Year-End Tax Planning 2026: The Complete Checklist
October through December is when the tax year is still yours to shape. Some moves have a hard December 31 deadline; others can wait until April 15, 2027 and still count for 2026. Here is the complete checklist, split by deadline so you spend your December on the items that actually expire.
Must happen by December 31, 2026
Max out your 401(k) through payroll. Unlike an IRA, a 401(k) can only be funded from 2026 paychecks — there is no grace period. The 2026 limit is $24,500, rising to $32,500 at 50+ and $35,750 for ages 60–63. If you are behind, bump your deferral percentage now; front-loading too early in the year can forfeit the employer match in later months, so aim for an even spread.
Convert to a Roth IRA if your income is low this year. Conversions are taxable in the year you make them, so a low-income year — a sabbatical, a gap between jobs, early retirement — is the time. The deadline is December 31: convert now and the tax lands on the 2026 return. Wait until January and it belongs to 2027.
Harvest capital losses. Sell losing investments by December 31 to offset realized gains, then up to $3,000 of ordinary income. The strategy pairs with harvesting gains inside the 0% capital gains bracket: with 2026 taxable income under $49,450 (single) or $98,900 (joint), long-term gains are tax-free — a chance to reset cost basis. Watch the wash-sale rule: you cannot buy the same security within 30 days and keep the loss.
Give before midnight on December 31. Charitable cash gifts must be made by year-end to count on the 2026 return (and to qualify for the up-to-60%-of-AGI deduction). If you are 70½ or older, a qualified charitable distribution (QCD) from your IRA satisfies your required minimum distribution tax-free — up to $100,000+ in 2026 — and counts toward the gift. Annual gift-tax exclusion gifts of up to $19,000 per recipient ($38,000 per couple splitting) also reset on January 1.
By January 15, 2027: the Q4 estimated payment
Self-employed? Your fourth-quarter estimated payment is due January 15, 2027 — not December 31, but early January is still the moment to size it. Paying 100% of last year’s tax (110% above $150,000 AGI) avoids the underpayment penalty even if this year’s income jumped.
Can wait until April 15, 2027 — but do not forget
Traditional IRA: contribute up to $7,500 ($8,600 at 50+) any time before April 15, 2027 and it counts for 2026. HSA: the $4,400 self-only / $8,750 family limits (plus $1,000 catch-up at 55+) also fund until the filing deadline. Solo 401(k) employer side: the profit-sharing contribution can be made after year-end, unlike the employee deferral. These are the “grace period” accounts — use them deliberately instead of discovering them at the filing deadline.
Also worth checking in December
Review your W-4: if you owed or got a huge refund last spring, a two-minute change now fixes 2027 before it starts. Compare itemizing against the $16,100 / $32,200 standard deduction with your actual numbers — under the 2026 law the state and local tax (SALT) cap was raised, which pushes more taxpayers over the line. And if your income changed mid-year, run your full-year picture now instead of in April, when nothing can be changed.
Run the numbers
See your remaining 401(k) room with the 401(k) catch-up calculator, the tax cost of a conversion with the Roth conversion calculator, and the value of harvested losses with the capital loss carryover calculator. Size the HSA benefit with the HSA tax savings calculator, check your IRA limit with the IRA limit calculator, and fix withholding with the withholding calculator. Self-employed? Size the Q4 payment with the estimated quarterly tax calculator. Brackets, standard deduction, and the 0% gains threshold are all in our 2026 tax brackets guide, and every deduction that still counts is in the 2026 deductions list. Starting school instead? Our back-to-school budgeting guide covers the FAFSA and loan limits.