Mega Backdoor Roth Limit for 2026: How Much After-Tax Room You Really Have

By Kevin Luu, Co-Founder and Chief Learning Officer. Reviewed on 2026-09-30.

For 2026, the mega backdoor Roth limit is $72,000 minus your own 401(k) deferrals minus your employer’s contributions. That $72,000 is the IRS cap on total “annual additions” to one person’s 401(k) under Internal Revenue Code section 415(c). If you defer the full $24,500 and your employer adds $9,000, you have up to $38,500 of after-tax room you can convert to Roth, provided your plan allows it.

For earlier years, the same math used $69,000 and $23,000 (2024) and $70,000 and $23,500 (2025), per the IRS cost-of-living table. Those years are closed now; 2026 is the year you can still act on.

The 2026 numbers that set your mega backdoor room

Source for all five: IRS Notice 2025-67. Catch-ups are excluded from the 415(c) limit by IRC section 414(v)(3)(A).

One limit is not on this table on purpose. The Roth IRA contribution limit ($7,500 for 2026) has nothing to do with the mega backdoor. That is the “regular” backdoor Roth IRA, a separate move you can do in the same year. People searching for a “mega backdoor IRA limit” are usually mixing the two up. When after-tax 401(k) money is rolled to a Roth IRA, the rollover does not count against the $7,500.

Why this matters more for a California or Washington W-2 family

A household earning $750,000 to $3 million is phased out of direct Roth IRA contributions (the 2026 married-filing-jointly phase-out is $242,000 to $252,000). For most of these families the 401(k) is the only place large amounts of Roth money can go each year. If both spouses’ employers offer the feature, each spouse has a separate $72,000 limit, so a couple can move roughly twice the single-plan amount (about $77,000 for 2026 if both plans look like the one in the example below), depending on each plan’s match and after-tax cap.

The alternative for that money is usually a taxable brokerage account. In California, there is no lower rate for long-term capital gains, so gains and dividends are taxed as ordinary income at up to 13.3% (the 2025 top rate, which applies to taxable income over $1 million; FTB), on top of the federal 20% long-term gains rate and the 3.8% Net Investment Income Tax. Roth growth avoids all of that if withdrawals are qualified.

In Washington, there is no tax on wages today, but long-term capital gains above the standard deduction ($278,000 for 2025, the latest published) are taxed at 7%, and 9.9% on taxable gains above $1 million (WA DOR). Retirement accounts are exempt. Washington has also enacted a 9.9% income tax for individuals and joint filers with adjusted gross income over $1 million, effective January 1, 2028 (WA DOR), which is relevant for the higher earners in this group when weighing future taxable income against Roth money.

How the mega backdoor works, step by step

1. Max your normal deferral. $24,500 for 2026, pre-tax or Roth 401(k).
2. Count the employer money. Match, true-up and profit-sharing all use up the $72,000.
3. Add after-tax (non-Roth) contributions through payroll, up to the remaining room or the plan’s own cap, whichever is lower. Many plans cap after-tax at a percentage of pay.
4. Convert quickly. Either an in-plan Roth conversion or an in-service rollover to a Roth IRA. Any earnings between contribution and conversion are taxable at conversion, so plans with automatic daily conversion keep that close to zero.

There is no April deadline here. Unlike an IRA, after-tax 401(k) contributions go in through payroll, so they must come out of paychecks during the plan year (for most plans, the calendar year). If you start in October, your room for the year is whatever the remaining paychecks can hold.

Worked example: a $950,000 Bay Area household

Assumptions, for illustration only: one spouse earns a $300,000 base at a large tech employer plus RSUs; the other is a physician whose hospital plan has no after-tax option. The tech plan matches 50% of the first 6% of base pay and allows after-tax contributions with automatic in-plan Roth conversion. Both under 50. Total household W-2 income is about $950,000.

Now compare 10 years of $38,500 a year in Roth versus a taxable account, assuming 6% annual growth. Both end near $507,000, with about $122,000 of that being growth. If the taxable account were sold after 10 years, with all growth taxed as long-term gains at 23.8% federal (20% plus the 3.8% Net Investment Income Tax) plus California’s 11.3% bracket and the 1% Behavioral Health Services Tax on any taxable income over $1 million (2025 California schedules, the latest published), the tax would be roughly $43,000 to $44,000. (California’s top 13.3% rate applies only at higher incomes than this household’s.) The Roth, if withdrawals are qualified, owes nothing. (This is simplified: in reality the brokerage account would also pay tax on dividends every year, so the gap is likely larger.) A Washington family in the same spot would pay the federal 23.8%, and Washington’s 7% only on gains above that year’s standard deduction.

The cost of the strategy is cash flow, not tax. The $38,500 comes out of after-tax pay. For a family also funding a 529, a nanny and a Bay Area mortgage, the real decision is whether that cash is better spent here or kept liquid.

The decision your family actually has to make

• Does the plan allow it? Check the summary plan description for “after-tax contributions” and “in-plan Roth conversion” or “in-service distributions.” No feature, no mega backdoor.
• Is cash flow covered first? Emergency reserve, RSU-related tax bills, childcare and 529 goals usually come before locking more money into a retirement account.
• Which spouse’s plan? If only one plan offers it, that plan carries the strategy. If both do, each person gets their own $72,000 limit.
• Job change mid-year? The 415(c) limit applies per unrelated employer plan, but the $24,500 deferral limit is per person across all plans. Coordinate before your last paycheck at the old job.

Mistakes we see with high-earning W-2 families

• Waiting months to convert. Growth on unconverted after-tax money becomes taxable. Use automatic conversion if the plan offers it.
• Front-loading deferrals and losing match. If you hit $24,500 by spring and your plan has no true-up, you may miss match on later paychecks. That match also changes your mega backdoor room.
• Assuming the full amount is safe. After-tax contributions are part of the plan’s nondiscrimination (ACP) testing. If the plan fails, highly compensated employees can have some contributions refunded after year-end.
• Forgetting the catch-up rule. If you are 50 or older and your 2025 FICA wages from this employer exceeded $150,000, your 2026 catch-up must be Roth. Catch-ups do not reduce mega backdoor room.

Roth 401(k) money and Roth IRAs have no lifetime required minimum distributions for the owner (IRS RMD FAQs), which makes Roth dollars useful money to leave to children. For withdrawal timing and the five-year rules, see our guides on mega backdoor Roth withdrawal rules and when you can withdraw from a Roth IRA.

What to write down for your kids

Your children will not see the payroll elections. They will see, decades from now, a Roth account with a balance. What helps them is a one-page note: why you chose Roth over brokerage, what cash you gave up to do it, and what you would want the money used for. As Kevin Luu puts it: “Your kids don’t need to inherit your portfolio. They need to inherit your decision-making process.” A FamilyKnowledge® entry like this takes 20 minutes and is the kind of record that makes an inheritance usable.

Frequently asked questions

What is the maximum mega backdoor Roth contribution for 2026?

In theory, $72,000 minus your deferrals and employer contributions. If you contributed nothing else and got no match, that is $72,000, but in practice most people defer $24,500 first, leaving $47,500 before any match. Your plan may cap after-tax contributions lower, so the plan document sets your real maximum.

Can I do a backdoor Roth IRA and a mega backdoor Roth in the same year?

Yes. They are separate. The backdoor Roth IRA uses the $7,500 IRA limit for 2026 and depends on the pro rata rule if you hold pre-tax IRA money. The mega backdoor runs through your 401(k). See how the pro rata rule works.

Is the mega backdoor always better than investing in a brokerage account?

Not always. Brokerage money is available any time and can fund a home purchase or a sabbatical without penalty. For families who will need the cash within a few years, liquidity can matter more than tax-free growth. We compare the two in mega backdoor Roth vs brokerage.

Next step

Pull your 401(k) summary plan description this week and search it for “after-tax” and “Roth conversion.” If both appear, calculate your 2026 room with the table above and set the payroll election before the next pay cycle. If you want this coordinated with RSU taxes and the rest of your benefits, our retirement and employee benefits and tax management work at Age Five Family Office™ starts with a Tax & Wealth Assessment.

This is general education, not individual advice. The right move depends on your family’s full picture.

Written by

Kevin Luu

Co-Founder and Chief Learning Officer, Bright Advisers

Kevin has advised high-income W-2 tech and biotech families since 2015, and leads the education-first Age Five Family Office from Brea, California.

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