Don Lair

Wed, September 2, 2026 at 6:25 AM EDT 5 min read

Quick Read

• Starting in 2026, employees 50+ earning over $150,000 must route all catch-up contributions to Roth 401(k), erasing up to $2,700 in annual federal tax deductions.

• Only 24% of Vanguard plans allow voluntary after-tax contributions and just 36% offer in-plan Roth rollovers, making the mega backdoor Roth inaccessible for most workers.

• IRS Actual Contribution Percentage testing can force taxable refunds of after-tax contributions back to high earners when too few rank-and-file employees participate in the feature.

• Read More: Learn 7 ways to generate income with a $1,000,000+ portfolio (sponsor)

High earners spent 2025 running a familiar arithmetic: max the pretax 401(k), max the catch-up, then layer voluntary after-tax dollars up to the overall defined contribution ceiling and convert. That math no longer describes 2026. Starting January 1, 2026, employees age 50 and older who earned more than $150,000 in 2025 must direct any catch-up contribution into a Roth 401(k) rather than a pretax account. The threshold was originally set at $145,000 and is adjusted annually for inflation. Status is determined by Box 3 of the 2025 W-2, and 1099 side-gig or K-1 partnership income does not count.

That single change reshapes the mega backdoor Roth calculus. Tom O'Saben of the National Association of Tax Professionals told the New York Times the shift "may come as a surprise" to taxpayers who relied on catch-up contributions as a late-career tax-cutting strategy. A 55-year-old in the 24% bracket making the $8,000 catch-up under the old rules would have cut federal tax by roughly $1,900; a 62-year-old making the $11,250 super catch-up would have cut it by roughly $2,700. Those deductions are gone for higher earners, and that lost cash flow is exactly what many households used to fund the after-tax bucket.

Prerequisites Most Plans Still Fail

The mega backdoor Roth is an employer-plan maneuver that operates under the overall defined contribution limit at the plan level, distinct from any IRA-level workaround. Two plan features are required, and readers should confirm both with their plan administrator in writing:

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