The Mega Backdoor Roth Move Tech Workers Use to Stuff an Extra $34,000 a Year Into a Roth

A 38-year-old software engineer in the Bay Area earning $280,000 hits the standard $24,500 401(k) deferral by August. The next four months of contributions get redirected to a brokerage account, where every dollar of growth is taxed. There is a way to keep funneling another $34,000 per year into a Roth wrapper, and roughly one in three large tech employers already has the plumbing built in. Most participants never ask.

The mechanic hinges on the IRS code section nobody talks about at the kitchen table: 415(c). Most 401(k) coverage stops at the employee deferral limit. The 415(c) total annual additions limit is the real ceiling on what can land inside the plan, and for 2026 the IRS lifted it from $70,000 to $72,000. Everything between the deferral and that ceiling is the opening.

How the $34,000 Number Falls Out of the Math

Walk the stack for the engineer above. The $24,500 employee deferral lands first. A typical large-cap tech match runs 5% to 6% of base, which on a $280,000 salary gets capped quickly; assume the employer kicks in $13,500. That is $38,000 consumed against the $72,000 415(c) cap. The leftover space, $34,000, is exactly what the plan document can let the participant fund as after-tax (not Roth, not pre-tax) contributions.

Those after-tax dollars are useful only if they leave the after-tax bucket fast. Two routes do the job. An in-plan Roth conversion sweeps the after-tax balance into the Roth side of the same 401(k). An in-service rollover ships it to an outside Roth IRA. Either way, the basis converts tax-free, and from that moment forward the money grows and eventually distributes tax-free.

What 30 Years of Tax-Free Compounding Looks Like

Run the engineer’s $34,000 annual contribution out 30 years at a 7% return. The future value of that annuity stream lands at roughly $3.21 million, none of which the IRS gets to touch on the way out. That sits on top of the standard deferral, the match, and any taxable brokerage savings the household runs alongside.

The case for moving fast is sharper than usual. Core PCE inflation reached 129.28 in March, drifting up from 125.79 last May, and the 10-year Treasury is sitting around 4.4%. Every dollar of taxable interest now generates a real tax bill, which makes the tax-free wrapper measurably more valuable than it was when yields were near zero. The personal savings rate has slid to 4%, the lowest in two years, so any household at the high end of the income distribution that wants to actually accumulate wealth has to push more dollars into shelters.

Where the Strategy Quietly Breaks

Three traps. The plan has to permit both after-tax contributions and either an in-plan Roth conversion or in-service distribution. The summary plan description spells it out; HR usually will not volunteer it. Second, any earnings sitting on the after-tax balance at conversion time are taxable as ordinary income. Convert weekly or monthly if the plan allows, or batch at year-end if it only permits one rollover annually. Third, the 415(c) cap counts the employer match. A bigger match shrinks the after-tax room.

What to Do This Quarter

1. Pull the summary plan description from the benefits portal and search for the phrases “after-tax contributions” and “in-plan Roth rollover.” If both appear, the strategy is live; if either is missing, escalate to the plan sponsor before assuming it is unavailable.
2. Set the after-tax contribution rate to hit $34,000 across the calendar year, then enable automatic in-plan conversions if the recordkeeper offers them. Fidelity, Schwab, and Empower all support automatic sweeps on most large plans; the toggle is usually two clicks deep.
3. Verify the employer match figure on the most recent paystub before assuming $13,500 of 415(c) space is occupied. A richer match (true-ups, profit sharing, ESOP allocations) shrinks the after-tax window. Recompute the available room every January when the IRS publishes new limits.

The Federal Reserve has held the funds rate at 3.75% for five months, GDP growth printed 2% in the first quarter, and the political calendar is starting to pull tax policy back into focus. Locking in tax-free growth at today’s rates, while a plan document still allows it, is a decision that compounds for three decades.