Backdoor Roth pro-rata calculator
Why a backdoor Roth is rarely tax-free, how much of it is actually taxable, and the one move that fixes it.
- Taxable portion
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- Non-taxable portion
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- Share that escapes tax
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- Pre-tax money in your IRAs
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- Tax if that were rolled into a 401(k)
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Point at any line to see what it means.
What this is actually calculating.
A backdoor Roth is a non-deductible contribution to a traditional IRA followed by a conversion. People expect it to be tax-free, because the contribution was made with money already taxed. It usually is not.
The IRS does not look at the account you contributed to. It aggregates every traditional, SEP and SIMPLE IRA you own and taxes the conversion in proportion to how much of that total is pre-tax. Contribute seven thousand alongside a ninety-three thousand pre-tax IRA and only seven percent of the conversion escapes, no matter which account the money physically left.
The parts that decide the answer.
It is a denominator problem
The taxable share is decided by your total IRA balance, not by the account you used. Shrink the pre-tax part of that total and the arithmetic changes completely.
A 401(k) is the usual fix
Pre-tax money rolled into an employer plan leaves the IRA aggregate entirely, because 401(k) balances are not counted. Do that first and the same conversion can be entirely tax-free.
Which balance to enter
Everything in your traditional, SEP and SIMPLE IRAs before this conversion leaves them, which is the figure Form 8606 arrives at by taking the December 31 balance and adding back what you converted during the year. The date still matters for planning: rolling the pre-tax money into a 401(k) in November works, in January of the following year it does not.
Not every account counts
Your traditional, SEP and SIMPLE IRAs are aggregated. Roth balances, 401(k)s, inherited IRAs and your spouse's IRAs are not.
Before you rely on it.
Does my spouse's IRA count?
No. The aggregation is per person, so a spouse's balances are irrelevant to your calculation, and each of you is measured separately.
What if I convert more than my basis?
Anything above the basis is taxable regardless. The pro-rata rule decides how the basis is spread, not whether the excess is taxed.
Can I still do this if my 401(k) will not accept a rollover?
Then the pro-rata result stands. Some plans do not accept incoming rollovers, and a solo 401(k) is sometimes the answer for an owner. That is worth confirming before contributing.
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