How a backdoor Roth conversion actually works

A backdoor Roth is a two-step process: you put money into a traditional IRA, then convert that money to a Roth IRA. The IRS allows this conversion even if your income is too high to contribute directly to a Roth. You do not need permission from anyone — you straightforward execute the steps yourself through your brokerage or bank.

The conversion itself is not complicated. The hard part is understanding the tax bill that comes with it, and making sure you do not accidentally trigger the pro-rata rule, which can make the conversion much more expensive than you expected.

The timeline matters: you typically contribute to the traditional IRA in one tax year, then convert it in the same year or early in the next year, before the IRS filing important date. The conversion is reported on Form 8606, which you file with your tax return.

Key Takeaways

  • A backdoor Roth requires two separate transactions: a non-deductible contribution to a traditional IRA, then a conversion of that money to a Roth IRA.
  • You must report the contribution on Form 8606 in the year you make it, even though you get no tax deduction, or the IRS will assume the money is deductible and tax you twice.
  • If you have any other traditional, SEP, or straightforward IRAs with a balance, the pro-rata rule applies to your entire conversion, potentially creating a large tax bill on money you thought was tax-free.
  • The conversion itself creates a tax bill in the year you convert, based on how much of the converted money represents gains or deductible contributions from other IRAs.
  • You can do a backdoor Roth in the same calendar year you do a Roth conversion, but doing both in one year can trigger the pro-rata rule across both transactions.

Step 1: Contribute money to a traditional IRA

Open or use an existing traditional IRA at a brokerage, bank, or investment firm. The account must be in your name. You then deposit cash into it — the amount is up to you, though the IRS sets an annual limit on how much you can contribute across all IRAs (traditional and Roth combined). For 2024, that limit is $7,000 if you are under 50, or $8,000 if you are 50 or older. These limits change each year.

Do not invest the money yet. Leave it in cash or a money market fund. This step should take a few days to settle.

At the end of the tax year, file Form 8606 with your tax return. On this form, you report the contribution as a non-deductible contribution. You get no tax deduction for this money — that is the whole point. If you do not file Form 8606, the IRS will assume your contribution was deductible, and you will owe tax on the money twice: once when you convert it, and again when you withdraw it in retirement.

Step 2: Convert the traditional IRA to a Roth IRA

After the contribution has settled (usually a few days), log into your brokerage account and initiate a conversion. Most brokerages have a "convert to Roth" button or option in the IRA section. You select the traditional IRA account, choose how much to convert (usually all of it), and confirm. The brokerage will move the money from the traditional IRA to a Roth IRA in your name.

The conversion can happen in the same calendar year as the contribution, or in the following year — but it must happen before you file your tax return for the year of the contribution. If you contribute in December 2024, you can convert anytime through April 15, 2025 (or October 15, 2025 if you file an extension).

The brokerage will send you a Form 1099-R showing the conversion. Keep this document — you will need it to file your taxes.

Understanding the pro-rata rule and its tax consequences

The pro-rata rule is the reason a backdoor Roth can become expensive. Here is how it works: if you have any balance in a traditional IRA, SEP IRA, or straightforward IRA on December 31 of the year you convert, the IRS treats all your IRAs as one pool for tax purposes. The conversion is then taxed based on the ratio of pre-tax money to after-tax money in that entire pool.

Example: You have a traditional IRA with $50,000 in it (from an old 401(k) rollover). You contribute $7,000 to a new traditional IRA and when ready convert it. The pro-rata rule says your conversion is 50,000 / 57,000 = 88% pre-tax money. So 88% of your $7,000 conversion ($6,160) is taxable income in the year you convert. You owe income tax on $6,160, even though you only converted $7,000.

To avoid this, you must have zero balance in all traditional, SEP, and straightforward IRAs on December 31 of the conversion year. If you have an old 401(k) or 403(b) from a previous job, the pro-rata rule does not explore to it — only to IRAs. Some people roll old 401(k) balances into their current employer's 401(k) plan specifically to avoid the pro-rata rule before doing a backdoor Roth.

Reporting the conversion on your tax return

You report a backdoor Roth on Form 8606, Part II. You will need the Form 1099-R from your brokerage, which shows the gross amount converted. On Form 8606, you also report the basis of the conversion — the amount of non-deductible contributions you made.

If the entire conversion is non-deductible contributions (meaning no pro-rata rule applied), your taxable income from the conversion is zero. The money moves to the Roth tax-free. If the pro-rata rule applied, you calculate what portion of the conversion is taxable and report that as income.

Form 8606 is filed with your Form 1040. If you do not file it, the IRS will not know you reported the contribution as non-deductible, and you will face double taxation when you withdraw the money in retirement.

Timing: when to contribute and when to convert

You can contribute to a traditional IRA anytime during the tax year or up to the filing important date of the following year. For the 2024 tax year, you can contribute through April 15, 2025. You can convert anytime after the contribution settles, but the conversion must also be completed by April 15, 2025 to be reported on your 2024 taxes.

Many people contribute in early January and convert a few days later, once the contribution has cleared. This minimizes the time the money sits in a traditional IRA earning gains (which would be taxable if converted). Others contribute at the end of the year and convert in January of the following year.

If you miss the April 15 important date, you can still do the conversion, but it will be reported on the following year's taxes. This does not disqualify the conversion — it just shifts when you pay the tax.

What happens after the conversion

Once the money is in the Roth IRA, it grows tax-free. You can withdraw contributions anytime without penalty or tax. You can withdraw earnings penalty-free after age 59½, provided the Roth has been open for at least five tax years. If you withdraw earnings before age 59½, you owe income tax on the earnings plus a 10% penalty, unless an exception applies (disability, death, first-time home purchase up to $10,000 lifetime, or a few others).

The five-year rule is per Roth account, not per conversion. If you open your first Roth IRA in 2024 and do a backdoor Roth conversion, the five-year clock starts in 2024. Any backdoor Roth conversions you do in 2025, 2026, or later use the same five-year clock.

Common mistakes to avoid

The most common mistake is not filing Form 8606. If you contribute $7,000 non-deductibly and do not report it, the IRS assumes it was deductible. When you convert, you owe tax on the full $7,000. When you withdraw in retirement, you owe tax again. File Form 8606 every year you make a non-deductible contribution, even if you convert when ready.

The second mistake is not checking for other IRA balances before converting. If you have a rollover IRA from an old 401(k), a SEP IRA from self-employment income, or a straightforward IRA from a previous employer, the pro-rata rule will explore. Consolidate or roll these into a 401(k) if possible before you convert.

A third mistake is converting too much. You are not required to convert the entire $7,000 contribution. If you have other IRA balances and want to avoid the pro-rata rule, you can contribute $7,000 and convert only part of it, leaving the rest to grow in the traditional IRA. This is less common but is an option.

Frequently Asked Questions

Can I do a backdoor Roth if I have a 401(k) at work?

Yes. The pro-rata rule applies only to IRAs, not to 401(k)s, 403(b)s, or other employer plans. If your only IRA is the one you are converting, you have no pro-rata problem. If you have a separate rollover IRA or inherited IRA, those count toward the pro-rata calculation.

What if I convert and then the market drops before I file my taxes?

You can undo the conversion by filing Form 8606 and reporting a recharacterization, but only if your brokerage allows it and you do so before the tax filing important date. This is rare and complicated — most brokerages no longer allow recharacterizations. If you convert $7,000 and it drops to $5,000, you still owe tax on the full $7,000 you converted. The loss does not offset the conversion tax.

Do I have to do the conversion in the same year as the contribution?

No. You can contribute in December 2024 and convert in January 2025 or later. Both must be reported on your 2024 tax return if you convert by April 15, 2025. If you convert after April 15, 2025, it is reported on your 2025 taxes instead.

What if my employer offers a Roth 401(k) — can I do a backdoor Roth instead?

You can do both, but they serve different purposes. A Roth 401(k) has higher contribution limits ($23,500 in 2024 for those under 50) and no income limits. A backdoor Roth lets you contribute $7,000 regardless of income. Some people max out the Roth 401(k) first, then do a backdoor Roth with additional savings.

Can my spouse do a backdoor Roth if I do one?

Yes, each spouse has their own $7,000 contribution limit and can do a separate backdoor Roth. The pro-rata rule is calculated separately for each person based on their own IRA balances.