A backdoor Roth contribution is only tax-free on the contribution itself if it’s the only money in any traditional, SEP, or SIMPLE IRA. Other pre-tax IRA balances trigger the pro-rata rule.
How it works
The IRS treats every dollar across all your traditional, SEP, and SIMPLE IRAs as one combined pool for conversion purposes. The tax-free share of any conversion equals your nondeductible contribution divided by the total pool — you cannot cherry-pick just the nondeductible dollars out on their own.
What this does not include
This calculator computes the pro-rata split for a single year’s conversion; it doesn’t track basis carried forward across multiple years, which Form 8606 is specifically designed to do and which anyone doing this regularly should file correctly.
How to use this calculator
- Enter this year’s nondeductible traditional IRA contribution.
- Enter the year-end balance of any other pre-tax traditional, SEP, or SIMPLE IRA money you hold.
Frequently asked questions
Is there an income limit on doing a backdoor Roth?
No income limit applies to the conversion step itself, per the IRS source — only direct Roth contributions are income-limited, which is the entire reason this two-step strategy exists.
What triggers the pro-rata rule?
Having any other pre-tax IRA money — including an old 401(k) rolled into a traditional IRA — at the time of conversion. It doesn’t matter which account the nondeductible contribution technically sits in.
How do I avoid the pro-rata rule?
Some people roll existing pre-tax IRA balances into an employer 401(k) first (if the plan accepts incoming rollovers), leaving no other pre-tax IRA money behind before converting — a strategy this calculator can’t evaluate but can show the cost of not doing.
