Updated August 1, 2026. Quick answer: the amount you can convert without crossing into the next tax bracket is not a number you should have to guess or type in — it is the top of your current bracket minus your taxable income, and both figures are published. This works it out from the 2026 federal tables in IRS Rev. Proc. 2025-32 for all four filing statuses, then prices every rung above it too, because filling one bracket is rarely the only sensible answer. A single filer with $90,000 of income has $31,800 of room in the 22% bracket, at a federal cost of $6,996.
The calculator
Why the answer is a ladder, not a single number
“Convert to the top of your bracket” is the standard advice, and it is often wrong by accident: it treats the bracket you happen to be in this year as if it were meaningful. It is not. What matters is the rate you pay now against the rate the same dollars would face later — in an RMD year, or in a surviving spouse’s single brackets, or in an heir’s. If your later rate is higher, stopping at the top of a low bracket leaves cheap room unused.
That is why the table above prices every rung rather than just the first one. The effective-rate column is the one to read: it blends the rates you cross, so converting into the 24% bracket does not cost 24% on the whole amount. It is almost always lower than people assume, and that gap is where the decision actually gets made.
One structural point that catches surviving spouses in particular: single brackets are exactly half the joint brackets, until they are not. The doubling holds up through the 32% band and then breaks, which is why a widow or widower can land in a higher rate on the same income.
What this does not include, and where each one lives
Bracket room is federal ordinary-income tax and nothing else. Four other things can be triggered by the same conversion, and any of them can cost more than the bracket you were protecting:
- Medicare premiums, two years later. A 2026 conversion sets 2028 IRMAA, and the tiers are cliffs rather than phase-ins — the lag and the cliffs.
- Your long-term capital gains. Conversion income stacks underneath them and can push gains from 0% into 15% — how the stacking works.
- The 3.8% surtax. Conversion income is not itself subject to NIIT but it raises the MAGI that exposes your other income to it — the wrinkle most sources state backwards.
- State tax, and ACA subsidies if you are pre-65. What your state does with conversion income, and what it does to a marketplace subsidy.
The 2026 tables this uses
Top of each bracket, taxable income, all four filing statuses. Married filing separately is included because it is exactly half the joint figures at every threshold and is routinely omitted from calculators for that reason — which does not help you if it is your filing status.
| Rate | Single top | Married filing jointly top | Head of household top | Married filing separately top |
|---|---|---|---|---|
| 10% | $12,400 | $24,800 | $17,700 | $12,400 |
| 12% | $50,400 | $100,800 | $67,450 | $50,400 |
| 22% | $105,700 | $211,400 | $105,700 | $105,700 |
| 24% | $201,775 | $403,550 | $201,750 | $201,775 |
| 32% | $256,225 | $512,450 | $256,200 | $256,225 |
| 35% | $640,600 | $768,700 | $640,600 | $384,350 |
| 37% | no ceiling | no ceiling | no ceiling | no ceiling |
| Standard deduction | $16,100 | $32,200 | $24,150 | $16,100 |
Add $1,650 per person to the standard deduction if married and 65 or older or blind, or $2,050 if unmarried. The calculator applies this for you. Any other deduction you claim — itemising, or a deduction you qualify for beyond the standard amount — goes in the last input, and raises your bracket room dollar for dollar.
Once you know the amount
Three things decide whether the conversion is worth doing at all, and this page answers none of them: whether it pays in your situation, where the tax money comes from (paying it out of the IRA itself changes the maths badly), and when the tax is actually due, which is a quarterly question and a common surprise.
Two neighbouring tools, if this one is not the shape you need: the guardrail estimator if you already know the cap you want to stay under and want to test one amount against it including an IRMAA cap, and the full cost of a conversion for the state and Medicare layers on top of the federal number. If you are converting across several years, sequence it with the withdrawal order that funds it.
2026 rate schedules and standard deductions from IRS Rev. Proc. 2025-32, read from irs.gov and independently re-verified on August 1, 2026 by recomputing every bracket chain against the published base-tax column. Thresholds are indexed and change every year — check the current year before relying on a figure. General information, not tax advice.
Nobody withholds for you in retirement. Work out your safe-harbour number — 90% of this year or 100% of last year, whichever is lower — and if the year is already off track, withholding from a December RMD counts as paid evenly across all four quarters, which an estimated payment does not.
Thinking about clearing the mortgage first? Run it against your own numbers — including the deduction reality check, since a couple both over 65 has a $35,500 standard deduction in 2026 and most mortgage interest therefore deducts nothing, and the gross-up if the money comes from an IRA.
The pro-rata rule is not fixed — the denominator is. The fraction is measured on 31 December, so moving pre-tax IRA balances into an employer 401(k) before then removes them from it entirely, and your after-tax basis is legally barred from following. Order of operations matters, and a SIMPLE IRA inside its first two years blocks it.
All the numbers, kept current. This page uses 7 figures from our claims register — every figure we track is on one page, each with the year it applies to and a plain statement of what makes it move.