The backdoor Roth IRA sounds simple. Make a nondeductible contribution to a Traditional IRA, convert it to a Roth, and pay little or no tax on the move. High earners use it every year to get money into a Roth IRA even when their income is too high to contribute directly.
But there's a catch that trips up more people than almost any other retirement strategy. It's called the pro rata rule, and if you have any pre-tax money sitting in an IRA anywhere, it can turn your "tax-free" backdoor Roth into a surprise tax bill.
Let's walk through how it works, with real numbers.
First, a Quick Refresher on the Backdoor Roth
For 2026, you can't contribute directly to a Roth IRA once your modified adjusted gross income passes $168,000 as a single filer or $252,000 as a married couple filing jointly.¹
Here's the workaround. There's no income limit on contributing to a Traditional IRA, and there's no income limit on converting a Traditional IRA to a Roth IRA. So a high earner can:
- Contribute up to $7,500 to a Traditional IRA ($8,600 if age 50 or older) as a nondeductible contribution¹
- Convert that money to a Roth IRA
- Report it all on IRS Form 8606²
Since the contribution was made with after-tax dollars, converting it shouldn't create much of a tax bill. In a perfect world, the only taxable amount is whatever growth occurred between the contribution and the conversion.
That's the perfect world. The pro rata rule is what happens in the real world.
What Is the Pro Rata Rule?
The pro rata rule says you can't cherry-pick which dollars you convert.
When you convert money from a Traditional IRA to a Roth IRA, the IRS looks at all of your Traditional, SEP, and SIMPLE IRAs combined as one big bucket.² It doesn't matter that your nondeductible contribution sits in a brand new account at one custodian while your old rollover IRA sits at another. For tax purposes, it's all one pool of money.
Your conversion is then treated as coming proportionally from the pre-tax and after-tax dollars in that pool. If 90% of your combined IRA money is pre-tax, then 90% of your conversion is taxable. Period.
The math happens on Form 8606, and it uses the value of all your Traditional, SEP, and SIMPLE IRAs as of December 31 of the year you convert.² That December 31 date matters more than most people realize, and we'll come back to it.
Example 1: The Clean Backdoor Roth
Sarah earns too much to contribute directly to a Roth IRA. She has a 401(k) at work but no money in any Traditional, SEP, or SIMPLE IRA.
In January, she contributes $7,500 to a Traditional IRA as a nondeductible contribution. A few days later, before the money has earned anything, she converts the full $7,500 to her Roth IRA.
Her pro rata math:
- After-tax basis: $7,500
- Total IRA value on December 31 (plus the conversion): $7,500
- After-tax percentage: 100%
Taxable amount of the conversion: $0.
This is the backdoor Roth working exactly as intended. Because Sarah had no other IRA money, every dollar she converted was after-tax. Her 401(k) doesn't count against her, since employer plans like 401(k)s, 403(b)s, and 457 plans are not included in the pro rata calculation.²
Example 2: The Rollover IRA That Ruins Everything
Now meet Dave. Dave also earns too much for a direct Roth contribution. A few years ago, he rolled an old 401(k) into a Traditional IRA, and that account is now worth $67,500. All of it is pre-tax money.
Dave reads about the backdoor Roth and contributes $7,500 to a new Traditional IRA as a nondeductible contribution. He converts that $7,500 to a Roth, assuming it's tax-free since he's only converting the new account.
Here's what actually happens on Form 8606:
- After-tax basis: $7,500
- Total Traditional IRA value on December 31 plus the amount converted: $67,500 + $7,500 = $75,000
- After-tax percentage: $7,500 ÷ $75,000 = 10%
Only 10% of Dave's $7,500 conversion is tax-free. That's $750. The other $6,750 is taxable income, taxed at his ordinary income rate.
If Dave is in the 32% federal bracket, that's roughly $2,160 in federal tax on a move he thought was free. Depending on where you live, your state income tax may add to that as well.
And here's the part that surprises people: Dave doesn't lose his remaining $6,750 of after-tax basis. It stays behind in his IRA and carries forward on Form 8606 to reduce taxes on future distributions or conversions.² But it's now diluted across his entire IRA balance, which defeats the whole point of the quick, clean backdoor Roth.
Example 3: The December 31 Trap
This one catches even people who think they've done everything right.
Maria has no IRA balances at all. In February, she does a textbook backdoor Roth: contributes $7,500, converts it immediately, pays no tax. Clean.
Then in October, she changes jobs and rolls her old $150,000 401(k) into a Traditional IRA.
Remember, Form 8606 uses your total IRA balance as of December 31 of the conversion year.² It doesn't matter that Maria's IRA was empty back in February when she converted. On December 31, she has $150,000 of pre-tax money sitting in a Traditional IRA.
Her pro rata math for the year:
- After-tax basis: $7,500
- December 31 IRA value plus conversion: $150,000 + $7,500 = $157,500
- After-tax percentage: about 4.8%
Suddenly, roughly 95% of her February conversion is taxable. A rollover decision made in October reached back and changed the tax treatment of a conversion she completed eight months earlier.
The lesson? If you're planning a backdoor Roth, think about the entire calendar year before moving any retirement money into an IRA.
What Doesn't Count in the Pro Rata Calculation
A few important exclusions:
- Employer plans. Balances in 401(k)s, 403(b)s, and 457 plans are not part of the calculation.²
- Roth IRAs. Existing Roth balances don't count.
- Your spouse's IRAs. The pro rata rule is applied per person, not per household. If your spouse has a large pre-tax IRA but you don't, your backdoor Roth is unaffected by their accounts. Each spouse files their own Form 8606.²
- Inherited IRAs. IRAs you inherited as a beneficiary are generally tracked separately from your own IRAs for basis purposes.²
Ways to Work Around the Pro Rata Rule
There's no loophole that lets you ignore the rule. But there are several planning approaches that can reduce its impact or avoid it entirely.
1. Convert the entire pre-tax balance and clear the deck.
The pro rata rule only bites when pre-tax money is left sitting in your IRAs on December 31. One option is to convert the whole thing. Yes, you'll pay tax on the full pre-tax amount, but you pay it once, and every backdoor Roth after that is clean.
This works best when the pre-tax balance is modest, or when you're in a lower-income year and the conversion fills up a tax bracket you're comfortable with. For larger balances, spreading conversions over several years can keep you from jumping into a higher bracket. We covered when conversions make sense in our earlier post on Roth conversions.
2. Use the spouse with no IRA balances.
The pro rata rule is applied per person, not per household. If you have a large rollover IRA but your spouse has no Traditional, SEP, or SIMPLE IRA money, your spouse can do a clean backdoor Roth even though you can't.²
As long as the household has enough earned income, each spouse can contribute up to their own limit ($7,500 for 2026, or $8,600 at age 50 or older).¹ That's real money into a Roth every year while you work on a longer-term plan for your own pre-tax balance.
3. If you're self-employed, watch which accounts you feed.
SEP IRAs and SIMPLE IRAs count in the pro rata calculation.² Every year you contribute to one, you're growing the pre-tax pool that dilutes your backdoor Roth. Business owners who want to keep the backdoor open often look at a solo 401(k) for their retirement plan contributions instead, since employer plan balances aren't part of the calculation. Which plan fits best depends on your business, so this is worth mapping out before you set anything up.
4. See if your 401(k) offers a different door entirely.
Some employer plans allow after-tax contributions above the regular deferral limit, up to the overall plan limit of $72,000 for 2026.³ If the plan also allows those after-tax dollars to be converted to Roth (either inside the plan or rolled out to a Roth IRA), that's often called a mega backdoor Roth.
Here's why it matters for this conversation: that strategy happens entirely inside the employer plan, so your IRA balances and the IRA pro rata rule don't get in the way. Not every plan offers these features, so check your plan documents or ask your plan administrator.
5. Skip the backdoor and use a taxable brokerage account.
Sometimes the cleanest answer is to stop forcing the Roth and invest the money in a regular, non-qualified brokerage account instead.
A taxable account has no income limits, no contribution limits, and no waiting until 59½ to touch your money. And while it doesn't offer tax-free growth like a Roth, the tax treatment is friendlier than most people assume. Investments held longer than a year are taxed at long-term capital gains rates of 0%, 15%, or 20% depending on your income, and qualified dividends get those same preferential rates.⁴ Compare that to IRA withdrawals, which are taxed as ordinary income at rates as high as 37%.
You also get flexibility a retirement account can't match: the ability to harvest losses against gains, no required minimum distributions, and under current law, a step-up in cost basis for your heirs.
The tradeoffs are real, though. Interest and short-term gains are still taxed at ordinary rates, dividends create some tax drag each year, and higher earners may also owe the 3.8% net investment income tax. For many high earners with a pro rata problem, a low-turnover, tax-efficient portfolio in a taxable account ends up being a strong companion to their retirement accounts rather than a consolation prize.
6. Accept the tax if a conversion fits your plan anyway.
The pro rata rule doesn't prohibit anything. It just determines how much of a conversion is taxable. Some people knowingly convert a mix of pre-tax and after-tax dollars because a Roth conversion makes sense for their broader plan anyway, especially in lower-income years between retirement and Social Security or required minimum distributions.
The problem isn't paying tax on a conversion. The problem is paying tax you didn't expect, at a rate you didn't plan for, in a year when your income was already high.
The Bottom Line
The backdoor Roth is a legitimate, widely used strategy. But it only works cleanly when your Traditional, SEP, and SIMPLE IRA balances are at or near zero on December 31 of the conversion year.
Before you make that nondeductible contribution, take inventory. Old rollover IRAs, SEP IRAs from a side business, and SIMPLE IRAs from a former employer all count. And remember that Form 8606 is required any year you make a nondeductible contribution or take a distribution with basis, so keep those forms with your permanent tax records.²
At Dreyer Wealth Management, we help clients map out the sequence of contributions, rollovers, and conversions so the December 31 snapshot works in their favor, and we coordinate with your tax professional on the reporting. If you're wondering whether a backdoor Roth fits your situation, or whether an old IRA is standing in the way, give our office a call at (920) 380-7056 or email hello@dreyerwealth.com. We're happy to take a look.
This material is for general educational purposes only and is not intended as tax or legal advice. Tax laws are subject to change. Please consult your tax professional regarding your individual situation before implementing any strategy discussed here. A Roth conversion is a taxable event and may have additional tax consequences. Whether a conversion is appropriate depends on your individual circumstances.
Sources
- Internal Revenue Service, "401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500" (IR-2025-111, Nov. 13, 2025): https://www.irs.gov/newsroom/401k-limit-increases-to-24500-for-2026-ira-limit-increases-to-7500
- Internal Revenue Service, Instructions for Form 8606, Nondeductible IRAs: https://www.irs.gov/instructions/i8606
- Internal Revenue Service, Notice 2025-67 (2026 cost-of-living adjustments for retirement plans, including the Section 415(c) defined contribution limit): https://www.irs.gov/pub/irs-drop/n-25-67.pdf
- Internal Revenue Service, Topic No. 409, Capital Gains and Losses: https://www.irs.gov/taxtopics/tc409