Year-end tax moves for 2026: what each one does to your federal tax, state tax, 2028 IRMAA and ACA credit
Enter what 2026 looks like so far. Seven year-end moves are run through the open federal and state tax engine, one at a time and together, and each shows the change in four numbers, 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.
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.
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.
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. The 2028 tiers are not published yet; the tool uses the 2026 tiers, so a warning can come early but not late.
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.
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.