The Pro-Rata Rule: The Backdoor Roth IRA Mistake that can Create an Unexpected Tax Bill

A backdoor Roth IRA can look simple on paper. You make a nondeductible contribution to a traditional IRA. Then you convert that money to a Roth IRA. Because you didn’t deduct the original contribution, you might expect little or no tax on the conversion.

But that may not be the result if you already have money in other IRAs.

The IRS generally doesn’t let you choose to convert only your after-tax IRA dollars while leaving your pre-tax IRA dollars untouched. Instead, the pro-rata rule can make part of the conversion taxable.

This can come as a surprise if you have an old rollover IRA, SEP IRA, or SIMPLE IRA in addition to the account you’re using for a backdoor Roth strategy.

Before you make the contribution or conversion, you need to know what other IRA balances could affect the calculation.

A $7,500 conversion may not mean $7,500 comes out tax-free

Consider a simplified example:

You earn too much to make a direct Roth IRA contribution, so you contribute $7,500 to a traditional IRA and don’t take a tax deduction for the contribution. You then convert the $7,500 to a Roth IRA.

You might expect the conversion to create little or no taxable income because you already paid income tax on the $7,500 you contributed. But suppose you also have $92,500 of pre-tax money sitting in a rollover IRA from a former employer’s 401(k).

Based on this example, you now have:

• $7,500 of after-tax basis
• $92,500 of pre-tax IRA money
• $100,000 total

Your after-tax basis represents 7.5% of that total IRA balance.

In general, you can’t simply designate the $7,500 conversion as coming entirely from the $7,500 you just contributed. The pro-rata calculation determines how much of the conversion represents after-tax basis and how much represents pre-tax money.

Assuming there are no earnings, losses, or other IRA distributions during the year, about 7.5% of the $7,500 conversion, or roughly $562, would represent after-tax basis. The remaining $6,938 would generally be taxable.

Before using a backdoor Roth strategy, list your existing IRA balances and identify how much is pre-tax and how much is after-tax basis.

Opening a separate IRA doesn’t necessarily fix the problem

Keeping the new contribution in a separate account generally doesn’t let you avoid the pro-rata calculation.

Suppose your $92,500 rollover IRA is at one financial institution. You open a new traditional IRA somewhere else, contribute $7,500, and convert only that account.

The accounts are physically separate. But the tax calculation generally doesn’t treat them that way.

When you make nondeductible IRA contributions or Roth conversions, Form 8606 is used to report those transactions and determine how much of an IRA distribution or conversion is taxable. For that calculation, your traditional IRAs are generally considered together. Traditional SEP IRAs and traditional SIMPLE IRAs are generally included as well.

So if you have $92,500 of pre-tax money in one IRA and a $7,500 nondeductible contribution in another, opening the second account does not necessarily change the pro-rata result. Moving the new contribution to another custodian doesn’t make the old IRA disappear from the tax calculation.

Before opening another IRA specifically for a backdoor Roth conversion, review all of your traditional, traditional SEP, and traditional SIMPLE IRA balances.

Your 401(k) is different from your IRA for this calculation

The aggregation rule is broad, but it doesn’t include every retirement account you own. For example, money that remains in a 401(k) generally isn’t included in the IRA pro-rata calculation.

Let’s say you have $500,000 in a former employer’s 401(k), no pre-tax traditional IRA balances, and a $7,500 nondeductible traditional IRA contribution. The $500,000 in the 401(k) generally isn’t included in the IRA pro-rata calculation while it remains in the 401(k).

Now change one fact.

Suppose you roll that $500,000 from the 401(k) into a traditional rollover IRA. That could change the pro-rata calculation substantially. Your investments might look nearly identical before and after the rollover. But the type of account holding those investments has changed, and that can change the tax result.

If you’re considering both a 401(k) rollover and a backdoor Roth strategy, review the two decisions together before moving the money.

December 31st can matter more than the day you make the conversion

It’s easy to focus only on the day you complete the Roth conversion, but the year-end IRA balance can matter too.

Form 8606 generally uses the value of all of your traditional IRAs as of December 31st as part of the pro-rata calculation. It also takes into account other relevant IRA distributions and conversions during the year.

Suppose you make a nondeductible IRA contribution and complete a Roth conversion in March. At that point, you don’t have another traditional IRA balance. Then, in November, you leave your job and roll your old 401(k) into a traditional IRA. You might assume the November rollover has nothing to do with the Roth conversion you completed months earlier – but because the IRA balance exists at year-end, it can affect the calculation.

This is why a backdoor Roth conversion shouldn’t always be viewed as a one-day transaction. You need to consider what your IRA picture may look like at the end of the tax year. If you’re considering both a Roth conversion and another retirement account rollover during the same year, review the two decisions together before moving the money.

Form 8606 is what connects the strategy to your tax return

A nondeductible IRA contribution creates basis in your traditional IRA.

That basis matters because you’ve already paid income tax on those dollars. Form 8606 reports nondeductible traditional IRA contributions and helps determine how much of a later IRA distribution or Roth conversion is taxable.

In practical terms, your nondeductible contribution creates after-tax basis. When you later convert money to a Roth IRA, Form 8606 is used to determine how much of that conversion comes from after-tax basis and how much is taxable.

The key is that your basis isn’t necessarily tied permanently to the particular dollars sitting in one account. If the pro-rata calculation means only part of your basis is applied to this year’s conversion, the unused basis generally carries forward. That makes recordkeeping important.

For example, suppose prior tax returns show $20,000 of traditional IRA basis that hasn’t yet been recovered. That amount could affect the tax treatment of a conversion you make this year.

Don’t rely on your brokerage statement to tell you your tax basis. Review prior Forms 8606 and your tax records before estimating the taxable portion of a conversion.

A pre-tax IRA doesn’t automatically mean you should abandon the strategy

Discovering a large pre-tax IRA doesn’t automatically mean a Roth conversion is a bad idea. It means you have another planning issue to work through first.

Depending on your situation, one option may be to determine whether an employer retirement plan can accept eligible pre-tax IRA money. Another possibility is intentionally converting some pre-tax IRA money as part of a broader Roth conversion strategy. In other cases, it may make more sense to reconsider the timing of the backdoor Roth contribution and conversion.

Each choice can have consequences beyond the pro-rata calculation.

For example, an employer plan may not accept the rollover you’re considering. A larger Roth conversion can increase taxable income substantially. Moving money between accounts can also affect investment choices, fees, and future distribution planning.

There is no single fix that works for everyone with a pre-tax IRA. Before moving money, compare the tax result under the options that are actually available to you.

Review the full IRA picture before you convert

The pro-rata rule can create the biggest surprise when you learn about it after the transaction is already complete. That’s especially important because a completed Roth conversion generally can’t be recharacterized back to a traditional IRA.

Before using a backdoor Roth IRA strategy, ask:

• Do you have money in any traditional IRAs, including rollover IRAs?
• Do you have a traditional SEP IRA or traditional SIMPLE IRA?
• Have you made nondeductible IRA contributions in prior years?
• Are you carrying forward basis from prior Forms 8606?
• Are you planning a 401(k) rollover or another retirement account transaction before December 31st?
• What are your applicable IRA balances likely to look like at year-end?

If you have several retirement accounts, old IRA basis, or a planned rollover, it’s worth running the numbers before completing the conversion. A transaction that appears tax-free when you look at one account can look very different once all of the applicable IRA balances are included.

For more personalized guidance, please contact our office.

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