A backdoor Roth IRA moves after-tax IRA money into a Roth

A backdoor Roth IRA is a two-step strategy, not a separate kind of account: make a nondeductible, after-tax contribution to a traditional IRA, then convert that money to a Roth IRA. It is most relevant for people above the income limits for direct Roth contributions, because Roth conversions do not have the same income limit. The catch for an everyday investor is that pre-tax money in other IRAs can make much of the conversion taxable.

The strategy does not erase the annual IRA contribution limit or the earned-income requirement for a contribution. It changes the route money takes into a Roth account.

How a backdoor Roth IRA works

1. Make a nondeductible traditional IRA contribution. “Nondeductible” means you do not claim an upfront tax deduction for that contribution. It creates after-tax basis, meaning money on which tax has already been paid.
2. Convert funds to a Roth IRA. A conversion moves traditional IRA assets into a Roth IRA. Unlike a direct Roth contribution, a conversion has no income or age requirement.
3. Report the transaction. The nondeductible contribution and conversion need to be reflected on the tax return. Form 8606 tracks nondeductible IRA contributions and helps establish the after-tax basis used in calculating the conversion’s taxable share.

Direct Roth IRA eligibility phases out at specified modified adjusted gross income, or MAGI, levels. A traditional IRA contribution can be nondeductible when a person cannot make a direct Roth contribution, and the subsequent conversion is not subject to the direct-contribution income test.

Once assets are in a Roth IRA, their potential growth can be tax-free, and qualified withdrawals are generally tax-free. Roth IRAs also do not require lifetime required minimum distributions, or RMDs. Qualified treatment for earnings depends on applicable age and five-tax-year requirements, so a conversion does not make every future withdrawal automatically tax-free.

The backdoor Roth IRA question to answer first: do you have other IRAs?

Before focusing on the new contribution, inventory all non-Roth IRA money. The aggregation approach described by brokerage firms looks across traditional IRA balances when determining the taxable portion of a conversion. That means opening a fresh, empty traditional IRA does not isolate the new after-tax contribution for this calculation.

The relevant pool generally includes traditional, SEP and SIMPLE IRAs. It does not include Roth IRAs or inherited IRAs. Within the combined pool, deductible contributions and investment earnings are pre-tax money; nondeductible contributions are after-tax basis. A conversion is treated as containing each category in proportion to its share of the combined IRA balance. This is commonly called the pro-rata rule.

Illustrative pro-rata calculation

Hypothetical inputs: Your combined traditional IRA balance is $50,000. Of that total, $5,000 is nondeductible basis and $45,000 is deductible contributions and earnings. You convert $5,000 to a Roth IRA.

• After-tax share: $5,000 ÷ $50,000 = 10%
• Pre-tax share: $45,000 ÷ $50,000 = 90%
• Taxable portion of the $5,000 conversion: $5,000 × 90% = $4,500
• Non-taxable return of basis: $5,000 × 10% = $500

In this example, converting the amount of the recent contribution does not mean that only the new after-tax money was converted. The calculation is driven by the combined balance and its mix of pre-tax money and basis.

Other tax details that can change the result

Investment gains before conversion: If the contribution earns interest or investment gains while in the traditional IRA, that growth is generally taxable when converted.

Tax rate and location: Deductible traditional IRA contributions and earnings included in a conversion are generally taxable as ordinary income. State and potentially local tax treatment can also matter alongside federal tax.

Conversion withdrawal clock: Roth rules include five-year provisions. For people under age 59½, each conversion can have its own five-year period before converted principal is penalty-free, subject to exceptions. The five-tax-year rule for qualified withdrawal of Roth earnings is a separate concept.

A backdoor Roth is also different from a standard Roth conversion, which moves deductible traditional IRA contributions to Roth and is fully taxable in the year of conversion. It is separate from a “mega-backdoor Roth,” a workplace-plan strategy that requires a 401(k) with Roth and after-tax features.

A practical screening checklist

• Confirm whether direct Roth IRA income limits, rather than the annual IRA contribution limit, are the reason you are considering the strategy.
• List balances in every traditional, SEP and SIMPLE IRA, and identify documented nondeductible basis versus pre-tax amounts.
• Estimate whether the pro-rata calculation would make the conversion substantially taxable.
• Keep confirmation of the contribution and conversion, plus prior Form 8606 filings.
• Account for taxable gains and possible federal, state and local tax effects before treating a conversion as tax-free.
• Get tax-professional guidance on the reporting, timing and tax consequences for your circumstances.

For the underlying account trade-offs, see our comparison of Roth and traditional IRAs.

Frequently asked questions

How does the pro-rata rule affect a backdoor Roth IRA?

The pro-rata rule generally treats all of your traditional IRA balances as one pool when calculating the taxable part of a conversion. If that pool contains pre-tax contributions or earnings, the conversion is treated as partly pre-tax and partly after-tax in the same proportion. SEP and SIMPLE IRAs are also included in the aggregation described by the sources.

Do you pay taxes on a backdoor Roth IRA?

A nondeductible contribution is after-tax money, so it generally is not taxed again on conversion. But investment gains before conversion, plus the share of a conversion attributed to pre-tax IRA money under the pro-rata rule, are generally taxable as ordinary income. State and local taxes may also apply.

What tax form is needed for a backdoor Roth IRA?

Brokerage sources say Form 8606 is used to track nondeductible traditional IRA contributions and report the conversion-related basis calculation. Keeping records of contributions, conversions and earlier Form 8606 filings helps document that after-tax money was not taxed twice.

Is a backdoor Roth IRA the same as a mega-backdoor Roth?

No. A backdoor Roth IRA uses a nondeductible traditional IRA contribution followed by a Roth IRA conversion. A mega-backdoor Roth is a separate workplace-plan approach that requires a 401(k) with after-tax contribution and Roth features.

Sources

• Backdoor Roth IRA: What it is and how to set it up - Vanguard — investor.vanguard.com
• Backdoor Roth IRA: Is it right for you? — www.fidelity.com
• "Backdoor" Roth IRA — bcsb.com
• Backdoor Roth IRA: Advantages and Tax Implications ... — www.investopedia.com
• What is a Backdoor Roth IRA? Income Limits, Taxes, & Rules — www.schwab.com