October 2026 began with three year-end deadlines still open, each with its own timeline and consequences for delaying.
The remaining weeks of 2026 offer a window to adjust 401(k) contributions, evaluate a Roth conversion by December 31, and review Medicare coverage before the December 7 enrollment deadline.
All three have a tax or coverage outcome that locks in permanently once the calendar year turns.
Also Read: Retirees may be ignoring a Medicare blind spot before 2027
401(k) catch-up contributions erode with every uncorrected paycheck
The standard employee deferral cap for 2026 is $24,500, and workers 50 and older can add an extra $8,000 for a combined ceiling of $32,500. Workers aged 60 to 63 qualify for a larger catch-up of $11,250, lifting their total limit to $35,750, Mercer Advisors noted in its September 2026 analysis.
Contributions flow only through payroll, and a deferral change takes one full pay cycle to process. Every paycheck at the old rate forces the remaining checks to absorb a larger share of the gap.
Vic Conrad, financial adviser and founder of Pinnacle Financial Strategies, told the Pittsburgh Post-Gazette that catch-ups for high earners must be designated as Roth contributions, leading to a direct tax hit for those high earners.
<strong>People who fall in that category need to financially be prepared for a larger tax bill. Simply put, all else being equal, you’ll have more taxable income as a result of the change,</strong>
Workers 50 and older whose Federal Insurance Contributions Act (FICA) wages exceeded $150,000 in 2025 face a SECURE 2.0 mandate: all catch-up contributions must now route into a Roth 401(k).
The rule took effect January 1, 2026, Mercer Advisors reported, and workers below that threshold can still choose a pre-tax 401(k) or Roth.
SECURE 2.0 strips catch-up access from plans without a Roth option
The Roth catch-up provision for high earners has caught many workers off guard in their employer-sponsored retirement plans.
A high earner whose employer does not offer a designated Roth account loses the 2026 catch-up opportunity, according to Mercer Advisors.
Some employers have not yet amended their plans to include a Roth contribution feature, which leaves affected employees with no workaround.
Workers in their peak earning years who assumed they could max out pretax catch-ups may discover that their plan’s current structure blocks them.
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The 2025 Form W-2 shows eligibility in Box 3, which reports the Social Security wages the IRS allows employers to use when applying the Roth catch-up mandate.
Mercer Advisors recommended logging into the plan portal this week to confirm year-to-date deferrals and verify whether catch-up dollars are routing to the correct account.
Roth conversions face a hard December 31 cutoff
A Roth conversion moves pre-tax retirement assets into a Roth account, and the converted amount counts as ordinary taxable income for the year of transfer.
The conversion deadline for the 2026 tax year is December 31, with no extension available and no grace period from the IRS, Mercer Advisors confirmed.
With three-quarters of this year’s income data now on the books, most workers can project full-year income with enough accuracy to size the conversion this month.
The 2026 standard deduction shelters $32,200 for married couples filing jointly and $16,100 for single filers, which offers a starting point for gauging bracket headroom, the IRS Revenue Procedure 2025-32 showed.
Medicare exposure adds a second reason to run the numbers early.
A 2026 conversion affects your modified adjusted gross income (MAGI), which determines your 2028 Medicare premiums under the two-year lookback rule, Mercer Advisors noted.
Waiting until mid-December leaves almost no room to scale back when a late capital gain or year-end distribution arrives, Mercer Advisors cautioned.
Medicare open enrollment closes on a fixed December 7 deadline
Medicare’s annual enrollment period opens October 15 and closes December 7, 2026, giving beneficiaries a fixed 54-day window to compare plans for 2027, according to the Centers for Medicare and Medicaid Services (CMS).
The CMS projected that the weighted-average monthly Medicare Advantage premium will drop 16.5%, from $14.37 in 2026 to $12 in 2027.
Insurers must have sent enrollees an Annual Notice of Change (ANOC) by September 30, 2026, outlining 2027 premium, benefit, and formulary changes, the CMS ANOC submission requirements showed.
Kiplinger advised reviewing the ANOC before comparing plans on Medicare.gov, because coverage that worked in 2026 may cost more, or less, next year.
Which year-end window near-retirees should tackle first
Workers still on payroll should treat the 401(k) deferral correction as the most time-sensitive of the three deadlines, Mercer Advisors recommended in its year-end guidance.
It is the only window that narrows with each uncorrected pay cycle, and a Roth conversion can still be sized accurately in November 2026.
For near-retirees already off payroll, Mercer Advisors moved the Roth conversion to the top of the list, since its December 31, 2026, cutoff is the hardest of the three.
Because Medicare uses your 2026 income to set Part B and Part D premiums for 2028, a Roth conversion made this year could affect those costs.
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