Backdoor Roth IRA Calculator (Pro-Rata Rule)
Enter your existing Traditional IRA balance, nondeductible contributions, and conversion amount to estimate the taxable portion of a Backdoor Roth IRA conversion under the IRS pro-rata rule.
What Is a Backdoor Roth IRA?
A Backdoor Roth IRA is a strategy used by high earners who are blocked from contributing directly to a Roth IRA by income limits (MAGI phase-out). They first make a nondeductible (after-tax) contribution to a Traditional IRA, which has no income limit, then convert that money to a Roth IRA. Since conversions themselves are not subject to income limits, this effectively works around the usual Roth contribution restrictions — hence the "backdoor" nickname.
However, this strategy has an easily overlooked pitfall. The taxable portion of the conversion is not based solely on this year's nondeductible contribution — it is determined by the "pro-rata rule" (IRC §408(d)(2)), which aggregates all of your Traditional/SEP/SIMPLE IRA balances together. If you have pre-tax IRA money from an old 401(k) rollover, part of your conversion will be taxable, often resulting in a larger tax bill than expected.
How to Use
- Enter your basis carried over from prior years Enter the cumulative nondeductible contribution basis from your prior Form 8606 filings. Leave at 0 if this is your first time
- Enter this year's nondeductible contribution Enter the after-tax contribution you made to a Traditional IRA this year
- Enter your year-end pre-tax IRA balance Enter the total year-end balance across all your Traditional/SEP/SIMPLE IRA accounts, excluding this year's conversion
- Enter this year's conversion amount Enter the amount converted from a Traditional IRA to a Roth IRA this year, and the taxable amount is calculated automatically
Tips for getting more out of it
- You can convert across different years, but the pro-rata calculation always uses the year-end balance for the year in which the conversion took place.
- If you hold multiple Traditional/SEP/SIMPLE IRA accounts, the pro-rata calculation always aggregates all of them together rather than treating each separately.
- Conversions may be subject to state income tax in addition to federal tax. This tool only estimates the federal pro-rata ratio.
- This tool provides a simplified estimate. For an accurate tax determination, consult a tax professional or the latest IRS Form 8606 instructions.
Use Cases
High earners evaluating Roth IRA contribution options
Estimate the tax cost of this alternative strategy before contributing, when income limits block direct Roth IRA contributions
Understanding the tax impact of an old rollover IRA
If you rolled over an old 401(k) into a Traditional IRA, check how that balance affects the tax cost of a backdoor Roth conversion
Considering an IRA-to-401(k) rollover strategy first
Use this to evaluate whether rolling pre-tax IRA balances into your current employer's 401(k) (money.wealth.401k_calculator) could reduce the pro-rata rule impact
Glossary
- Backdoor Roth IRA
- A strategy in which someone blocked from contributing directly to a Roth IRA by income limits instead makes a nondeductible Traditional IRA contribution and converts it to a Roth IRA.
- Pro-Rata Rule
- An IRS rule (IRC §408(d)(2)) that determines the taxable portion of a Roth conversion based on the ratio of nondeductible basis to the total balance across all of your Traditional/SEP/SIMPLE IRAs.
- Nondeductible Contribution
- A Traditional IRA contribution for which you cannot claim a tax deduction, typically due to income limits. It is reported to the IRS on Form 8606 and tracked as basis.
- Form 8606
- The IRS form used to report nondeductible contributions, conversions, and pro-rata calculations. Basis carries forward across multiple years, so it must be filed accurately every year.
- Basis
- The cumulative amount of after-tax (nondeductible) contributions you have made, which becomes the portion of future withdrawals or conversions treated as nontaxable.
- Aggregation Rule
- For pro-rata rule purposes, all of your Traditional/SEP/SIMPLE IRA accounts are treated as one combined account rather than calculated separately.
Frequently Asked Questions
Side Note — A Legal Loophole Called the "Back Door"
The name "Backdoor Roth IRA" is not an official tax term. It emerged around 2010, when Congress removed the income limit on Roth conversions (previously restricted to those earning under $100,000 a year). Financial planners and bloggers coined the term to describe a workaround that let high earners route money into a Roth IRA despite the usual contribution limits. The IRS itself never uses the phrase, but it has become standard among tax professionals.
What makes this strategy interesting is that it is not a gray area — the IRS's own guidance and Form 8606 instructions explicitly acknowledge it as fully legal. In fact, the 2017 Tax Cuts and Jobs Act's congressional committee reports note that lawmakers deliberately chose not to prohibit backdoor Roth conversions. That said, Congress has considered bills to restrict the strategy on several occasions, so future rule changes remain possible.
Japan has little equivalent concept of income-based contribution restrictions (iDeCo's limits are based on employment category rather than income), so this kind of "workaround" rarely becomes necessary there. The contrast is a striking one: the U.S. tax system restricts high-income benefits for redistributive reasons, yet a legal loophole remains built into the design.