals, then subtract employer contributions. What is left is the most you could add as after-tax contributions, if your plan allows that much.

Example (illustrative): a 45-year-old defers $24,500 in 2026, and the employer adds $8,000 in matching contributions. The room left is $72,000 − $24,500 − $8,000 = $39,500. If the plan accepts it, all $39,500 could become Roth savings.

Your plan may set a lower cap. When the employer contributes more, your room shrinks, because profit sharing contributions and matches count toward the same $72,000.

How the mega backdoor Roth strategy works, step by step

Step 1: Check plan rules and plan documents

Not all plans offer these features. Read the summary plan description and other plan documents, or ask the plan administrator, about three plan rules:

  • Making after-tax contributions above the deferral limit.
  • In-plan Roth conversions, which the IRS calls in-plan Roth rollovers, or in-service distributions.
  • How often the plan permits conversions or in-service withdrawals.

The IRS says 401(k), 403(b), and governmental 457(b) plans with designated Roth accounts may offer in-plan Roth rollovers, and each plan can specify which amounts qualify and how often.

A closed navy binder with reading glasses on top, a pencil, and a tray of paper clips beside a coffee cup on a light desk, suggesting a review of 401(k) plan documents.
Your plan documents say whether after-tax contributions and conversions are allowed.

Step 2: Start making after-tax contributions

Set a payroll election once your pre-tax or Roth deferrals are planned. Making after-tax contributions each pay period and converting soon after keeps taxable earnings small; the mega backdoor Roth strategy rewards speed.

Step 3: Complete the Roth conversion

Your plan rules decide which of two routes you can use.

In-plan conversion. The money moves into the plan’s designated Roth account. The taxable amount is fair market value minus your basis, so only earnings are taxed. The IRS says no withholding is required on an in-plan Roth direct rollover, and the move cannot be recharacterized.

In-service distributions to a Roth IRA. If the plan allows in-service distributions, you can roll the after-tax amounts to a Roth IRA. Under Notice 2014-54, when one distribution goes to more than one destination, pre-tax earnings can go to a traditional IRA and the after-tax basis to a Roth IRA.

The IRS also says a partial distribution generally carries a pro rata share of the account’s pre-tax amounts, so ask how your plan tracks the after-tax portion.

Two brass-cornered wooden boxes side by side with a few coins on the desk between them and more coins in the open right box, suggesting an in-plan Roth conversion between accounts.
An in-plan Roth conversion moves after-tax money to the plan’s Roth account.

Tax implications and tax timing

Contributions already taxed are not taxed again at conversion; only the earnings face income tax. Wait a year to convert and you owe income tax on that year’s growth.

Converted earnings are ordinary income for the year of the conversion. The IRS notes you may need more withholding or estimated payments to avoid an underpayment penalty, one of the tax consequences to plan for.

Five-year rules for Roth assets

A qualified, tax-free distribution from a designated Roth account requires five taxable years since your first designated Roth contributions to that plan, plus age 59½, death, or disability. Then the money is withdrawn tax free.

If the plan pays out in-plan rollover amounts within five years, the taxable part can face the 10% early withdrawal tax unless an exception applies; see IRA early withdrawal exceptions. And when you roll a designated Roth account into a Roth IRA, time spent in the plan does not count toward the Roth IRA’s five-year period.

Mega backdoor Roth vs backdoor Roth IRA

What is the difference between a backdoor Roth and a mega backdoor Roth? The regular backdoor Roth is an IRA move: a nondeductible traditional IRA contribution, then a backdoor Roth IRA conversion. It is capped by IRA contribution limits, $7,500 for 2026 ($8,600 at 50 or older), and the pro rata rule counts your traditional IRA, SEP, and SIMPLE balances. Our backdoor Roth IRA guide covers it.

The mega backdoor Roth IRA route runs through employer plans instead, such as a 401(k) retirement plan. It can move tens of thousands of dollars a year if your plan offers the features. Unlike IRAs, employer plans set their own rules, and someone eligible for both can do each in the same year.

High income earners and the mega backdoor Roth

Can I make a backdoor Roth if I make $500,000 a year? Yes. No income limits apply to after-tax 401(k) contributions or to conversions at any income level; the income cap on conversions was repealed for tax years after 2009.

Income limits on direct Roth contributions

Direct Roth IRA contributions do have income restrictions. For 2026, eligibility phases out between $153,000 and $168,000 of modified adjusted gross income for single filers, and between $242,000 and $252,000 for married filing jointly. Above those ranges, Roth IRA contributions are not allowed.

Highly compensated employees and plan testing

The practical limit for highly compensated employees is testing. After-tax and matching contributions both count in the 401(k) ACP nondiscrimination test. If a plan fails and corrects by refund, excess contributions, adjusted for earnings, are paid out to highly compensated employees. For 2026, the pay threshold in that IRS definition stays at $160,000.

Roth 401(k) or Roth IRA: where the money ends up

Inside the plan, converted money keeps its tax-free growth in the Roth 401(k) account but follows the plan’s investment menu, fees, and distribution rules. Under current rules, designated Roth accounts have no required minimum distributions during the owner’s lifetime, the same as Roth IRAs.

Rolling it out to a Roth IRA brings IRA investment choices and ordering rules, which suits some mega backdoor Roth IRA savers. Our Roth IRA guide explains those withdrawals, and Roth IRA vs 401(k) compares the two accounts.

Is the mega backdoor Roth still allowed in 2026?

Yes, under current IRS rules. IRS guidance on after-tax rollovers and in-plan Roth rollovers still applies, along with the 2026 limits above. Tax laws change and employers drop features, so confirm with your plan administrator.

Is there a downside to a mega backdoor Roth?

  • Availability: not all plans allow after-tax contributions, in-service distributions, or in-plan conversions.
  • Testing: highly compensated employees may see contributions capped or refunded.
  • Taxes on earnings: delay the conversion and growth becomes taxable.
  • Cash flow: the money comes out of take-home pay with no tax break today.
  • Complexity: payroll elections, conversion requests, and tax forms have to line up.

The mega backdoor Roth strategy tends to fit savers who already max out deferrals and can contribute significantly more. For many, the employer match and a regular Roth IRA come first.

Reporting and records

Your plan reports in-plan Roth rollovers and distributions on Form 1099-R. If you roll after-tax amounts to a Roth IRA, keep basis records under the Form 8606 instructions.

Where it fits in your retirement savings

A mega backdoor Roth IRA plan is one retirement savings strategy among several. For how a single IRA conversion is taxed, see our Roth conversion guide. Retiring early? See the Roth conversion ladder and 72(t) SEPP. For the wider picture, see retirement tax strategy.

The bottom line: more tax-free retirement savings

A mega backdoor Roth turns after-tax 401(k) contributions into Roth savings, up to the $72,000 total for 2026, when your workplace retirement plan permits after-tax contributions and conversions. Check plan documents, convert promptly, and get tax advice from a tax professional or financial advisor.

Written by Tim Schmidt and reviewed for tax and account accuracy by Sean Webster, CPA. Last reviewed November 10, 2026 (America/New_York). This guide is for general education, not tax, legal, or investment advice, and not a recommendation to make a contribution or conversion. IRAInvesting.com is not a custodian, broker-dealer, plan administrator, tax preparer, or investment adviser. Talk with a licensed tax professional before you act, and confirm current limits on IRS.gov. Investing involves risk, including possible loss of principal.