The Backdoor Roth IRA — and the Pro-Rata Trap

Taxes By the RetiPilot Editorial Team · Jul 1, 2026 · 6 min read

If your income is too high to contribute to a Roth IRA directly, a two-step move called the backdoor Roth can get you there anyway. It works beautifully — unless an old IRA quietly triggers the pro-rata rule.

Why the back door exists

Direct Roth IRA contributions phase out above certain income levels — in recent years, modified adjusted gross income around $165,000 for single filers and $246,000 for married couples filing jointly (thresholds adjust annually). But there is no income limit on making a nondeductible contribution to a traditional IRA, and no income limit on converting a traditional IRA to a Roth.

Put those two rules together and you get the backdoor Roth: contribute to a traditional IRA without taking a deduction, then convert that money to a Roth shortly after. Done cleanly, almost nothing is taxable at conversion, because you already paid tax on the contribution and it hasn’t had time to grow.

The pro-rata trap

Here is where people get burned. When you convert, the IRS doesn’t let you choose which dollars you’re converting. All of your traditional, SEP, and SIMPLE IRAs are aggregated, and every conversion is treated as a proportional slice of pre-tax and after-tax money across all of them.

Say you make a $7,000 nondeductible contribution, but you also have a $93,000 pre-tax rollover IRA from an old job. Your IRAs are now 93% pre-tax — so 93% of your “backdoor” conversion is taxable income, exactly what you were trying to avoid. Nondeductible contributions are tracked on IRS Form 8606, and keeping that form current is what protects your after-tax basis.

The clean-up move

There is a well-worn fix. If your workplace 401(k) accepts roll-ins, you can move the pre-tax portion of your IRAs into the plan, leaving only after-tax basis behind. With the pre-tax money out of the way, the aggregation math changes completely — the remaining IRA is all basis, and converting it triggers little or no tax. Vanguard’s research on Roth conversions notes that separating basis this way can drive the break-even tax rate on a conversion all the way to zero.

Why it can also strengthen the case for converting

One subtle finding from that same research: if you plan to make backdoor Roth contributions in future years, doing a conversion now becomes more attractive than the usual current-vs-future tax-rate comparison suggests. Clearing out your traditional IRA is what opens the back door — and years of future tax-free compounding get counted on the conversion’s side of the ledger.