The pro-rata rule (IRC §408(d)(2)) aggregates all your traditional, SEP, and SIMPLE IRAs into one pool, making a proportional share of any conversion taxable if any of the pool is pre-tax. Three ways to avoid it: (1) roll all pre-tax IRA dollars into a 401(k) (excluded from the calculation); (2) convert the entire pre-tax balance and pay the tax now; or (3) wait until you have no pre-tax balance.

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Quick Facts

  • infoPro-rata rule aggregates traditional + SEP + SIMPLE IRAs per IRC §408(d)(2). Not Roth IRAs. Not 401(k)s.
  • check_circleBest fix for most readers: roll pre-tax IRA into a 401(k). Most employer 401(k) plans accept incoming rollovers from traditional IRAs. The 401(k) balance doesn't count in the pro-rata calculation.
  • infoAggregation is calculated on December 31 of the conversion year. So a clean-up rollover into a 401(k) before year-end works even if your IRA had pre-tax balance earlier in the same year.
  • warningSEP and SIMPLE IRAs ARE aggregated. If you have a self-employed SEP-IRA, that's part of the pool. Rolling SEP/SIMPLE into a 401(k) is allowed under SECURE 2.0 §602.
  • check_circleInherited IRAs are excluded. They're tracked separately and don't affect your own pro-rata calculation.

How the Pro-Rata Math Actually Works

The IRS calculates basis allocation using your December 31 balance across all your traditional, SEP, and SIMPLE IRAs combined, then determines what fraction is basis (after-tax) vs. pre-tax.

Worked example: $92,500 pre-tax in a rollover IRA + $7,500 nondeductible contribution to a separate traditional IRA = $100,000 total, of which $7,500 (7.5%) is basis. If you convert $7,500 from the nondeductible-only account to a Roth IRA on December 15:

  • Tax-free portion: $7,500 × 7.5% = $562.50
  • Taxable portion: $7,500 × 92.5% = $6,937.50

You pay ordinary income tax on $6,937.50. Worse, $6,937.50 of basis remains in the traditional IRAs (the basis "moved" with the converted dollars). Future conversions face the same proportional rule.

Path 1: Roll Pre-Tax IRA Into a 401(k)

This is the standard fix and the cleanest in most cases. IRC §408(d)(2)(A) explicitly excludes employer-plan dollars from the pro-rata aggregation pool. Most 401(k) plans accept incoming rollovers from traditional IRAs (check the plan document — it's not universal).

Procedure:

  1. Confirm your 401(k) plan accepts incoming rollovers (call HR or check the Summary Plan Description).
  2. Initiate a direct trustee-to-trustee transfer from your traditional IRA to the 401(k). Direct rollover avoids 60-day-rule and 20%-withholding complications.
  3. Confirm the rollover lands in the 401(k) BEFORE December 31 of the conversion year. Pro-rata is calculated on year-end balance.
  4. Then proceed with the backdoor Roth: nondeductible contribution to a clean traditional IRA, immediate conversion, file Form 8606.

Note: only PRE-TAX dollars roll into a 401(k). If your traditional IRA has both pre-tax and basis, only the pre-tax portion is rollable; the basis stays in the IRA. This "splits" the basis cleanly. After the rollover, the only IRA dollars left are basis — pro-rata calculates 100% basis, conversion is fully tax-free.

Path 2: Convert Everything

If your pre-tax IRA balance is small enough that paying the tax in one year is acceptable, just convert the whole pool. After the conversion, your IRA is empty, and any future backdoor Roth contribution is clean.

This works best when: your pre-tax balance is <$50K, you have low taxable income for the year (between jobs, sabbatical), or you're already planning Roth conversions for the next several years and want to consolidate.

Worked example: $30,000 pre-tax + $7,500 backdoor in same year = $37,500 conversion at 22% = $8,250 federal tax. Acceptable for some readers; prohibitive for others. Use the True Cost of a Conversion tool to see the full federal+state+IRMAA stack.

Path 3: Wait (or Don't Rollover)

If you anticipate leaving a job and rolling a pre-tax 401(k) into an IRA, that rollover would re-trigger pro-rata. Two pre-emptive options:

  • Don't roll the 401(k) into an IRA. Leave it at the former employer (if allowed) or roll into your new employer's 401(k). The dollars stay in employer-plan land, outside §408(d)(2).
  • Time the backdoor Roth before any pre-tax rollover. If you have no traditional IRAs today and no pre-tax 401(k) coming yet, do the backdoor Roth now. Once a pre-tax IRA balance exists, future backdoor Roths face pro-rata.

This requires planning ahead. Once a pre-tax balance is in a traditional IRA, it can't be rewound — you have to pay tax to clear it (Path 2) or roll into a 401(k) (Path 1).