Backdoor Roth IRA Explained: How It Works and Who Should Use It

What a "backdoor Roth" actually is

A backdoor Roth IRA is not a special account type. You will not find it on any brokerage application form. It is a nickname for a two-step manoeuvre that gets money into a Roth IRA when your income is too high to contribute directly.

The rules create the situation. Direct Roth IRA contributions phase out above certain income levels. For the 2025 tax year, the phase-out range runs roughly from $150,000 to $165,000 of modified adjusted gross income for single filers, and roughly $236,000 to $246,000 for married couples filing jointly. Above the top of the range, you cannot contribute directly at all. (Those thresholds are indexed and move most years, and the 2026 figures are already higher, so always check the current IRS numbers rather than relying on a figure you read once.)

But there is no income limit on contributing to a traditional IRA, and there is no income limit on converting a traditional IRA to a Roth. Put those two facts together and you have the backdoor.

How it works, step by step

The mechanics are genuinely simple. The complications come later.

Step one: contribute to a traditional IRA. For 2025 the IRA contribution limit is $7,000, or $8,000 if you are 50 or older. Because your income is high, this contribution will almost certainly be non-deductible, meaning you get no tax break for making it. That is the point. You are creating after-tax money inside a traditional IRA.

Step two: convert it to a Roth IRA. You tell your custodian to convert the traditional IRA balance into a Roth IRA. Most brokerages let you do this online in a few clicks.

Step three: report it properly. The contribution and the conversion both go on Form 8606. This form is what tells the IRS that the money you converted was already taxed once, so it should not be taxed again. Skip it, or fill it in badly, and you can end up paying tax twice on the same dollars.

Step four: invest the money. A surprising number of people complete the conversion and then leave the cash sitting in a money market fund for years.

If the traditional IRA contained nothing but your fresh non-deductible contribution, and it earned a few dollars of interest before you converted, the tax owed on the conversion is close to zero. You pay tax only on the growth between contribution and conversion.

The pro-rata rule is the thing that ruins it

Here is where most people get hurt.

The IRS does not look at your traditional IRA in isolation. When you convert, it aggregates the balances of all your traditional, SEP and SIMPLE IRAs as of 31 December of that year, and works out what proportion of the total is after-tax money. That proportion is the only part of your conversion that comes out tax free. The rest is taxable income.

So if you have a $93,000 rollover IRA sitting there from an old employer plan, all of it pre-tax, and you add a $7,000 non-deductible contribution and convert that $7,000, only 7 percent of the conversion is tax free. The other 93 percent gets added to your income at your marginal rate. You have not done anything illegal, but you have created a tax bill you probably did not budget for, and you have left a mess of basis to track for years afterwards.

There are ways around this, most commonly rolling pre-tax IRA money into a current employer's 401(k) if the plan accepts incoming rollovers, which removes it from the pro-rata calculation. Whether that is sensible depends on the plan's costs and fund choices, and the timing has to be right because the calculation is done at year end, not on the day you convert.

Can you contribute before you have actually earned the income?

Yes, with one condition that catches people out.

You can fund an IRA for a given tax year at any point from 1 January of that year right up to the tax filing deadline the following April. You do not have to have earned the money yet. Someone contributing the full amount on 2 January is contributing against income they have not been paid.

The condition is that by the end of the tax year, you must have at least that much taxable compensation, broadly earned income from work or self-employment. Investment income, rental income, pension income and most Social Security do not count. If you contribute $7,000 in January and then only earn $4,000 all year, $3,000 of that contribution becomes an excess contribution, and excess contributions attract a 6 percent penalty for every year they stay in the account.

Two things soften this. Spouses filing jointly can use a spousal IRA, where one partner's earnings support a contribution for the other, subject to the couple's total compensation. And an excess contribution can usually be fixed without penalty if you withdraw it, along with the attributable earnings, before the filing deadline. But that fix is fiddly, and if you have already converted the money to a Roth it becomes considerably more fiddly.

Contributing early is generally good, because the money starts compounding sooner. Just be reasonably confident about the income.

Does the 529-to-Roth rollover have income limits?

No, and this is one of the more genuinely useful quirks in the rules.

Since 2024, leftover money in a 529 education account can be rolled into a Roth IRA in the beneficiary's name. The income phase-out that blocks high earners from direct Roth contributions does not apply to these rollovers. A beneficiary earning far above the threshold can still receive one.

That said, the conditions are tight:

• The 529 must have been open for at least 15 years.
• Contributions made in the previous 5 years, and their earnings, are not eligible to move.
• There is a $35,000 lifetime cap per beneficiary.
• Each year's rollover counts against that year's IRA contribution limit, so you cannot move $35,000 in one go, and it reduces what the beneficiary can contribute separately.
• The beneficiary must have earned income at least equal to the amount rolled over in that year.

So the earned income test still bites, even though the MAGI test does not. A recent graduate with a full-time job can typically use it. A beneficiary with no job that year cannot.

Some states have not conformed to the federal treatment, which can create a state tax charge, and several details are still awaiting clearer IRS guidance.

Who should use a backdoor Roth, and who should not

It suits someone earning above the direct contribution limit, with little or no pre-tax money in traditional, SEP or SIMPLE IRAs, who is comfortable filing Form 8606 correctly each year.

It is often a poor fit for someone with a large pre-tax IRA balance they cannot move, someone who might need the money back within five years, or someone whose income is close enough to the phase-out that a direct partial contribution would do the job with less paperwork. Self-employed people with SEP IRAs need to think especially carefully, because that SEP balance sits right in the pro-rata calculation.

There is also the ongoing question of legislative risk. Proposals to close the backdoor have surfaced repeatedly and none has passed, but the strategy exists because of a gap in the rules rather than a deliberate policy choice.

If you want the worked numbers, including a full pro-rata example, the five-year clock rules that apply separately to conversions, the Form 8606 walkthrough and a year-by-year checklist for keeping it clean, that is what The Roth IRA Rules That Trip People Up (£19) is for.

This article is general education, not personalised tax or investment advice. Rules and figures change, so check current IRS guidance or speak to a qualified professional about your own situation.