A backdoor Roth IRA is a conversion strategy, not a new account

A backdoor Roth IRA is not a distinct account. It is a two-step retirement-saving strategy: make a nondeductible, after-tax contribution to a traditional IRA, then convert those assets to a Roth IRA. It is commonly considered by people whose income prevents a direct Roth IRA contribution, since Roth conversions do not have the same income restriction. The important catch is that the conversion may create a tax bill.

The mechanics are straightforward. The tax calculation can be less so, especially for people who already have traditional IRA money.

What a backdoor Roth IRA does

A Roth IRA is funded with money that has already been taxed. If applicable requirements are met, investment growth and withdrawals can receive tax-free treatment. Roth IRA owners also do not have required minimum distributions during their lifetimes, according to Vanguard and Fidelity.

Direct Roth IRA contributions are subject to income limits. A backdoor strategy uses a nondeductible traditional IRA contribution, meaning no upfront tax deduction is claimed, followed by a conversion into a Roth IRA. Vanguard, Fidelity, and Schwab describe Roth conversions as not subject to the income limits that apply to direct Roth contributions.

The basic sequence

1. Make an after-tax traditional IRA contribution. The contributor does not take a deduction for it. This after-tax amount is often called basis, meaning money that has already been taxed.
2. Convert traditional IRA assets to a Roth IRA. A conversion transfers the amount from the traditional IRA into the Roth IRA.
3. Report the transaction. Fidelity and Schwab say nondeductible IRA contributions are tracked using IRS Form 8606, and conversion reporting applies.

The rule that changes the math: pro rata treatment

The main complication is the pro rata rule. Fidelity says the IRA aggregation rule generally treats a taxpayer's traditional IRAs as one combined pool when calculating how much of a conversion is taxable. A person generally cannot designate only after-tax dollars in one IRA for conversion while ignoring pre-tax contributions and earnings held in other traditional IRAs. Fidelity's description excludes inherited IRAs and Roth IRAs from that grouping.

Worked example: a conversion can be mostly taxable

Hypothetical combined traditional IRA balance: $50,000. Assume $5,000, or 10%, represents nondeductible after-tax contributions. The remaining $45,000, or 90%, consists of deductible contributions and investment earnings.

Hypothetical conversion: $5,000. In Fidelity's example, the conversion carries the same 10% after-tax and 90% pre-tax mix as the combined IRA pool.

• After-tax portion: 10% of $5,000 = $500
• Taxable portion: 90% of $5,000 = $4,500

In this example, a new $5,000 after-tax contribution does not make the full $5,000 conversion tax-free. The existing pre-tax IRA balance changes the result. Fidelity says deductible contributions and investment earnings included in a conversion are generally taxable as ordinary income. Schwab also says growth that occurs between contribution and conversion may be taxable.

Potential Roth benefits, with withdrawal rules attached

Once assets are in a Roth IRA, the account offers potential tax-free growth and generally tax-free qualified withdrawals. Those outcomes depend on meeting the applicable rules, rather than on using the backdoor process itself. Fidelity says converted balances may be penalty-free if the five-year aging rule for each conversion is met or another exception applies. Qualified withdrawals of Roth IRA earnings have separate requirements.

A backdoor conversion can move money into a Roth account, but it does not erase tax on pre-tax IRA assets or override withdrawal rules.

A pre-conversion checklist

• List traditional IRA balances. Other traditional IRAs can affect the tax calculation.
• Separate basis from pre-tax money. Identify nondeductible contributions, deductible contributions, and earnings.
• Anticipate the taxable share. A conversion involving pre-tax contributions or earnings can produce ordinary income in the conversion year.
• Keep reporting in view. Nondeductible contributions are tracked on Form 8606.
• Check withdrawal rules. Converted assets can be subject to a five-year aging rule for penalty-free treatment.
• Get individualized tax help if needed. Fidelity recommends consulting a tax professional about timing, potential tax effects, and the conversion steps for a person's circumstances.

Frequently asked questions

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

The pro-rata rule generally treats all of your traditional IRAs as one pool when calculating the taxable share of a conversion. You generally cannot convert only after-tax contributions while setting aside pre-tax contributions and earnings in another traditional IRA. In Fidelity's example, a pool that is 90% pre-tax makes 90% of a $5,000 conversion, or $4,500, taxable.

Is a backdoor Roth IRA conversion taxable?

It can be. Nondeductible contributions generally have already been taxed, but deductible contributions and investment earnings included in a conversion are generally taxable as ordinary income, according to Fidelity. Schwab says growth between a traditional IRA contribution and conversion may also be taxable.

What tax form is used to report nondeductible IRA contributions?

Fidelity and Schwab say nondeductible IRA contributions are tracked on IRS Form 8606. That after-tax basis affects the tax calculation for a conversion.

How does a backdoor Roth IRA differ from a regular Roth conversion?

A backdoor Roth strategy starts with a nondeductible, after-tax traditional IRA contribution and then converts it to a Roth IRA. Fidelity describes a standard Roth conversion as a transfer of tax-deductible traditional IRA contributions to a Roth IRA, which would be fully taxable in the year of conversion. Traditional IRA aggregation and pro-rata treatment can affect conversion taxes.

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? - Fidelity Investments — www.fidelity.com
• What is a Backdoor Roth IRA? Income Limits, Taxes, & Rules — www.schwab.com