How this number is made
A backdoor Roth is a non-deductible traditional contribution followed by a conversion. The pro-rata rule taxes the conversion based on the pre-tax share of all traditional IRAs, not just the account you convert. This page applies that ratio to the amount you convert. It does not know about a 401(k), which is usually outside the rule, and it is not tax advice.
- Pre-tax balance includes earnings and deductible contributions in every traditional, SEP, and SIMPLE IRA.
- Basis is the after-tax money you have already tracked. The conversion cannot exceed the total of the two.
Formula
Taxable = conversion × pre-tax balance ÷ (pre-tax balance + basis).
Worked example
With the figures already in the form, taxable part of the conversion is $5,957.
Questions
What if I have no other IRA?
Then the pre-tax box is just the earnings on the contribution, often small if you convert quickly. Type those earnings, not zero, if they exist.
Does a 401(k) count?
Usually the pro-rata pool is IRAs, not the current employer’s plan. This page only uses the numbers you type.