Understanding Form 8606

What Is Form 8606?

Form 8606 is the form that tracks your non-deductible IRA contributions over time. It is filed with your tax return in any year you make a non-deductible contribution to a traditional IRA, convert traditional IRA money to a Roth, or take a distribution from a traditional IRA that contains non-deductible contributions. It is also filed when you take certain Roth IRA distributions.

The form has three parts, each covering a different transaction type, but they all connect to the same underlying concept: basis. Your basis is the money you already paid tax on. Without Form 8606, the IRS has no record that any of your IRA money was already taxed, and they will tax it again on the way out.

When Do You File It?

Form 8606 is filed with your federal tax return (Form 1040) in any year one of the following applies:

• You made a non-deductible contribution to a traditional IRA.
• You converted any amount from a traditional IRA to a Roth IRA.
• You received a distribution from a traditional IRA and you have basis (non-deductible contributions) in any of your traditional IRAs.
• You received a distribution from a Roth IRA.

The form is due when your tax return is due, including extensions. If you did not file it and should have, you can file it late. The IRS assesses a $50 penalty for failure to file Form 8606, but the real cost of not filing is much higher than $50. It is the loss of your basis record, which can mean paying tax twice on the same money.

Why Basis Matters

When you contribute to a traditional IRA and do not take a tax deduction (because your income was too high or you chose not to), that contribution is called a non-deductible contribution. You already paid income tax on that money. It went into the IRA with after-tax dollars. That amount is your basis.

When you eventually take a distribution or do a Roth conversion, the basis portion comes out tax-free because you already paid tax on it. Without Form 8606, the IRS does not know that any of your IRA money is after-tax. They treat the entire account as pre-tax and tax the full distribution.

Filing Form 8606 is how you avoid paying tax twice on the same dollar.

Part I: Non-Deductible Contributions

Part I tracks your cumulative non-deductible IRA basis.

• Line 1 is your current year non-deductible contribution.
• Line 2 is your total basis from all prior years (carried forward from Line 14 of last year's Form 8606).
• Line 3 is the total.
• Lines 6 through 14 calculate the tax-free and taxable portions of any distributions or conversions you made during the year, using the pro-rata formula.

Line 14 is the critical number: your remaining basis after the current year's transactions. This number carries forward to next year's Form 8606. If you lose track of Line 14, you lose track of your basis.

Part II: Roth Conversions

Part II reports the taxable amount of a Roth conversion. If you converted traditional IRA money to a Roth, the taxable amount depends on how much basis you had at the time of conversion.

The pro-rata rule applies. You cannot cherry-pick only the non-deductible (basis) dollars for the conversion. The IRS looks at all your traditional IRA money across every account and calculates a single tax-free percentage.

Part II takes the conversion amount from Line 16, applies the tax-free fraction from Part I, and calculates the taxable portion on Line 18. This is the number that goes on your tax return as income.

Part III: Distributions from Roth IRAs

Part III applies to Roth IRA distributions. Most qualified Roth distributions (after age 59½ and the 5-year rule) are tax-free and do not need to be reported here.

Part III is used when a Roth distribution does not meet the qualified criteria and the ordering rules need to be applied to determine whether any portion is taxable or subject to the 10% early withdrawal penalty.

The Roth ordering rules distribute money in a specific sequence:

• Contributions first (always tax-free and penalty-free).
• Conversions next (tax-free but potentially subject to the 5-year conversion clock for penalty purposes).
• Earnings last (taxable and potentially subject to penalty if the distribution is not qualified).

The Pro-Rata Connection

Form 8606 is where the pro-rata rule lives on paper. Lines 6 through 13 perform the calculation that determines what percentage of your distribution or conversion is tax-free based on your total basis divided by the total value of all your traditional, SEP, and SIMPLE IRAs as of December 31.

This is why the December 31 fair market value on Form 5498 Box 5 matters. It feeds directly into the Form 8606 pro-rata calculation.

If you have $50,000 in basis and $500,000 in total IRA value, 10% of any distribution or conversion is tax-free. The other 90% is taxable. You cannot convert just the $50,000 in basis and call it tax-free. The IRS forces proportional treatment across the entire pool.

What Happens When You Don't File It

The $50 penalty for not filing Form 8606 is almost irrelevant. The real cost is losing your basis.

If you made non-deductible contributions for 10 years and never filed Form 8606, the IRS has no record that any of your IRA money is after-tax. When you take distributions in retirement, the IRS taxes the full amount. You pay tax on money you already paid tax on.

Depending on the size of your non-deductible contributions and the value of your account, the double taxation can cost thousands of dollars over a retirement. The form exists to prevent that. Skipping it does not save you paperwork. It costs you money.

How to Reconstruct Lost Basis

If you made non-deductible contributions and did not file Form 8606 in prior years, you can reconstruct your basis.

1. Gather your tax returns from the years you contributed.
2. Look for Form 5498 showing IRA contributions in years your income exceeded the deductibility limits.
3. Contact your custodian for historical contribution records.
4. Once you have the total amount of non-deductible contributions, file a Form 8606 for the current year showing the cumulative basis on Line 2.
5. You can also file late Forms 8606 for prior years.

The reconstruction process is tedious but the alternative is paying tax on money that should come out tax-free.

Frequently Asked Questions