If you’re weighing a Roth conversion this year, the first thing to get straight is the calendar, because it’s the part people get wrong most often. A Roth conversion for 2026 has to be done by December 31, 2026 — not by the April filing deadline. That single fact changes how much runway you actually have, and it’s why “how much should I convert to a Roth before year-end” is a Q4 question, not a tax-season one.
I’m a retired chartered accountant, and conversion timing was one of the calls I got asked about most — usually in November, usually with more urgency than needed and less planning than helpful. So let me walk through the framework I found most useful: fill your bracket to the top, not past it. I’ll show the exact number for a worked example using the official 2026 brackets, and flag the traps — the deadline, the “pay the tax from outside” rule, and the fact that once you convert, you can’t take it back.
One thing up front: I’m a finance writer, not your CPA or financial advisor, and this is general information, not personalized tax advice. KnowWiser doesn’t earn a commission on anything below. The figures come from the IRS’s own releases, and I’ve dated the page so you can see how current it is.
When is the deadline to convert to a Roth for 2026?
December 31, 2026. A conversion is taxed in the calendar year the money leaves your traditional IRA, and there is no grace period into the following spring.
This is the distinction that trips people up: an IRA contribution can be made up to the April filing deadline and still count for the prior year. A conversion cannot. The two are separate transactions with separate deadlines. Money that moves from a traditional IRA to a Roth on December 30, 2026 is 2026 income; the same move on January 2, 2027 is 2027 income. That’s it — the year the funds settle is the year you’re taxed.
Two practical notes. First, your custodian’s operational cutoff is earlier than the statutory date — often the first or second week of December — because the transfer has to fully settle by the 31st. If you’re thinking about a year-end conversion, call whoever holds the account in early December, not on the 30th. Second, the tax bill lands with your 2026 return, and depending on your situation you may owe estimated tax during the year rather than all at once next April; that’s a question for your own tax preparer.
How much should you convert to a Roth before year-end?
A clean framework: convert just enough to fill your current tax bracket to its top edge, and stop before you spill into the next one. The logic is simple — a conversion stacks on top of your other taxable income and is taxed slice by slice, so the last dollars of a too-large conversion get taxed at a higher rate than the first.
Here are the 2026 federal brackets you’re filling, from the IRS’s tax-year 2026 inflation release (Rev. Proc. 2025-32):
| Rate | Single (taxable income over) | Married filing jointly (over) |
|---|---|---|
| 10% | $0 | $0 |
| 12% | $12,400 | $24,800 |
| 22% | $50,400 | $100,800 |
| 24% | $105,700 | $211,400 |
| 32% | $201,775 | $403,550 |
“Taxable income” here means income after your standard or itemized deduction — for 2026 the standard deduction is $16,100 for single filers and $32,200 for married filing jointly (IRS, same release). If you’re not sure what your taxable income is before the conversion, our take-home pay calculator will get you the number and your starting bracket.
Worked example: filling the 22% bracket as a single filer
Take a single filer — this is arithmetic, not a real client — with $60,000 of taxable income for 2026, before any conversion. Where’s the top of their bracket?
The 22% bracket for a single filer runs up to $105,700. They’re sitting at $60,000, so they have $105,700 − $60,000 = $45,700 of room before the next dollar gets taxed at 24%.
- Convert $45,700. The whole conversion is taxed at 22%, a federal tax of about $10,054. Their taxable income lands right at the top of the 22% bracket, $105,700. Not a dollar into 24%.
- Convert $45,701. That last dollar is taxed at 24%. It’s not a disaster — only the dollars above $105,700 pay the higher rate — but it’s the line the “fill to the top” rule is watching.
- Convert $100,000. Now $45,700 fills the rest of the 22% bracket ($10,054) and the remaining $54,300 is taxed at 24% ($13,032), for about $23,086 total — an effective rate of 23.1% on the conversion. Still fine if you expect a higher rate in retirement, but you’ve deliberately paid 24% on part of it.
The point isn’t that spilling into 24% is forbidden. It’s that the decision should be on purpose. If you’ve got a low-income year — a gap between jobs, early retirement before Social Security starts, a business loss — filling the 10% and 12% brackets you’d otherwise waste is often the single best conversion opportunity you’ll get. The bracket edges tell you where to stop.
If you’re married filing jointly, the same move uses the MFJ row: the 22% bracket runs to $211,400 and the 24% bracket to $403,550, so a couple has far more room before each jump.
Should you pay the conversion tax from the IRA or from savings?
From savings, whenever you can. Paying the tax with outside cash means every dollar you converted stays inside the Roth, compounding tax-free for as long as you leave it there.
The alternative — withholding the tax out of the conversion itself — quietly does two bad things. First, fewer dollars actually reach the Roth, so you’ve shrunk the tax-free account you were trying to build. Second, if you’re under 59½, the IRS treats the withheld portion as an early distribution to which the 10% additional tax generally applies (Tax Topic 557). So you can end up paying a penalty on the money you used to pay the tax. Set the cash aside before you convert, and the whole point of the conversion — a bigger tax-free balance — stays intact.
Want to see the after-tax difference over your own time horizon, with the tax paid either way? That’s exactly what the calculator I link at the end does.
Can you undo a Roth conversion if you convert too much?
No. The IRS states that a conversion made on or after January 1, 2018 cannot be recharacterized — the Tax Cuts and Jobs Act removed the ability to reverse one.
This matters for how you approach the whole thing. Before 2018, if you converted and then decided it was a mistake, you had until the following October to unwind it. That escape hatch is closed. A 2026 conversion is permanent the day it settles. Which is the real argument for the “fill the bracket” discipline and for converting in slices across several years rather than one big irreversible move: you can always convert more next year, but you can’t take back a conversion you regret.
What are the Roth conversion 5-year rules?
There are two, both spelled out in IRS Publication 590-B, and they run on separate clocks.
- The earnings clock. For your earnings to come out tax-free, it generally has to be at least five tax years since your first Roth contribution, and you have to be 59½ or meet another qualifying condition.
- The per-conversion clock. Each conversion has its own five-year period. Withdraw the converted amount within five years and, if you’re under 59½, the 10% additional tax can apply.
If you’re converting with the intent to leave the money invested for years — which is the usual reason to convert at all — both clocks typically look after themselves. The details and exceptions are in Publication 590-B; it’s worth a skim before a large conversion.
A couple of caveats worth naming
Extra income from a conversion doesn’t live in a vacuum. Two knock-on effects show up often enough to flag, though the specifics depend on your situation and I’m not going to put numbers on them here:
- Medicare (IRMAA). For people on Medicare, higher modified adjusted gross income can raise Part B and Part D premiums through the income-related monthly adjustment amount, which uses your income from two years earlier. A big conversion at 63 or 64 can nudge premiums up later.
- ACA subsidies. If you buy health coverage through the marketplace, a conversion raises the income that premium tax credits are calculated against, which can shrink a subsidy for that year.
Neither is a reason to skip a conversion — they’re reasons to check whether one of these thresholds is close before you pick your number. That’s a conversation for your tax preparer or a benefits counselor, with your actual figures.
The short version
The deadline is December 31, 2026, and it’s firm — a conversion is a calendar-year event, not a tax-season one. The framework is to fill your current bracket to its top edge and stop, converting more next year rather than spilling into a higher rate on purpose. Pay the tax from outside savings so the whole balance keeps growing tax-free. And remember it’s permanent, so pick the number deliberately.
If you’re still getting your arms around traditional-versus-Roth in general, I’d start with our 401(k) vs Roth IRA guide — and if you’re near the age where forced withdrawals begin, a large traditional balance you’ll eventually be required to draw down is often the strongest case for converting early, while you still control the timing.
Run your own bracket-fill number
The one number this whole article is about — how much you can convert before you spill into the next bracket — is worth calculating for your real income, not a worked example. Our Roth conversion calculator does exactly that: enter your other taxable income and an amount to convert, and it shows the federal tax bracket by bracket using the 2026 IRS tables, which brackets the conversion fills, the after-tax value of converting versus not over your time horizon, and the break-even withdrawal rate — with the tax paid either from savings or from the conversion. Start with a number that fills your bracket to the top, then adjust from there.
Sources
- IRS — Tax inflation adjustments for tax year 2026 (2026 federal brackets and standard deduction; Rev. Proc. 2025-32)
- IRS — Retirement plans FAQs regarding IRAs (a conversion made on or after January 1, 2018 cannot be recharacterized)
- IRS — Publication 590-B (Roth 5-year rules; conversion and early-distribution rules)
- IRS — Tax Topic 557 (10% additional tax on early distributions)
Verified as of 2026-09-26 against irs.gov: the 2026 federal brackets and standard deduction (Rev. Proc. 2025-32), the December 31 calendar-year conversion deadline (versus the April deadline for IRA contributions), that conversions on or after January 1, 2018 cannot be recharacterized, and the Roth 5-year rules in Publication 590-B. IRMAA and ACA effects are noted as caveats, not quantified. Tax rules change and every situation differs; confirm your own numbers on irs.gov or with a tax professional before you act.