With the IRS raising the 401(k) employee deferral limit to $24,500 for 2026, up from $23,500 in 2025, it’s important to remember that a $1,000 increase deserves more than a shrug, and two other limit changes this year deserve far more attention than they are getting.
The Three Numbers That Actually Matter in 2026
Ultimately, the $1,000 increase in the base deferral limit sounds modest, but when you compound this 7% annually over 10 years, that extra $1,000 per year produces roughly $13,800 in additional retirement assets. Meaningful, but not the headline.
The catch-up contribution for workers aged 50 and older also increased, from $7,500 in 2025 to $8,000 in 2026, bringing the total that an over-50 worker can defer to $32,500. Over 10 years at 7%, maxing that out produces approximately $449,000. Keep in mind that if your 2025 FICA wages exceeded $150,000, the IRS now requires these catch-up dollars to be made on a Roth (after-tax) basis, meaning you’ll skip the immediate tax break, but your future withdrawals, and all that compound growth, will be entirely tax-free.
The real story is the SECURE 2.0 super catch-up for workers aged 60 through 63, which (again) has a limit of $11,250 in 2026, replacing the standard catch-up for those four years. Combined with the base deferral, someone in that window can contribute up to $35,750 this year. Ten years of maxing it out at 7% yields roughly $494,000, about $45,000 more than the standard 50-plus path over the same period.
If you turned 60, 61, 62, or 63 this year and are not hitting $35,750, you are leaving behind the most generous contribution window Congress has ever created for pre-retirees.
The Ceiling Most High Earners Have Never Heard Of
The total additions limit under IRC Section 415(c) rose from $70,000 in 2025 to $72,000 in 2026. This caps all contributions to a defined contribution plan in a single year: employee deferrals, employer contributions, and after-tax contributions combined.
For most W-2 employees, the 415(c) limit is invisible because their employer match does not push them near it. For self-employed individuals, business owners with solo 401(k)s, or employees in plans that allow after-tax contributions, this is the real ceiling. A business owner who contributes $24,500 as an employee and makes a profit-sharing contribution of $47,500 brings the total to exactly $72,000. Every dollar above that amount is a risk of plan disqualification.
The mega backdoor Roth works within this framework: contribute after-tax dollars up to the $72,000 total limit, then convert those funds to Roth. Most plan documents do not allow it, so confirm whether your plan permits after-tax contributions, in-service withdrawals, or in-plan Roth conversions.
The Tax Trap Hiding Inside a Larger Balance
Every dollar deferred into a traditional 401(k) today will be taxed as ordinary income when withdrawn. For someone already on Medicare, those withdrawals are included in the income calculation used to determine IRMAA surcharges added to Medicare Part B and Part D premiums.
In 2026, the standard Part B monthly premium is $202.90. Cross the first IRMAA threshold at $109,000 in modified adjusted gross income for single filers, and that premium jumps to $284.10 per month, nearly $975 more per year, triggered by a single dollar of income above the line. The SSA uses a two-year lookback, so a large 401(k) withdrawal or Roth conversion in 2026 affects your 2028 Medicare premiums.
A retiree in the 22% federal bracket who inadvertently crosses the IRMAA threshold can face a combined effective marginal rate approaching 40% on the dollars that push them over. The decision between maximizing traditional 401(k) contributions and redirecting savings to a Roth account is both a question of future tax rates and a question of Medicare costs.
Who Should Fill the Gap and Who Should Redirect
- Ages 60 to 63 with earned income and a balance below $1 million: Max the super catch-up first. The $35,750 ceiling disappears after age 63, and the tax deferral on that amount compounds for decades. This window is time-limited, and the math strongly favors using it.
- High earners with large traditional 401(k) balances are already on track to generate significant RMDs: Additional deferrals may be adding fuel to a future tax fire. If projected RMDs at age 73 will push you into the 24% bracket or above the IRMAA threshold, redirecting new savings to a Roth IRA or Roth 401(k) reduces that future exposure. The 2026 Roth IRA contribution limit is $8,000, including the catch-up for those 50 and older.
- Business owners and solo 401(k) holders: Confirm whether your plan allows after-tax contributions. The 415(c) limit of $72,000 creates room to contribute far beyond the employee deferral cap. If your plan document permits it, the mega backdoor Roth is the most efficient tax-free compounding vehicle available outside of a health savings account. If your combined income already exceeds the first IRMAA threshold at $109,000, the tax planning around these decisions alone justifies a session with a fee-only advisor.
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