Backdoor Roth Pro-Rata Calculator
How much of a Roth conversion is taxable when other pre-tax IRAs exist? Every piece below can be linked to, so it opens in a window on your reader's screen, current as of the record. No form to fill in.
2026 law · Reviewed September 5, 2026 · The full page, with methodology and sources · the terms · All tools
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The conversion, the basis, and every other pre-tax IRA balance in; the taxable share, the tax at a chosen rate, and the basis carried forward out. In a frame it carries no cookies, no tracking, and a visible link back to the methodology. Your site has to allow frames; most do. The link that opens it in a small window is on the professionals page.
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- In plain words.
- A backdoor Roth is a way for higher earners to fund a Roth IRA: put after-tax money into a traditional IRA, then convert it. The catch is that the IRS treats all your traditional IRAs as one pot. If the pot also holds pre-tax money, the conversion is taxed in proportion to it, and you cannot choose to convert only the after-tax part. This tool does that proportion the way the tax form does.
- Why it matters.
- People do a backdoor Roth expecting no tax and get a surprise bill. Checking the pot first, and emptying it into a 401(k) if possible, is what makes the move clean.
- An example.
- You convert $7,500 of after-tax money, but you also have $92,500 in an old pre-tax IRA. Only 7.5 percent of the pot is after-tax, so about $6,900 of the $7,500 conversion is taxable.
- Where it stops.
- It assumes one conversion and no other IRA withdrawals that year. Rolling the pre-tax money into a 401(k) before December 31 changes the answer completely, and a spouse's IRAs are a separate pot.
The facts
Six quotable sentences on the pro-rata rule, 2026 figures.
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- A direct Roth IRA contribution phases out between $153,000 and $168,000 of income single and $242,000 to $252,000 joint for 2026. A conversion has had no income limit since 2010, which is why the backdoor exists: a nondeductible contribution, then a conversion.
- The 2026 IRA limit is $7,500, plus $1,100 from age 50. A nondeductible contribution creates basis, reported on Form 8606, that comes out tax-free.
- The pro-rata rule (§ 408(d)(2)) treats every traditional, SEP, and SIMPLE IRA a person owns as one pool. A conversion carries out basis and pre-tax dollars in the pool's proportion, measured at December 31 with the year's conversions added back; the converter cannot choose to move only the basis.
- Example: a $7,500 nondeductible contribution converted the same year, with $92,500 in other pre-tax IRAs, is 7.5% basis and 92.5% taxable: $6,938 of income on a $7,500 conversion, and $6,938 of basis stranded in the pool.
- Employer plans are not in the pool. Rolling pre-tax IRA money INTO a 401(k) that accepts it empties the pool and makes the next conversion clean; a spouse's IRAs are a separate pool.
- Nothing here turns on the calendar month: a contribution for a year can be made until the following April, but the pool is measured at the December 31 of the year of the conversion.
The same conversion, four pools
How the taxable share of one conversion rises with the rest of the pool.
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| Other pre-tax IRAs at year end | Basis share of the pool | Taxable part of the conversion | Basis left behind |
|---|---|---|---|
| $0 | 100.0% | $0 | $0 |
| $25,000 | 23.1% | $5,769 | $5,769 |
| $92,500 | 7.5% | $6,938 | $6,938 |
| $250,000 | 2.9% | $7,282 | $7,282 |
Cite and link.
The clean address, a citation generated from the record so it can never carry a stale review date, and an address for every section so you can point a reader at the exact table or method.
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- Link
- https://consideratecapital.com/tools/backdoor-roth-pro-rata
- Citation
- Considerate Capital, "Backdoor Roth Pro-Rata Calculator," reviewed September 5, 2026, https://consideratecapital.com/tools/backdoor-roth-pro-rata.
Link to a section
- The calculator https://consideratecapital.com/tools/backdoor-roth-pro-rata#calculator
- The facts https://consideratecapital.com/tools/backdoor-roth-pro-rata#facts
- Four pools https://consideratecapital.com/tools/backdoor-roth-pro-rata#key-numbers
- How the pro-rata rule works https://consideratecapital.com/tools/backdoor-roth-pro-rata#how-it-works
- Methodology https://consideratecapital.com/tools/backdoor-roth-pro-rata#methodology
- Sources https://consideratecapital.com/tools/backdoor-roth-pro-rata#sources
- Revision history https://consideratecapital.com/tools/backdoor-roth-pro-rata#revision-history
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