Mega Backdoor Roth: Is It Worth It on an Executive Salary?

What happens if your plan accepts after-tax dollars above the $24,500 deferral?

The 401(k) deferral limit for 2026 is $24,500 for employees under 50. Most people stop counting there. The IRS total limit for 2026 under section 415(c) is $72,000, which counts your employee deferral, your employer's contribution (usually a match), and after-tax deposits all together.

If your plan offers after-tax deposits, that slot fills the room left over after the first two. Catch-up contributions at 50 and above sit outside this $72,000 limit, so they don't shrink the after-tax room.

Your plan must offer two separate features before after-tax deposits make sense. First, it must accept after-tax contributions. Second, it must allow either an in-plan Roth conversion, automatic or manual, or an in-service withdrawal that moves the after-tax money out to an IRA. Plenty of plans offer the first feature and not the second. Check the summary plan description, or put the question to the plan's recordkeeper directly. Does it convert after-tax deposits, or does it only accept them and let them sit as non-taxable money for years? The answer changes every number on this page.

Another belief worth checking: Roth money is tax-free money. Actually, your after-tax deposits come out of pay that has already been taxed. You get no deduction for them, so when you convert them to Roth, the contributions themselves are never taxed again. But any earnings that built up inside the after-tax subaccount while it sat as pre-conversion money are taxable income in the year you convert. A $37,000 after-tax deposit that earned $1,000 over the year means you owe tax on that $1,000 when converted, not on the original $37,000.

One more constraint that many plans face: the ACP nondiscrimination test. The IRS requires that highly paid employees cannot contribute meaningfully more after-tax money than average or low-paid employees in the plan. If the test fails, after-tax contributions are refunded—usually in the first months of the following year—as taxable earnings plus your returned contributions. This happens automatically; you don't have a choice. Ask your plan administrator whether the plan passed its ACP test last year and whether after-tax deposits were refunded. If refunds have happened before, they might happen again.

In your 40s, with shares vesting every year

Meera, 44, works as general counsel at a public payments company and holds $900,000 in vested shares with about $300,000 vesting annually (hypothetical, round numbers). She supports her widowed mother and is bound by a three-times-salary ownership guideline—$400,000 salary times three equals $1.2 million required. Her current holdings are $900,000, so she cannot sell vested shares to backfill lost pay without falling short of her guideline.

Her 401(k) math: she defers the $24,500 maximum, and her employer adds a $10,500 match. The after-tax room is $72,000 − $24,500 − $10,500 = $37,000. Spread over 26 paychecks, that's about $1,423 per check, or roughly $3,083 less take-home pay each month. Her situation is typical for executives in concentrated stock: the room is large, but the cash cut is real, and share sales aren't always an option.

Why the cash flow matters is in the next fifteen years. Assume 5 percent a year, for illustration. If Meera contributes $37,000 annually and converts it to Roth each year, that money compounds tax-free inside the Roth. By age 59, she will have contributed about $555,000 and the balance will have grown to about $800,000. Starting at 60, a 4 percent withdrawal is about $32,000 annually, roughly $2,667 monthly, tax-free once the five-year holding period is met. That tax-free paycheck is valuable in a year when her other income spikes, or when she waits to claim Social Security and her income is otherwise low.

The tax bill arrives this year. When Meera converts after-tax money to Roth, she owes federal income tax on the earnings that converted with it. In the first year, suppose the subaccount earned $800 on the $37,000 after-tax contribution. She pays federal tax on that $800 only, not the full $37,000, at her marginal rate. At 37 percent, that's about $296. State income tax may apply to those earnings too, but FICA does not apply to a conversion. The bigger cost is cash: the after-tax deposit cuts her take-home pay by about $3,083 a month, close to $37,000 over the year, and none of it comes back until retirement. She is betting that tax-free Roth withdrawals at 60 and later will outweigh that wait.

Here is the trade-off with deferred compensation. With the same $37,000, Meera could instead fund a nonqualified deferred compensation plan offered by her employer. She defers pre-tax income, pays no federal tax on it this year, and the take-home cut is smaller: about $23,310 for the year ($37,000 × (1 − 0.37)), or roughly $1,943 a month. She avoids the immediate tax bill, and the money grows tax-deferred on the company's books. When she withdraws it in retirement, the full amount is taxed as ordinary income. If her bracket falls below 37 percent by then, she might pay less tax in total, so the choice depends on whether she expects a higher rate now or at withdrawal. Meera already holds $900,000 of employer stock. Adding to the employer's unsecured promise (deferred comp is backed only by the employer's creditworthiness, not held in trust) is usually reason to lean Roth. The full comparison between deferred comp and 401(k) savings is covered in the firm's guide to NQDC planning.

Watch the chart below. The Roth route costs $13,690 more in federal tax this year but leaves nothing exposed to the company's credit. The deferred comp route cuts the immediate tax bill but is entirely dependent on the employer staying solvent. Markets can fall, and the projected $800,000 balance could be lower or even below what Meera contributed; the takeaway is to assume returns are uncertain.

If your take-home pay already supports a parent

The maxim 'fund every account available' doesn't fit Meera. She sends money to her mother each month, holds shares she cannot sell, and has irregular expenses from her mother's care. Funding the full $37,000 after-tax room would cut her monthly pay by $3,083. That might force her to pause in the middle of the year, let the after-tax subaccount sit unconverted while earnings pile up, or drain her liquid savings. Instead, she might contribute $18,500—half the room—and convert that each quarter. That cuts take-home pay by about $1,542 monthly, which her budget absorbs. This is a judgment call. We'd lean toward the smaller, steady amount over a partial year of contributions followed by a gap. An irregular contribution stream is what causes after-tax money to sit unconverted, and that is where the tax bill sneaks upward.

When you turn 50, does a catch-up shrink the mega backdoor Roth room?

No. The catch-up contribution sits outside the $72,000 limit. For 2026, the catch-up is $8,000 at age 50 and above, and $11,250 at ages 60 to 63. If Meera defers $24,500 plus the $8,000 catch-up ($32,500 total) and her employer adds $10,500, only the $24,500 counts toward the $72,000 limit.

Her after-tax room stays $72,000 − $24,500 − $10,500 = $37,000. Her total into the plan can reach $80,000. At ages 60 to 63, with the $11,250 catch-up, the room is still $37,000 and her total can reach $83,250.

One detail that changes the story: if your prior-year FICA wages exceeded $150,000, your catch-up contributions must be Roth. You cannot defer them pre-tax. That covers almost every executive in this situation. From the year you turn 50, the catch-up alone adds $8,000 a year of Roth money, or $11,250 at 60 to 63, even if you never touch the after-tax slot. That steady Roth stream makes the after-tax decision less critical in your 50s.

What happens to the Roth money once the paychecks stop?

Roth accounts in employer 401(k) plans no longer have lifetime required minimum distributions. Before this rule changed, you had to start drawing Roth 401(k) money at age 73 (age 75 for people born in 1960 or later), whether you needed it or not. Now you don't.

You can leave it untouched and let it grow, or withdraw it at any time. Once you are 59½ and the five-year holding period is met, withdrawals are qualified and completely tax-free.

The withdrawal order matters for cash flow. In Meera's early retirement years, before Social Security starts, she should draw first on her taxable investment accounts and any deferred compensation installments. Save Roth withdrawals for high-income years, such as a late bonus or a spouse's peak earnings. Roth withdrawals don't add to taxable income, so they won't push her into a higher bracket or raise the MAGI that sets her Medicare IRMAA two years later. Used this way, the Roth is the account Meera taps when every other dollar would be taxed at 37 percent.

For heirs, the rules depend on who inherits. Meera's widowed mother is older than Meera, which makes her an eligible designated beneficiary. She can inherit the Roth 401(k) as a separate beneficiary IRA and take required distributions spread over her own life expectancy. Those withdrawals remain tax-free if the five-year holding period was met. If Meera marries, a surviving spouse may roll the account into a spouse IRA and handle it as their own. Most other beneficiaries, such as an adult child or a sibling, generally must empty the account within ten years, though every dollar they take out is tax-free.

Questions for the plan administrator before your first after-tax paycheck

Ask these questions before you direct payroll to start after-tax contributions. The first set goes to your plan administrator; the second to your CPA; the third to Scotia Wealth Management or your advisor.

Treating the after-tax subaccount like an ordinary tax-deferred account and planning to convert 'someday' after retirement costs real money. The belief sounds safe: after-tax money grows tax-deferred, so wait until you retire and your bracket may be lower. But the longer earnings compound inside the subaccount before conversion, the larger the tax bill when you finally convert. Assume 5 percent a year, for illustration. If Meera contributes $37,000 annually for ten years without converting, that grows to about $465,000. Of that, roughly $95,000 is earnings. Converting at the 37 percent federal rate, she pays about $35,000 in tax on those earnings alone. Had she converted each year, she would have paid tax on maybe $800 to $2,000 in annual earnings, spread across ten years. The compounding earnings are what turn a small tax bill into a large one.

When Scotia Wealth Management reviews an existing 401(k), if automatic conversion is already running and the conversion dates on the statements match the contribution dates, the firm leaves it alone. If after-tax money has piled up unconverted for months or years, Scotia Wealth Management discusses whether to convert it now—and pay the tax on accumulated earnings—or hold for a lower-income year. This is where the second opinion works: an existing advisor might have set up automatic conversion without checking whether it fits the client's cash flow. Scotia Wealth Management estimates the monthly take-home cut, looks at the ownership guideline, and makes sure the contribution is sustainable.

• Does the plan convert after-tax deposits to Roth automatically each paycheck, or only when you request it?
• Does payroll stop after-tax deposits when the $72,000 total is reached, or does it continue and leave you to track the limit?
• Did the plan pass its nondiscrimination test last year, or were after-tax contributions refunded?
• How will in-plan Roth conversions appear on my January Form 1099-R—will they show separately from pre-tax deferrals?
• If I leave this employer, what happens to unconverted after-tax money still in the plan?
• How does the monthly take-home cut interact with my ownership guideline and share vesting schedule?

Bringing the plan summary to Scotia Wealth Management

The right time to review this decision is before the next payroll election window or after a raise changes your employer match. Bring the summary plan description, a recent pay stub showing gross pay and all deductions, your latest 401(k) statement with the after-tax subaccount balance clearly shown, and the letter describing your ownership guideline. Scotia Wealth Management works out your room, calculates the monthly take-home cut, and fits it against your concentrated stock holdings and cash needs. If the plan doesn't offer in-plan conversion or in-service withdrawals, the firm tells you straight: the after-tax slot isn't usable for a mega backdoor Roth without a workaround. If the plan passed the ACP test but refunds after-tax contributions some years, Scotia Wealth Management notes that variability and builds a lower expected contribution into the plan.