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Backdoor Roth Pro-Rata

Convert $7,000 with $94k of pre-tax IRA money and $6,580 is taxable. Run your numbers.

The backdoor Roth fails silently for anyone with an old rollover IRA: the pro-rata rule aggregates ALL your traditional, SEP, and SIMPLE IRAs and taxes any conversion by the pre-tax share of the whole pot. Most explainers bury this in the third paragraph. This calculator puts it first — your exact taxable amount, the tax bill at your bracket, your remaining basis, and the 401(k) roll-in rescue that makes the conversion clean.

Why people use this

High earners attempting a backdoor Roth with an old rollover IRA use it before December 31: the pro-rata rule taxes the conversion by the pre-tax share of ALL their IRAs, and the tool shows the bill — plus the 401(k) roll-in rescue that makes it clean.

How it works

1. Enter the pre-tax balance across ALL your traditional/SEP/SIMPLE IRAs (they aggregate).
2. Enter your after-tax basis — total non-deductible contributions, from your Form 8606 history.
3. Enter the amount you plan to convert and your marginal tax rate.
4. Read the taxable split, the bill, and what changes if you roll the pre-tax money into a 401(k) first.

Common questions

How does the pro-rata rule tax my backdoor Roth conversion?

Form 8606 math: your conversion is tax-free only in proportion to your after-tax basis over the TOTAL value of all your traditional, SEP, and SIMPLE IRAs. With $94,000 pre-tax and $6,000 of basis, converting $7,000 is 6% tax-free — $420 — and $6,580 is taxable ordinary income. Converting less does not dodge it; the percentage follows every dollar. The only clean conversions are ones where pre-tax IRA money is zero on December 31.

Does my 401(k) count in the pro-rata calculation?

No — 401(k), 403(b), and TSP balances are excluded; only IRAs aggregate. That exclusion is the rescue: if your current employer's 401(k) accepts roll-ins, move your pre-tax IRA money there before December 31, leaving only after-tax basis in the IRA. The conversion then goes through nearly 100% tax-free. Check the plan's roll-in policy and fund menu first — not every plan accepts them.

What paperwork does a backdoor Roth require?

Form 8606, twice over: once to report the non-deductible traditional IRA contribution (which establishes your basis) and again to report the conversion and its pro-rata split. Each spouse files their own 8606. The penalty for failing to file is $50 per occurrence, but the real cost is worse: without the 8606 paper trail, the IRS treats your basis as zero and your "tax-free" conversion becomes fully taxable years later. Custodians do not track basis for you — the 8606 history is your only proof.

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