Clearing Pre-Tax IRA Money Before a Backdoor Roth: The December 31 Fix

Updated August 2, 2026. Quick answer: the pro-rata rule is usually described as something that happens to you. It is not. The fraction that decides how much of your backdoor Roth is taxable is measured on 31 December, not on the day you convert — so you have until the end of the year to change the number it is measured against. The standard fix is to move your pre-tax IRA money into an employer 401(k), which is not an IRA and therefore does not count.

Why moving money into a 401(k) works

Two provisions do all the work together. First, the aggregation rule — you do not get to point at one clean IRA and convert that:

“all individual retirement plans shall be treated as 1 contract, … all distributions during any taxable year shall be treated as 1 distribution, and … the value of the contract … shall be computed as of the close of the calendar year”

IRC § 408(d)(2)

Note the third limb, which is the one almost nobody quotes: the value is computed as of the close of the calendar year. Form 8606 asks the same question in plainer words — “Enter the total value of all your traditional IRAs as of December 31, 2025, plus any outstanding rollovers.” So a balance you carried for eleven months and cleared in December is not in the fraction. A balance you created in December is.

Second, what “all individual retirement plans” actually covers. The IRS is explicit that “The term ‘traditional IRA’ includes traditional SEP IRAs and traditional SIMPLE IRAs”, so a forgotten SEP from a consulting year counts. Roth IRAs do not: “Section 408(d)(2) shall be applied separately with respect to Roth IRAs and other individual retirement plans.” (IRC § 408A(d)(4)(A)). And an employer plan is not an individual retirement plan at all — which is the door.

The move

1. Confirm your 401(k) accepts incoming rollovers from an IRA. This is a plan feature, not a right: “You may be able to roll over, tax free, a distribution from your traditional IRA into a qualified plan. … The part of the distribution that you can roll over is the part that would otherwise be taxable (includible in your income). Qualified plans may, but aren’t required to, accept such rollovers.” (IRS Publication 590-A). Ask for it in writing before you start anything else, because the whole plan depends on it and roughly nothing else here is reversible on a deadline.
2. Roll the pre-tax balances in. Traditional, rollover and SEP IRAs. Direct trustee-to-trustee, so nothing is withheld and no 60-day clock starts.
3. Leave the basis behind. You have no choice, and it is the point — see below.
4. Then do the backdoor conversion, with the pre-tax IRA balance at zero on 31 December.

The detail that makes this elegant rather than merely clever

“the entire amount received … is paid into an eligible retirement plan … except that the maximum amount which may be paid into such plan may not exceed the portion of the amount received which is includible in gross income”

IRC § 408(d)(3)(A)(ii)

Only the taxable portion may go into the employer plan. Your after-tax basis is legally barred from following it. People read that as a restriction; for this manoeuvre it is exactly the outcome you want. The pre-tax money leaves, the basis cannot, and what remains in the IRA is all basis — so converting it is tax-free rather than nearly tax-free.

Four ways this goes wrong

• A SIMPLE IRA inside its first two years. The statute is unusually blunt: a distribution in that window “In the case of any payment or distribution out of a simple retirement account … this paragraph shall not apply unless such payment or distribution is paid into another simple retirement account.” (IRC § 408(d)(3)(G)). It cannot go to your 401(k) and it cannot go to a traditional IRA. Worse, the early-distribution penalty in that window is charged “during the 2-year period beginning on the date such individual first participated in any qualified salary reduction arrangement maintained by the individual’s employer … paragraph (1) shall be applied by substituting ’25 percent’ for ’10 percent’” (IRC § 72(t)(6)(A)). If a SIMPLE is in the picture and the two years are not up, this cleanup does not work this year. Wait.
• Doing it in the wrong order, or too late. The rollover must land before 31 December — not be initiated before it. Custodian transfers routinely take weeks, and the last two weeks of December are the worst possible time to discover a paperwork requirement.
• Rolling an old 401(k) out to an IRA in the same year. This is the quiet self-inflicted version: a job change, a helpful rollover into an IRA in November, and a pro-rata denominator created out of nothing on 31 December. If a backdoor Roth is part of your annual routine, an old employer plan is better left where it is or moved to your current plan.
• Assuming your spouse’s balances matter. They do not, in either direction: “If both you and your spouse are required to file 2025 Form 8606, file a separate 2025 Form 8606 for each of you.” The calculation is per person. One spouse can have a large pre-tax IRA and the other a perfectly clean backdoor in the same household.

When not to bother

This is a real amount of administration for a specific benefit, and it is not always worth it. If your pre-tax IRA balance is small relative to the conversion, the tax the pro-rata rule creates may be less than the friction of moving accounts — and paying it simply gets you basis you will recover later anyway. Run the number before deciding: the pro-rata calculator gives the taxable percentage and the dollar cost at your bracket, which is the figure this decision should turn on.

The other case for leaving it alone: an employer plan with poor investment options and high fees. Moving a large IRA into a bad 401(k) to save a modest one-off tax is a trade people regret for years. Check what the plan actually charges first — what a fee difference costs over time is usually the larger number.

Where this sits

The pro-rata calculator tells you what the rule costs you as things stand; this page is how you change the input. If you are converting an existing balance rather than contributing, that is a different decision with different arithmetic — whether a conversion pays and how much fits in your bracket.

And if you are a high earner still accumulating, the contribution side has its own stack: what the catch-up allowances are worth.

Aggregation and the year-end valuation from IRC § 408(d)(2); the Roth carve-out from § 408A(d)(4)(A); the rollover limit from § 408(d)(3)(A)(ii); the SIMPLE two-year restrictions from §§ 408(d)(3)(G) and 72(t)(6)(A); plan-acceptance and the per-person filing rule from IRS Publication 590-A and the Instructions for Form 8606. All read August 2026. General information, not tax advice — and the order of operations here is unforgiving, so it is worth confirming with whoever prepares your return before you move anything.