Every Money Deadline Before 31 December 2026 — and Which Ones Can Wait

31 December is the year’s hardest money deadline — but not every year-end task shares it. Some things genuinely must happen before midnight (your 401(k) contributions, a Roth conversion, FSA spend-down); others have months of grace you are probably not using. Here is every deadline that matters before the year ends, sorted by what happens if you miss it.

Must happen by 31 December 2026

• 401(k) elective deferrals: $24,500 for 2026, plus an $8,000 catch-up from age 50 (or the $11,250 “super catch-up” at ages 60–63). The real deadline is your last paycheque of the year — payroll cutoffs arrive earlier than you think, so check with HR now, not in December.
• Roth IRA conversions: must be completed within the calendar year to count for 2026.
• Realise gains and losses: tax-loss harvesting only works if the sale settles in 2026 — selling in January is a 2027 event.
• Charitable gifts: cash and securities must change hands by 31 December to count for this year’s deduction.
• FSA spend-down: health FSAs are use-it-or-lose-it — some plans offer a short grace period or a small rollover, but check yours before December rather than discovering the rule in January.
• Required minimum distributions: if you are 73 or older (75 if born in 1960 or later), your annual RMD must leave the account by 31 December. A missed RMD carries a 25% excise tax on the amount you should have taken — reducible to 10% if you correct it promptly.
• High earners: from 2026, catch-up contributions from prior-year wages above $150,000 must go into a Roth account — see our Roth catch-up rule guide.

Can wait until spring — but put them in the diary

• 2026 IRA contributions: until 15 April 2027 ($7,500; $8,600 at 50+).
• 2026 HSA contributions: until 15 April 2027 ($4,400 individual / $8,750 family, plus $1,000 catch-up from 55) — the most overlooked extension on this list.
• SEP-IRA and Solo 401(k): can still be opened and funded until your tax-filing deadline (including extensions) — the freelancer’s last-chance retirement contribution.
• Q4 estimated tax: due 15 January 2027.

Already closed for 2026 — plan for next year

SIMPLE IRA and safe-harbor 401(k) setups needed to be in place by 1 October — that door is shut for 2026. If you run a small business, diary September 2027 now.

For readers in the UK and Canada

Year-end means different things in different tax systems.