Year-end tax planning for 2026: what a Roth conversion, tax-loss harvesting, a QCD or your last RMD does to your tax before December 31
Before December 31, 2026, seven moves can still change your 2026 tax: a Roth conversion, harvesting capital losses, harvesting long-term gains in the 0% band, bunching several years of giving into 2026, a QCD instead of a cash gift, taking the rest of your RMD, and extra December withholding or a fourth-quarter estimate (due January 15, 2027). Each one can move four numbers: your federal tax, your state tax, the Medicare (IRMAA) premium your 2026 income sets for 2028, and an ACA premium credit if you have marketplace coverage. The tool below figures all four for your numbers; your 2026 baseline and one move in full are free.
Enter what 2026 looks like so far. The open federal and state tax engine runs each move one at a time and together, with the cliffs it crosses and its deadline.
An estimate from QuantCalc's open tax engine for the 2026 tax year. Not tax advice.
Your 2026 so far
Only filing status, age and state are needed. Each group says what it adds. Amounts are for the whole of 2026: what has happened plus what you expect.
HouseholdFiling status, ages, state, Medicare and ACA coverage.
2026 incomeAdd income to see the brackets, Social Security taxation and every move.
Married filing jointly: several states tax a couple by each spouse’s own income (Arkansas, Delaware, Maryland, Minnesota, Missouri, North Dakota, Ohio and Virginia, and every retirement exclusion capped per spouse), so the state tax depends on whose income it is. Evenly is the default: the engine’s neutral split and the one our published examples use. With “evenly” or one name, what a move adds or removes follows the same split; with your spouse’s own amounts, it is yours. Federal tax does not depend on it.
AccountsAdd your IRA balance to see the RMD, QCD and conversion moves; unrealised gains and losses for the harvesting moves.
Deductions and givingAdd your planned giving (and 2027–2028's) to see bunching and the QCD.
Payments and planningAdd your 2025 tax to see the underpayment penalty and the Q4 move.
The seven moves
What can you still do before December 31, 2026 to change your 2026 tax?
Seven moves: a Roth conversion, harvesting losses, harvesting long-term gains in the 0% band, bunching several years of giving into 2026, giving through a QCD instead of cash, taking the rest of your RMD, and a fourth-quarter estimate or extra December withholding. Six must be finished by December 31, 2026; the fourth-quarter estimate is due January 15, 2027, and a first RMD can wait until April 1, 2027.
Which move is worth most depends on the household: see the seven moves priced for 12 retiree households and the same QCD and conversion in each of the 51 jurisdictions. For one decision in depth, the charitable deduction calculator compares itemizing, bunching and a donor-advised fund, and the 2026 estimated tax calculator shows what to pay by January 15.
Does a Roth conversion in December lower your 2026 tax?
No. The converted amount is ordinary income for 2026, so 2026 tax goes up, and the conversion can also raise the Medicare premiums 2026 income sets for 2028 and lower an ACA credit. It is tax paid now at a known rate instead of later. The tool shows its 2026 cost and the marginal rate on the next $1,000, to compare with the rate you expect later.
What is the deadline for a Roth conversion for 2026?
December 31, 2026. A conversion counts in the year the money leaves the traditional IRA, and unlike an IRA contribution it cannot be made for 2026 after the year ends (IRS Pub. 590-A). If you also owe an RMD this year, take it first: the RMD itself cannot be converted. Allow for your custodian’s processing time in the last week of December.
How does 2026 income affect your Medicare premiums?
IRMAA uses modified AGI from two years earlier, so 2026 MAGI sets 2028 Part B and Part D premiums. Each tier is a cliff: a dollar over a tier floor raises the surcharge for the whole year. CMS has not published the 2028 tiers yet: the tool counts the surcharge on projected 2028 tiers (the 2026 ones indexed at 2% a year, the table the IRMAA projector uses) and states the 2026 floor, the latest published, beside it as the cautious line, because the 2028 floor may come in below the projection.
Is there an ACA subsidy cliff in 2026?
Yes. From 2026 the premium tax credit ends again above 400% of the federal poverty line, and there is no cap on paying back advance credit. A move that pushes ACA income over the line can cost the year's whole credit; the tool warns before it does.
Is harvesting gains at the 0% rate free?
Not always. The gain can make more Social Security taxable, shrink the senior deduction, cross an IRMAA tier or the ACA line, and raise state tax. The tool shows the change in your whole 2026 total.
After the moves: the whole 2026 return
The 2026 Return Preview shows every Form 1040 line and schedule the engine fills for your numbers, your state’s tax and the refund or amount owed against what you have paid. It comes with the same pass; the refund or amount owed alone is free in the 2026 tax return calculator.
What is in the tool, and what is not
Not modelled
Your numbers are computed in this browser tab and are not sent to QuantCalc. The paid PDF sends the final scenario once to QuantCalc's tax engine to confirm every figure. Sources for every federal rule: federal calculation order; state rules: state tax engine docs.