How the maths works
How to use it
- Enter the amount you are thinking of moving out of a Traditional IRA or an old 401(k).
- Enter every other dollar of income you expect this year. This matters more than it looks: a conversion stacks on top of your existing income, so the tax it costs depends entirely on what is already underneath it.
- Read Room Left in Bracket first. That is the largest conversion you can do without any of it being taxed at the next rate up — and it is the number most people should be sizing against rather than converting a whole account at once.
- Set your expected retirement tax rate honestly. If it is higher than the effective rate shown, converting wins. If it is lower, wait for a year when your income drops.
- Switch Pay the tax from to see the cost of paying it out of the conversion instead of from savings. It is worse than most people expect.
A worked example
On $70,000 of other income filing single, the 22% bracket runs out at a taxable income of $105,700 — so after the standard deduction there is roughly $51,800 of headroom. Convert $30,000 and it all sits inside 22%, costing about $6,600 at an effective rate of 22%. Convert $80,000 instead and the last chunk crosses into 24%, so the effective rate climbs and the extra tax buys you nothing you could not have had by splitting the conversion across two years. That is the entire argument for converting in slices.
Where this sits in the Financial Literacy resource
A calculator tells you where you are. It does not tell you what to do next, and a number without a plan behind it tends to produce anxiety rather than progress. These stages are free, need no account, and cover the decision this calculator is measuring.
Common questions
Is there an income limit on a Roth conversion?
No. The income limit people are thinking of applies to Roth IRA contributions, which phase out between $153,000 and $168,000 for single filers and $242,000 and $252,000 for married filing jointly in 2026. There has been no income limit on converting since 2010, when the old $100,000 cap was removed and never reinstated. That gap is what makes the backdoor Roth possible.
How much tax will I pay on a Roth conversion?
The converted amount is taxed as ordinary income in the year you convert, stacked on top of your other income. That means the cost is marginal, not average — it depends on which brackets the conversion fills, which is what this calculator works out. Converting an amount that fits inside your current bracket costs that bracket rate; converting more pushes the excess into the next rate up.
Should I pay the conversion tax from the converted money?
Almost never. Paying from the conversion shrinks the balance you were trying to grow tax-free, and if you are under 59½ the withheld amount is treated as an early withdrawal and gets hit with the 10% penalty on top. If you cannot pay the tax from savings outside the account, that is usually a signal to convert a smaller amount rather than to pay it from inside.
When is the best time to do a Roth conversion?
In a year when your income is unusually low, because the tax is charged at your rate that year. Common windows are a gap between jobs, a year of study or caregiving, a business loss year, and above all the years between retiring and the start of Social Security or required minimum distributions — when many people have several consecutive low-income years and a large pre-tax balance sitting there.
Can I undo a Roth conversion if it turns out badly?
No. Recharacterisation of conversions was eliminated in 2018. Once you convert, the tax is owed for that year and the decision is permanent, which is why sizing it correctly before you execute matters more than it used to.
What this calculator is not
It is an educational model, not a projection and certainly not advice. It knows nothing about your income, your state, your debts or your benefits status, and it ignores taxes and fees unless the page says otherwise. If you receive SSI or SSDI some of this maths works differently and getting it wrong can cost you eligibility — start with the Disability Wealth Guide instead. Our sourcing and correction policy is on the editorial standards page.
Nothing here is stored. Every calculation runs in your browser. No numbers are transmitted, logged or saved to any server, and no account is required. Close the tab and it is gone.