Backdoor Roth IRA: What It Is and How to Do It Step by Step

The Roth IRA is one of the most powerful tax-advantaged accounts in the American retirement system: contributions go in after-tax, growth is completely tax-free, withdrawals in retirement are tax-free, and there are no required minimum distributions during the owner's lifetime. The problem is that Congress put an income ceiling on direct Roth contributions. In 2026, single filers with MAGI above $165,000 and married filers above $246,000 can't contribute to a Roth at all — at least not directly. But there's a fully legal workaround that the IRS has explicitly acknowledged: the backdoor Roth IRA conversion. Here's exactly how it works, where it can go wrong, and who benefits most.

Why the Backdoor Strategy Exists

Roth IRA direct contributions are limited by income. For 2026, the phase-out begins at $150,000 for single filers and $236,000 for married filing jointly, with contributions completely eliminated above $165,000 (single) and $246,000 (MFJ). But the tax code contains a separate and important distinction: while there's an income limit on Roth contributions, there is no income limit on Roth conversions. Anyone, regardless of income, can convert money from a traditional IRA to a Roth IRA. The backdoor strategy exploits exactly this gap — you make a non-deductible traditional IRA contribution (which has no income limit) and then immediately convert it to a Roth (which also has no income limit). The result is money in a Roth account despite being above the direct contribution income cap.

The Two-Step Process

Step 1: Make a non-deductible traditional IRA contribution. Open or use an existing traditional IRA account and contribute up to $7,000 for 2026 ($8,000 if you're age 50 or older). Because your income exceeds both the Roth contribution limit and the traditional IRA deduction limit (assuming you have a workplace plan), this contribution is after-tax and non-deductible. You've already paid income tax on this money — it's your basis in the account.

Step 2: Convert the traditional IRA to a Roth IRA. Shortly after making the contribution — ideally within the same week — instruct your brokerage to convert the traditional IRA balance to your Roth IRA. Because you just contributed the money and it's sitting in cash or a money market fund before being invested, there are no or minimal investment gains in the account. Since you already paid tax on the contribution, and there's nothing to tax on the negligible gains, the conversion is nearly tax-free. Your brokerage will issue a Form 1099-R showing the conversion; you report it on Form 8606 on your tax return.

The Pro-Rata Rule: The Critical Trap

Here's where many people get blindsided. The IRS does not allow you to cherry-pick which dollars you're converting. If you have any pre-tax money sitting in any traditional IRA — a rollover IRA from an old 401(k), a SEP-IRA, a SIMPLE IRA, or a previously deductible traditional IRA — the agency treats all of your traditional IRA assets as a single commingled pool when calculating the taxable portion of a conversion. This is the pro-rata rule, and it effectively taxes a portion of your conversion based on the ratio of pre-tax money to total IRA money.

Here's a concrete example of how damaging this can be. Suppose you have a $50,000 rollover IRA from a prior employer's 401(k) — all pre-tax dollars. You make a $7,000 non-deductible traditional IRA contribution and then try to convert just that $7,000. The IRS looks at your total traditional IRA balance: $57,000. Of that, $7,000 is after-tax basis, or 12.3%. The remaining $50,000 (87.7%) is pre-tax. When you convert $7,000, only 12.3% — about $861 — is tax-free. The other $6,139 is taxable income. The backdoor is largely defeated by the existing pre-tax IRA balance.

How to Fix the Pro-Rata Problem

The solution is to eliminate your pre-tax traditional IRA balances before doing the backdoor conversion. The cleanest way to do this is to roll your pre-tax traditional IRA into your current employer's 401(k) plan — if the plan accepts incoming rollovers, which most do. Employer 401(k) assets are excluded from the pro-rata calculation entirely. Once your rollover IRA balance is $0, you can make the backdoor contribution and convert it with a clean slate, and the full conversion will be tax-free (aside from any minimal investment gains that occurred between contribution and conversion).

Note that this only works if your employer's 401(k) accepts rollovers from IRAs and if the plan allows this type of transfer. Check with your HR department or plan administrator. If rolling to a 401(k) isn't possible and you have a large pre-tax IRA balance, the backdoor strategy may not be worth executing — the tax cost of the pro-rata calculation could outweigh the benefit.

Form 8606: The Required Paperwork

Every year you make a non-deductible IRA contribution, you must file Form 8606 (Nondeductible IRAs) with your tax return. Part I documents your non-deductible contribution and cumulative basis. Part II documents the Roth conversion and the taxable and non-taxable amounts. This form is how the IRS knows your basis in your traditional IRAs — without it, there's no official record that you already paid tax on the contributed funds, and you risk being taxed on the same money again when you take withdrawals in retirement.

Keep copies of every Form 8606 you ever file, indefinitely. Your basis accumulates over years of non-deductible contributions, and it carries forward through account consolidations and rollovers. If you've been making non-deductible contributions for years without filing Form 8606, you can file late forms for prior years to establish your basis — consult a tax professional if this applies to you.

Timing: When to Execute the Conversion

The conventional wisdom is to convert as quickly as possible after the initial contribution — ideally within a few days, and certainly within the same calendar year. The reason is simple: any investment gains that accumulate between contribution and conversion are pre-tax earnings, and those gains become taxable income at conversion. If you contribute in January and wait until December to convert, and your $7,000 grew to $7,400, you owe ordinary income tax on $400. Converting immediately when the account holds only cash eliminates this issue almost entirely.

Some people prefer to contribute to the traditional IRA in January for the prior tax year and then convert immediately in the new year, keeping the contribution and conversion in different calendar years for accounting clarity. This works fine as long as you convert promptly and report both actions correctly on their respective tax year returns. What doesn't work cleanly is contributing in one year, waiting months for the account to grow, and then converting — you'll have a taxable gain component that complicates the math and increases your tax bill.

Is the Backdoor Roth Legal?

Yes, unambiguously. The IRS has explicitly acknowledged the backdoor Roth conversion strategy in multiple publications and has taken no regulatory action against it. Congress is aware of it — the Build Back Better Act proposed in 2021 included provisions to ban backdoor and mega backdoor conversions for high earners, but those provisions were not enacted. As of 2026, the strategy remains fully permissible under current law. There is always legislative risk that Congress could restrict it in the future, but retroactive prohibition would be unusual and politically difficult.

MAGI	Direct Roth Contribution	Backdoor Roth	Notes
Below $150,000 (single)	Full $7,000 allowed	Available but unnecessary	Contribute directly
$150,000–$165,000 (single)	Partial contribution	Available	Use direct first, backdoor for remainder
Above $165,000 (single)	Not allowed	Available	Use backdoor
Below $236,000 (MFJ)	Full $7,000 allowed	Available but unnecessary	Contribute directly
$236,000–$246,000 (MFJ)	Partial contribution	Available	Backdoor for remainder
Above $246,000 (MFJ)	Not allowed	Available	Full backdoor strategy

The Mega Backdoor Roth: A Much Larger Opportunity

For those whose employer's 401(k) plan supports it, the mega backdoor Roth is an even more powerful extension of the same concept. Here's how it works: most 401(k) plans allow only traditional (pre-tax) or Roth employee contributions up to $23,500 in 2026. But the total annual limit on all contributions to a 401(k) — employee contributions plus employer match plus after-tax contributions — is $70,000. If your plan allows after-tax (non-Roth) contributions and either in-plan Roth conversions or in-service withdrawals, you can contribute after-tax dollars beyond the regular $23,500 limit and then convert them to Roth, either within the plan or by rolling them out to a Roth IRA.

To illustrate: say you contribute $23,500 in traditional 401(k) contributions, your employer adds a $10,000 match, and your plan allows after-tax contributions. The remaining contribution room is $70,000 − $23,500 − $10,000 = $36,500. You can contribute that $36,500 after-tax and immediately convert it to Roth. The result is $36,500 more in Roth savings that year on top of the $7,000 from the backdoor IRA — far more than direct Roth IRA contributions alone would allow. This strategy requires checking whether your specific 401(k) plan document permits after-tax contributions and in-plan Roth conversions; many plans don't. Ask your HR department or plan administrator for the plan's Summary Plan Description.

Who Benefits Most from the Backdoor Roth

The backdoor Roth is most valuable for dual high-income earners above the Roth income limits who have no pre-tax IRA balances (or can roll them to a 401(k)); younger high earners who want decades of compounding tax-free growth; people seeking tax diversification in retirement — a mix of pre-tax (401k), taxable, and tax-free (Roth) accounts provides maximum flexibility; and anyone who expects future tax rates to be as high or higher than current rates, making tax-free withdrawal more valuable. It's less useful for those who cannot clear pre-tax IRA balances due to plan restrictions, those in very low current tax brackets where the Roth's tax-free withdrawal advantage is minimal, and those who expect to be in a much lower bracket in retirement, where tax-deferred traditional accounts produce a better outcome.