Backdoor Roth IRA: A Complete Step-by-Step Guide

The backdoor Roth IRA has a slightly intimidating name for what is, mechanically, two ordinary and entirely legal steps: contribute to a Traditional IRA, then convert that contribution to a Roth IRA. High earners use it because it routes around the income limits that would otherwise block them from contributing to a Roth IRA directly. The strategy itself is simple. What actually causes problems is a single IRS rule, the pro-rata rule, that most explanations mention in passing but rarely walk through with real numbers. This guide does both: the step-by-step process, and a worked example of exactly where people get the tax bill wrong.

What a backdoor Roth IRA actually is

A backdoor Roth IRA is not a special account type. There's no "backdoor Roth IRA" application at a brokerage. It's a two-step sequence built on two provisions that have existed separately in the tax code for years. First, anyone with earned income can make a nondeductible contribution to a Traditional IRA, no matter their income. Second, anyone can convert Traditional IRA funds to a Roth IRA, also regardless of income, a restriction that was removed starting in 2010. Put those two facts together and you get a path into a Roth IRA for people whose income is too high to contribute directly. For background on how a Roth IRA works and what it's typically used for, see Traditional vs. Roth IRA for Index Investors and Index Funds in a Roth IRA.

Who this is actually for

This strategy is for people whose income exceeds the Roth IRA direct-contribution limits below, but who still want money growing inside a Roth IRA for its tax-free growth and tax-free qualified withdrawals. If your income already sits under the Roth IRA phase-out threshold, skip this entirely. Just contribute to a Roth IRA directly. It's simpler and avoids the pro-rata complexity altogether.

As a concrete example: a single filer earning $180,000 in 2026 is above the $168,000 upper phase-out threshold, so a direct Roth IRA contribution isn't available to them at all that year. A married couple filing jointly with a combined income of $270,000 is in the same position relative to the $252,000 threshold. Both could still contribute to a Traditional IRA on a nondeductible basis, since there's no income limit on that, and then convert to a Roth IRA. That's the backdoor Roth strategy in a sentence. Someone earning $140,000 as a single filer, by contrast, sits comfortably under the $153,000 threshold and can just contribute to a Roth IRA directly, no extra steps required.

2026 contribution limits and income thresholds

For the 2026 tax year, the IRA contribution limit is $7,500, or $8,600 if you're 50 or older, according to IRS Notice 2025-67. Direct Roth IRA contribution eligibility phases out as follows:

Notably, there's no income limit at all on making a nondeductible Traditional IRA contribution, and no income limit on converting Traditional IRA funds to a Roth IRA. That gap is exactly what the backdoor Roth strategy uses.

Timing: when during the year should you do this?

There's no single required timing, but a few practical points affect when investors typically move on each step. Contributing early in the year, rather than waiting until the following spring's filing deadline, gives the money more time invested and shrinks the window during which investment gains can build up in the Traditional IRA before conversion, since any such gains become taxable once converted. Some investors convert within days of contributing specifically to hold that gap close to zero. It's also worth knowing that the pro-rata calculation is based on your combined IRA balances as of December 31 of the conversion year, not the date of the conversion itself. That means a rollover into a 401(k) completed later in the same year can still clean up the pro-rata math for a conversion done earlier, as long as the pre-tax IRA balance is $0 by year-end. If you're also rolling over an old 401(k) balance, plan the sequence out in advance rather than doing it piecemeal.

The pro-rata rule — the part that trips people up

If you have no other money in any Traditional, SEP, or SIMPLE IRA, a backdoor Roth conversion is close to tax-free, since you're converting money you already paid income tax on before contributing. The complication shows up when you already hold pre-tax IRA money, commonly from an old 401(k) rollover. The IRS's pro-rata rule requires you to treat all your Traditional, SEP, and SIMPLE IRA balances as one combined pool when calculating the taxable portion of any conversion. You can't choose to convert just the after-tax slice while leaving the pre-tax portion behind, even if the money technically sits in different accounts.

Here's what that looks like with real numbers. Say you have $18,500 sitting in a Traditional IRA from an old 401(k) rollover, money that's never been taxed. You then open a new Traditional IRA and make a $7,500 nondeductible contribution for 2026, planning to convert it to a Roth IRA.

Instead of converting $7,500 tax-free as intended, roughly $5,337 of that conversion becomes taxable income for the year, because the IRS looks at the combined pool, not just the new contribution. This is the single most common reason people are blindsided by a tax bill after attempting a backdoor Roth, and it's entirely predictable in advance if you check your existing pre-tax IRA balances first.

Step-by-step: how to execute a backdoor Roth IRA

1. Check your existing pre-tax IRA balances first. Before anything else, add up any Traditional, SEP, and SIMPLE IRA balances you currently hold. This tells you whether the pro-rata rule will apply and roughly how much of your conversion will be taxable. Note that 401(k) and other employer-plan balances aren't part of this calculation, only IRAs are.
2. If you have existing pre-tax IRA balances and want to avoid the pro-rata rule, consider rolling them into a 401(k) first, assuming your current employer's plan accepts incoming rollovers. That empties your IRA pre-tax balance to $0, which is the cleanest way to keep a backdoor Roth fully tax-free going forward. Not every plan accepts rollovers-in, so confirm with your plan administrator before assuming it's an option.
3. Open a Traditional IRA if you don't already have one, ideally at the same brokerage where you'll hold your Roth IRA, to keep the conversion step simple.
4. Make a nondeductible contribution up to the annual limit ($7,500 for 2026, or $8,600 if 50+). Don't claim a tax deduction for it. The strategy depends on this being after-tax money.
5. Convert the Traditional IRA balance to a Roth IRA, usually a straightforward online request at your brokerage. Many investors convert within days of contributing specifically to minimize any investment gains that build up before conversion, since growth that occurs before conversion is taxable.
6. Invest the funds inside the Roth IRA according to your intended allocation. See Index Funds in a Roth IRA for how to think about fund selection once the money is there.
7. File Form 8606 with your tax return to report both the contribution and the conversion, covered in more detail below.

Married couples doing this together

Each spouse has their own separate IRA and their own separate pro-rata calculation. A spousal IRA, which lets a non-working or lower-earning spouse contribute based on the couple's joint income, follows the same rules described here. One spouse's existing pre-tax IRA balance doesn't affect the other spouse's pro-rata math at all, since the IRS treats each individual's IRAs as their own pool. This matters in practice: it's entirely possible for one spouse to have a clean, tax-free backdoor Roth conversion while the other spouse's conversion is partly taxable, simply because one of them happens to be carrying an old rollover balance and the other isn't. If you're doing this as a couple, it's worth running the numbers separately for each of you rather than assuming they'll look the same.

Form 8606: reporting it correctly

IRS Form 8606 ("Nondeductible IRAs") is how you report a nondeductible Traditional IRA contribution and track your basis, the after-tax amount the IRS already knows shouldn't be taxed again. The form has two relevant parts: Part I reports the nondeductible contribution, and Part II reports the conversion. If you contribute and convert in the same calendar year, which is what this guide recommends to minimize taxable growth before conversion, both parts go on a single Form 8606 filed with that year's tax return. If the contribution and conversion happen in different tax years, you'll file a Form 8606 covering each year separately. Skipping this form is one of the more consequential mistakes in this process. Without it, the IRS has no record that you already paid tax on the contribution, which can leave that same money effectively taxed twice if the gap isn't caught and corrected later. If you've made nondeductible contributions in past years without filing Form 8606, it's worth talking to a tax professional about filing the missing forms retroactively rather than leaving the gap in your records.

The mega backdoor Roth: a related but different strategy

The "mega backdoor Roth" gets confused with the standard backdoor Roth IRA fairly often, but it's a separate strategy. It uses after-tax contributions inside a 401(k) plan, not an IRA, and depends entirely on whether your specific employer's plan allows both after-tax contributions and in-plan Roth conversions, or in-service withdrawals to an outside Roth IRA. Not all plans allow this. It has to be confirmed directly with your plan administrator or plan documents. Where it's available, it can move much larger amounts into Roth status than the IRA-based version, bounded by the overall IRS Section 415(c) limit on combined employee and employer contributions to a defined contribution plan, which is $72,000 for 2026, or higher with age-based catch-up contributions. This is a meaningfully more complex strategy than the IRA-based backdoor Roth and depends heavily on plan-specific rules. See 401(k) Index Fund Options Explained for more on evaluating what your specific plan actually offers.

Common mistakes

• Not checking existing pre-tax IRA balances before converting. This is the single most common and most expensive mistake, since it turns the pro-rata tax bill into a surprise instead of a planned outcome.
• Claiming a tax deduction for the Traditional IRA contribution. This defeats the purpose. The strategy depends on the contribution being nondeductible so the later conversion isn't fully taxable.
• Letting significant investment gains build up before converting. Any growth in the Traditional IRA before conversion is taxable at conversion, which is why many investors convert soon after contributing.
• Forgetting to file Form 8606. Without it, there's no IRS record of your after-tax basis, which risks double taxation down the line.
• Assuming the conversion can be undone if something goes wrong. Roth conversions can't be recharacterized, or reversed, for tax years beginning in 2018 onward. Get the numbers right before converting, not after.

Is it worth the complexity?

For someone definitively locked out of direct Roth contributions by income, with no existing pre-tax IRA balances to complicate the pro-rata calculation, a backdoor Roth IRA is a relatively low-friction way to get money into tax-free growth. The mechanics take a bit more effort than a normal contribution, but the tax outcome ends up close to what a direct contribution would have looked like. It gets meaningfully more complicated, and worth a closer look, if you're carrying a large existing pre-tax IRA balance and don't have a 401(k) available to absorb it first. In that case, running the actual pro-rata math, as shown above, before converting is what determines whether the strategy is worth doing that year, or whether rolling the pre-tax balance into a 401(k) first is the smarter sequence. The general idea here is simple. The specific numbers are what matter. It's worth double-checking your own calculation, or having a tax professional confirm it, before you file.

Frequently Asked Questions

Summary

A backdoor Roth IRA is two legal, ordinary IRA transactions, a nondeductible contribution followed by a conversion, used together to get money into a Roth IRA despite exceeding the direct-contribution income limits. For 2026, those limits sit at $153,000–$168,000 for single filers and $242,000–$252,000 for married couples filing jointly, with a $7,500 contribution limit ($8,600 if 50+). The strategy itself is simple. The pro-rata rule is what actually demands attention, since any existing pre-tax IRA balance changes how much of the conversion ends up taxable, as the worked example above shows. Checking your existing IRA balances before you start, and filing Form 8606 correctly, are what separate a clean backdoor Roth from an unpleasant tax surprise.

Sources & References

• IRS Notice 2025-67 — 2026 Retirement Plan Contribution Limits
• IRS — About Form 8606, Nondeductible IRAs
• IRS — Traditional and Roth IRAs
• IRS — Retirement Topics: IRA Contribution Limits

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