You followed the steps exactly. In January you contributed $7,500 after tax to a — the 2026 limit under IRS Notice 2025-67 — and converted it to Roth a few days later, expecting a tax bill of zero. Then, at filing time, your preparer asks one question: "What was in your other IRAs on December 31?" The answer — a $95,000 rollover IRA left over from a residency employer plan — just made $6,951 of your conversion taxable. Nothing about the contribution or the conversion was executed wrong. The simply ran arithmetic you did not know was running.
This article makes that arithmetic explicit, works the $95,000 example line by line, and ranks the three fixes — because the rule is entirely fixable, usually without paying tax on anything. If the backdoor maneuver itself is new to you, start with the backdoor Roth module and come back; this article assumes you know the two steps and focuses on the rule that breaks them.
The pro-rata rule is arithmetic, not a penalty
The rule comes from how the IRS taxes IRA distributions and conversions (IRS Publication 590-B and ): for tax purposes, every traditional IRA dollar you own is one pot. You cannot point to the $7,500 you just contributed after tax and convert "those dollars." Each converted dollar is treated as a proportional slice of the whole pot — part after-tax basis, part pre-tax money — in the ratio the whole pot holds.
The taxable fraction of a conversion is computed as:
nontaxable fraction = your after-tax basis ÷ (December 31 value of all traditional, SEP, and SIMPLE IRAs + all distributions and conversions made during the year)
What counts in that denominator is specific, and worth a table:
| Account | Counts against your backdoor? |
|---|---|
| Traditional IRA (including rollover IRAs) | Yes |
| SEP IRA (including one from income) | Yes |
| SIMPLE IRA | Yes |
| Your spouse's IRAs | No — aggregation is per person |
| Inherited IRA you hold as a beneficiary | No — tracked on its own Form 8606 |
| , , 457(b), or other employer plan | No — plans are not IRAs |
The pro-rata rule aggregates every traditional, SEP, and SIMPLE IRA dollar you own — but only yours, and only IRAs. Your spouse's accounts and your employer plans are invisible to it. That last row is the entire escape route, and the fixes below run through it.
December 31 is the only date the formula sees
The denominator is not measured on the day you convert. It is measured on December 31 of the year of the conversion (Form 8606, line 6). This produces a timing trap that catches physicians in transition years: you can execute a perfectly clean conversion in March — zero other IRA money at that moment — and then poison it retroactively in November by rolling an old employer plan into a rollover IRA before year-end.
Important
The pro-rata calculation is retroactive to the whole calendar year. Converting first and cleaning up later does not work; the December 31 snapshot governs every conversion made that year. Two common ways physicians poison a conversion after the fact: rolling an old 403(b) or 401(k) into an IRA during a job change, and making a SEP IRA contribution for moonlighting income late in the year. Hold rollovers in the old plan, or roll them directly to the new employer plan, in any year you execute a backdoor Roth.
The same snapshot works in your favor: if pre-tax IRA money exists today, you have until December 31 of the conversion year to move it somewhere the formula cannot see.
The worked example: $95,000 of pre-tax money turns a $7,500 conversion into $6,951 of income
Example calculation
Assumptions, stated explicitly: you contribute $7,500 after tax to a traditional IRA in January 2026 and convert it within days, before any meaningful earnings. You also hold a $95,000 pre-tax rollover IRA, untouched all year. Marginal federal rate: 35 percent.
After-tax basis: $7,500 December 31 IRA value: $95,000 (rollover IRA) + conversions during the year: $7,500 Denominator: $95,000 + $7,500 = $102,500
Nontaxable fraction: $7,500 ÷ $102,500 = 0.0732 Nontaxable portion of the conversion: $7,500 × 0.0732 = $549 Taxable portion: $7,500 − $549 = $6,951
Federal tax at 35 percent: $6,951 × 0.35 ≈ $2,433
Note what did not happen: you were not fined, and no money vanished. The $6,951 of basis you could not use this year carries forward on Form 8606 (line 14) and offsets future distributions or conversions. But recovering it through the pro-rata formula takes years of partial credit — 92.7 percent of every future conversion remains taxable while the $95,000 sits there — so carrying basis forward indefinitely is bookkeeping, not a strategy. Fix the denominator instead.
Fix 1: roll the pre-tax IRA into your employer plan — usually the right move
Employer plans are not IRAs, so money inside a 401(k), 403(b), 401(a), or governmental 457(b) never enters the pro-rata denominator. Rolling the $95,000 into your current employer plan before December 31 empties the pot, and the backdoor conversion that same year computes against a denominator of $7,500 — fully nontaxable.
Two mechanical requirements decide whether this fix is available:
- The plan must accept incoming rollovers. The IRS permits plans to accept IRA roll-ins but does not require it. The answer is in the summary plan description, usually under "rollover contributions," or one call to the plan administrator. Most large hospital and university plans accept them; some small-group plans do not.
- Only pre-tax dollars may enter. The tax code bars after-tax IRA basis from rolling into an employer plan — and that restriction is exactly what makes the fix work. The pre-tax $95,000 leaves; any basis is legally required to stay behind in the IRA, where it converts tax-free once it is the only thing left.
Key insight
The direction of the transfer matters and is the entire fix. Plan-to-IRA rollovers create the pro-rata problem; IRA-to-plan rollovers remove it. If you executed the first by default at a job change — the standard advice from rollover paperwork — the second reverses it, at a cost of zero tax.
The honest trade-off: money in an employer plan is limited to that plan's investment menu and fee schedule. Before moving $95,000, compare the plan's fund expenses against what the IRA charges; a materially expensive plan can cost more over a decade than the backdoor saves. Where the employer plan sits in your overall account hierarchy is mapped in the retirement account map.
Fix 2: convert the entire balance and pay the tax — rational in specific years
If no employer plan will take the money — or the balance is small — convert all of it and end the problem permanently.
Example calculation
Assumptions, stated explicitly: $95,000 pre-tax rollover IRA, $7,500 of new basis, everything converted in the same year.
Taxable income created: $95,000 (the $7,500 of basis converts tax-free) Tax at a 35 percent marginal rate: $33,250 Tax at a 24 percent marginal rate (a fellowship or reduced-schedule year): $22,800
Same decision with a $6,000 stray IRA instead of $95,000: $6,000 × 0.35 = $2,100 — a one-time cost that permanently clears the denominator.
Whether this is rational is the standard conversion question — current versus expected rate in retirement — covered in Roth versus traditional arithmetic. In practice, the full conversion makes sense in two situations: the balance is small enough that the tax is a rounding error against decades of clean backdoor access, or you are sitting in a temporarily low bracket (final year of training, parental leave, sabbatical, a gap between positions). Paying 35 percent to convert $95,000 solely to enable a $7,500-per-year maneuver is rarely justified by the arithmetic; paying 24 percent in a fellowship year frequently is.
Fix 3: skip the backdoor — it is a maneuver, not a mandate
If the plan refuses roll-ins and a full conversion would land at your peak marginal rate, skipping the backdoor is a legitimate answer. The stakes are modest and worth stating plainly: the maneuver shelters $7,500 per year (2026 limit; $8,600 with the age-50 catch-up). Skipping a year while you change employers — most new employer plans accept roll-ins, so the problem is often temporary — costs you one year of tax-free growth on one contribution, not the strategy.
Meanwhile, larger Roth capacity may already exist in your employer plan: if it offers after-tax contributions with in-plan conversion, the mega backdoor Roth shelters multiples of the IRA limit without touching the pro-rata rule at all, because it never involves an IRA.
Form 8606 is the paper trail that keeps all of this tax-free
Every year you make a nondeductible contribution or a conversion, Form 8606 is required — one form per spouse, filed with your return. The mechanics, line by line:
- Line 1: the nondeductible contribution for the year ($7,500).
- Line 2: your basis carried forward from prior years. This line is why sloppy filing compounds: miss a year and your documented basis understates reality, and you pay tax twice on the same dollars.
- Line 6: the December 31 value of all traditional, SEP, and SIMPLE IRAs, plus any outstanding rollovers. This is the pro-rata trigger.
- Line 8: the amount converted to Roth during the year.
- The form divides basis by the aggregate (computed to at least three decimal places) to produce the nontaxable fraction, then carries unused basis forward on line 14.
- Part II, line 18: the taxable amount of the conversion, which flows to Form 1040 line 4b. A clean backdoor shows $0 here, or a few dollars of interim earnings.
The instructions attach a $50 penalty for failing to file a required Form 8606 and a $100 penalty for overstating basis, but the real cost of bad filing is the silent one: basis that goes unrecorded is basis that eventually gets taxed twice. Each spouse computes the rule independently on separate forms — a fact that cuts both ways, as the next section shows.
Quick takeaway
The pro-rata rule is a denominator problem, and you control the denominator until December 31 of the conversion year. Inventory every traditional, SEP, and SIMPLE IRA in your own name; roll pre-tax balances into an employer plan that accepts them; convert small remainders in low-bracket years; and file Form 8606 for every spouse, every year, without exception.
Common questions
My spouse has a $200,000 rollover IRA. Does it block my backdoor Roth?
No. The aggregation rule is computed per person, not per household. Your spouse's IRAs never enter your denominator, and each of you files a separate Form 8606. It does block your spouse's own backdoor contribution until fixed — so a two-physician couple can be half-clean and half-poisoned, filing from the same kitchen table.
Does my 403(b) or 401(k) balance count in the pro-rata calculation?
No. The formula aggregates traditional, SEP, and SIMPLE IRAs only. Employer plan balances — however large — are invisible to it, which is precisely why moving IRA money into a plan is the leading fix rather than a loophole.
I already converted this year and then remembered the rollover IRA. Is it too late?
No. The denominator is measured on December 31 of the conversion year, not on the conversion date. Roll the pre-tax IRA into an employer plan before year-end and the conversion you already executed computes against a clean denominator. This is the one place the retroactive rule works in your favor — but the roll-in must be complete, not merely initiated, by December 31, and transfers routinely take weeks. Do not start this in the last week of December.
What about the SEP IRA from my moonlighting income?
It counts, fully. A SEP contribution made for this year that sits in the account on December 31 enters the denominator, even if you contributed it after your conversion. Physicians with who want clean backdoor access typically use an individual 401(k) instead, since employer plans stay out of the formula — the trade-offs belong in a broader look at where each account fits.
What to do next
- List every traditional, SEP, and SIMPLE IRA in your name with its current balance — the five-minute inventory that decides everything else.
- Have your spouse run the same inventory separately; the rule is per person.
- If pre-tax balances exist, read your summary plan description or call the plan administrator and ask two questions: does the plan accept IRA rollovers, and what paperwork starts one.
- Compare the plan's fund expenses against your IRA before moving a large balance.
- Execute the roll-in — or a deliberate full conversion in a low-bracket year — with time to complete before December 31 of any year you convert.
- Calendar Form 8606 for every year with a nondeductible contribution or conversion, and confirm line 2 carries your full basis forward from last year's form.
The rule-year numbers here — the $7,500 limit, the phase-outs that make the backdoor necessary above $153,000 to $168,000 of modified AGI for single filers ($242,000 to $252,000 married filing jointly, per IRS Notice 2025-67) — reset annually, so verify them in any later year. The step-by-step execution sequence lives in the backdoor Roth walkthrough, and the checklist above works with or without us. This is education, not individualized financial advice.