Reporting a Roth IRA Conversion on Your Tax Return

Converting funds from a traditional IRA to a Roth IRA requires reporting on Form 8606, which tracks the conversion amount, calculates any taxable portion, and feeds that tax liability into your Form 1040. The process is straightforward if you have no other traditional IRAs, but becomes complex if you hold multiple IRAs or have existing after-tax basis.

Form 8606 and the calculation of taxable conversion income

Form 8606 is the IRS form that quantifies your Roth conversion for tax purposes. It has separate sections for:

1. Traditional, SEP, or SIMPLE IRA distributions.
2. Conversions and recharacterizations.
3. Nonqualified Roth IRA distributions (covered separately).

For a conversion, you fill in:

• The balance of all your traditional IRAs (including SEP and SIMPLE IRAs) as of December 31 of the conversion year.
• The amount you converted to Roth.
• Your after-tax basis (if any) in those traditional IRAs.

The form then applies the pro-rata rule, which requires you to account for all traditional-IRA balances and after-tax contributions when calculating the taxable portion of a conversion. This is a critical step that trips up many filers.

The pro-rata rule and why it matters

The pro-rata rule states that when you convert a portion of your traditional-IRA assets to Roth, the conversion is treated as a proportional draw from both pre-tax and after-tax funds in all of your traditional IRAs combined.

Example: You have two traditional IRAs.

• IRA A: $40,000 (all pre-tax, from a rollover).
• IRA B: $10,000 (all after-tax contributions).
• Total traditional IRA balance: $50,000
• After-tax basis: $10,000
• Pre-tax balance: $40,000

You convert $20,000 from IRA A to Roth. What portion is taxable?

The pro-rata rule says: $20,000 × ($40,000 ÷ $50,000) = $16,000 is pre-tax and thus taxable. The remaining $4,000 ($20,000 × ($10,000 ÷ $50,000)) is after-tax basis and is not taxable.

Your taxable income from the conversion: $16,000.

This is why filers are caught off guard. You cannot convert just the after-tax portion and avoid the tax bill. The entire balance of all traditional IRAs is considered, and the tax is proportional.

Form 8606 section by section

Part I: Traditional, SEP, and SIMPLE IRA Distributions

This section applies if you took any distributions from traditional IRAs during the year, whether or not you converted.

Lines 1–2: Report the value of all your traditional IRAs as of December 31 of the conversion year (beginning of the following year). Include:

• Traditional IRAs held for yourself.
• SEP IRAs.
• SIMPLE IRAs.
• Do not include Roth IRAs, 401(k)s, or other employer plans.

Lines 3–4: Report any distributions you took from traditional IRAs during the year (not conversions; actual withdrawals of cash or assets for your use).

Line 5: Your after-tax contributions (basis) in traditional IRAs. This is the cumulative total of non-deductible contributions you made over time. You should receive a Form 8606 from prior years showing your basis; add any new after-tax contributions made during the current year.

Line 6: The form calculates the nontaxable portion of your distribution, if any. This is Line 5 × (Line 4 ÷ Line 1)—your basis, multiplied by the ratio of your distribution to your total IRA balance.

Line 7: Your taxable distribution is the total distribution (Line 4) minus the nontaxable portion (Line 6).

Part II: Conversions and Recharacterizations

This section is where a Roth conversion is reported.

Line 8: The amount converted (or recharacterized) from traditional to Roth. This is the full amount of assets moved, not just the taxable portion.

Lines 9–10: The form recalculates the nontaxable and taxable portions using the same pro-rata logic. Your basis (Line 9) is multiplied by the ratio of the conversion amount to your total traditional-IRA balance. This gives the nontaxable conversion amount.

Line 11: The taxable portion of the conversion. This is the conversion amount (Line 8) minus the nontaxable portion (Line 9).

This is the figure that flows to your Form 1040 as ordinary income.

Entering the taxable conversion on Form 1040

Once you have calculated the taxable portion on Form 8606, you report it on Form 1040 under traditional IRA distributions:

• Form 1040, line 4a: Total distribution from traditional IRAs, including the conversion amount.
• Form 1040, line 4b: The taxable portion (from Form 8606, line 11).
• Schedule 1 (Form 1040), line 4: If required, report the distribution separately.

The taxable portion is added to your ordinary income for the year and taxed at your marginal tax rate (whatever bracket your total income lands you in—10%, 12%, 22%, 24%, etc.).

Standard deduction and tax brackets

A large conversion can push you into a higher tax bracket or reduce or eliminate your standard deduction. For example, if you are single, have modest income, and take a $50,000 conversion that is 100% taxable, your income rises by $50,000. This may bump you from the 12% bracket into the 22% or 24% bracket, or eliminate income-based credits you would otherwise claim.

Tax planning for conversions often focuses on choosing a year with lower income (a gap year between jobs, before Social Security starts, during a down market when taking a conversion makes sense financially) to minimize the tax hit.

Special case: backdoor Roth conversions

A backdoor Roth conversion is a two-step process: you contribute after-tax funds to a traditional IRA, then immediately convert that amount to Roth. The goal is to bypass income limits on direct Roth contributions.

Form 8606 must still be filed. You report:

• The after-tax contribution as new basis (on the line for non-deductible contributions).
• The conversion amount.
• The pro-rata calculation (which, in a pure backdoor Roth with no other IRA balances, usually results in zero taxable income because all funds are after-tax basis).

However, if you have any other traditional-IRA balance (a rollover from an old 401(k), inherited IRA, etc.), the pro-rata rule applies, and the conversion becomes partially taxable. This is the hidden trap of the backdoor Roth.

Interaction with other retirement accounts

Form 8606 applies only to traditional, SEP, and SIMPLE IRAs. It does not include:

• 401(k)s, 403(b)s, or 457 plans.
• Roth 401(k)s or Roth 403(b)s (these are reported separately).

If you convert a traditional 401(k) to a Roth 401(k) (an in-service conversion), you do not use Form 8606. Instead, the conversion is reported on Form 1099-R and rolled directly to Form 1040 as a distribution. However, the same taxability logic applies: the pre-tax portion of the converted amount is ordinary income.

Amended returns and correcting conversions

If you file your return and later discover you made an error in your conversion reporting (miscalculated basis, missed a traditional-IRA balance, overstated the conversion amount), you can file an amended Form 1040 and Form 8606 using Form 1040-X.

If you filed a conversion but want to undo it (a “recharacterization”), the rules changed significantly in 2018. As of now, recharacterizations are no longer permitted; once you convert, the conversion is final. You cannot take it back. The only option is to treat the conversion as a non-qualifying distribution and potentially pay a penalty and tax to correct it, which is complex and usually not worth the effort.

State tax implications

Form 8606 is a federal tax form. State taxation of conversions varies:

• States with no income tax (Florida, Texas, etc.): No state tax on the conversion.
• States with income tax: Most treat conversions the same way as the federal government—the taxable portion is state income.
• A few states may apply different rules, so check your state’s department of revenue or a tax professional.

Common mistakes and red flags

1. Forgetting the pro-rata rule: Filing a conversion without accounting for all traditional-IRA balances is the most common error. The IRS catches this in matching Form 8606 to custodian reports.

2. Misreporting basis: If you have been making non-deductible contributions for years but do not have a Form 8606 on file, you must reconstruct your cumulative basis. Missing this inflates your taxable conversion.

3. Not filing Form 8606: Even if you think the entire conversion is non-taxable, you must file Form 8606 to establish basis for the Roth account. Failing to do so can trigger issues on future non-qualified distributions.

4. Treating a conversion as a withdrawal: Some filers mistakenly report the conversion as a distribution to themselves (Box 1 on Form 1099-R) rather than as a conversion (Box 2 or code 02). This triggers early-withdrawal penalties if applicable.

See also