How much should I convert to Roth before Medicare starts?
There is no single right number. Three limits usually decide it: your tax bracket, Medicare IRMAA from age 63, and, before 65, the health insurance subsidy cliff.
Start with the limits, not a number
A Roth conversion adds the converted amount to your income for the year. Which limit matters most depends on your age and how you are insured.
| Limit | When it applies | What it looks like |
|---|---|---|
| Tax bracket | Every year | Each slice is taxed at the rate of the bracket it lands in |
| Medicare IRMAA | Income at about age 63 and later | A line at $109,000 single or $218,000 joint for 2026 |
| ACA subsidy cliff | Years you buy marketplace insurance before 65 | Credit ends above 400% of the poverty line |
| Social Security tax | Once you claim benefits | More of your benefit becomes taxable |
Before 63: usually the bracket and the subsidy
If you start Medicare at 65, income before 63 does not set Medicare premiums, so IRMAA is not a constraint yet. The bracket is. A couple filing jointly with $40,000 of taxable income has $60,800 of room before the 12% bracket ends at $100,800. Converting all of it would cost about $7,296 in federal tax. Staying in the 22% bracket, which ends at $211,400, allows up to $171,400 in total. If you are on a marketplace plan, a conversion also raises the income used for your credit, so check the subsidy calculator first.
At 63 and 64: add IRMAA
These years set your first Medicare premiums. A single filer with $90,000 of other income has $19,000 of room before the $109,000 line (using the 2026 lines as an estimate). Going over it by a dollar adds about $95.70 a month, roughly $1,148 a year, for that premium year. See why age 63 matters.
A simple order of work
- Estimate your income for the year without any conversion.
- Find the nearest limit above it that applies to you.
- Convert up to that limit, not past it, and repeat each year.
- Many people pay the conversion tax from savings outside the IRA, so more of the money keeps growing tax-free.
Find your bracket room, with a Medicare check →
Common questions
What age should I start Roth conversions?
There is no single age. Many people convert in the years between retiring and starting Social Security or required withdrawals, when income is lower. The age-63 rule only matters for the Medicare premium effect.
Does a Roth conversion raise my ACA subsidy income?
Yes. The converted amount is taxable income, so it raises the income used for your marketplace credit.
Can I undo a conversion if it pushes me over a line?
No. Conversions can no longer be reversed, so estimate the amount before you convert.
Keep reading
Sources: IRS Rev. Proc. 2025-32; CMS: 2026 Part B premiums and IRMAA; IRS: Roth IRAs