Traditional IRA After-Tax Contributions: Form 8606 and Pro-Rata Rule

After-tax contributions to a Traditional IRA are deposits of money you have already paid income tax on, made when your income is too high to claim the usual deduction. You can still put the money in, up to the standard annual limit, but the undeducted amount becomes your “basis” in the account. Tracking that basis on Form 8606 every year is what keeps the IRS from taxing the same dollars a second time when you eventually withdraw them.

For 2026, the contribution ceiling is $7,500, or $8,600 if you are 50 or older, and that cap covers your combined deposits across every Traditional and Roth IRA you own.¹ You need earned income (wages, salary, commissions, or self-employment income) to contribute, and you have until your tax filing deadline the following April to make a contribution for the prior year.²

When Your Contribution Becomes Non-Deductible

Two things determine whether you can deduct a Traditional IRA contribution: whether you or your spouse is covered by an employer retirement plan, and your modified adjusted gross income. If neither spouse has workplace plan coverage, the full contribution is deductible at any income level.³ The phase-outs only bite once employer coverage enters the picture.

For 2026, the deduction phases out over these MAGI ranges:¹

Single or head of household, covered by a workplace plan: $81,000 to $91,000.
Married filing jointly, contributing spouse covered: $129,000 to $149,000.
Married filing jointly, contributing spouse not covered but the other is: $242,000 to $252,000.
Married filing separately, covered by a workplace plan: $0 to $10,000.

Above the top of your range, the entire contribution is non-deductible. Inside the range, part is deductible and part is not. The married-filing-separately band is a common trap: with only $10,000 of room, almost any earned income wipes the deduction out.

Non-deductible does not mean prohibited. You put the same dollars in and take the same investment exposure. What changes is that the contribution goes in after tax, so you have basis in the account that needs to be documented.

Reporting the Contribution on Form 8606

Every non-deductible contribution must be reported on IRS Form 8606, Nondeductible IRAs, filed with your annual tax return for the year of the contribution, even if you would not otherwise need to file a return.² The form records this year’s after-tax contribution and carries forward the cumulative basis from all prior years, so a completed 8606 is a running ledger of every after-tax dollar you have ever put in.⁴

Skipping the form carries a $50 penalty per missed year, and overstating your non-deductible contributions triggers a separate $100 penalty.⁵ The fines themselves are small. The real damage is what happens years later: without Form 8606 on record, the IRS treats every dollar in your Traditional IRA as pre-tax, and every distribution is fully taxable, including money you already paid tax on before contributing.²

If you missed the form in prior years, you can file a corrected 8606 with an amended return (Form 1040-X) for each affected year.⁶ The IRS instructions say to hold onto your 8606s and supporting records until every IRA distribution is complete.⁴ For most people that is decades. Reconstructing 20 or 30 years of basis from scratch is not something you want to attempt.

How Withdrawals Get Taxed: The Pro-Rata Rule

Once a Traditional IRA holds both pre-tax and after-tax money, you cannot choose which dollars come out first. The IRS applies the pro-rata rule: every distribution is treated as a proportional mix of taxable and non-taxable funds.⁷

The formula divides your total basis by the sum of your year-end IRA balance plus any distributions taken during the year. That fraction is the tax-free percentage. Every Traditional, SEP, and SIMPLE IRA you own is combined for this calculation. You cannot segregate the after-tax dollars in a single account and pull them out cleanly.⁸

Say you have a $95,000 year-end balance across your non-Roth IRAs and $10,000 of documented basis. During the year you took a $5,000 distribution. The denominator is $95,000 plus $5,000, which is $100,000. Your non-taxable fraction is $10,000 divided by $100,000, or 10%. Of the $5,000 distribution, $500 is a tax-free return of basis and $4,500 is ordinary income.⁷ Your remaining basis drops to $9,500 and carries forward on next year’s Form 8606.

Required minimum distributions follow the same math. Each mandatory withdrawal is partly taxable and partly a return of basis, spread proportionally over the years.⁹ You never get to exhaust the basis first.

Using After-Tax Contributions for a Backdoor Roth

The most common reason to make a non-deductible Traditional IRA contribution on purpose is the “backdoor Roth.” Direct Roth contributions phase out at $168,000 (single) or $252,000 (married filing jointly) of MAGI for 2026.¹ Conversions from a Traditional IRA to a Roth have no income restriction.

The strategy has two steps. Contribute to a Traditional IRA on a non-deductible basis and report it on Form 8606.¹⁰ Then convert the balance to a Roth. If the Traditional IRA held nothing but the fresh after-tax contribution, the conversion is essentially tax-free, because you are moving after-tax basis from one bucket into another.

The catch is the pro-rata rule, which applies to conversions the same way it applies to withdrawals.¹¹ If you have any pre-tax money in any Traditional, SEP, or SIMPLE IRA, part of every conversion is taxable. With a $93,000 pre-tax balance and a $7,500 non-deductible contribution, your total is $100,500, and only about 7.5% of the conversion comes out tax-free. The rest generates a tax bill.

One workaround is rolling existing pre-tax IRA balances into your current employer’s 401(k) or 403(b) before converting, if the plan accepts incoming rollovers. Money inside an employer plan is not part of the IRA aggregation pool. Self-employed savers can use a solo 401(k) the same way. Order matters: move the pre-tax dollars out first, then make the non-deductible contribution and convert. The IRS measures your non-Roth IRA balances as of December 31, so doing it backwards still triggers pro-rata for the conversion year.⁷

Fixing an Excess Contribution

Contributing more than the combined annual limit across your IRAs triggers a 6% excise tax on the excess for every year it stays in the account.¹² To avoid the penalty, withdraw the excess and any earnings it generated by your tax filing deadline, including extensions.¹³ The earnings are taxable in the year of the excess contribution, and if you are under 59½, the earnings portion can also draw a 10% early withdrawal penalty.

Miss that deadline and the 6% tax applies every year until you fix it, either by withdrawing the excess or by contributing less in a later year so the excess absorbs into the new year’s room. The penalty is capped at 6% of your combined IRA value at year-end, but compounding annually is still expensive.¹²

1
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
2
Internal Revenue Service. Publication 590-A (2025), Contributions to Individual Retirement Arrangements (IRAs)
3
Internal Revenue Service. IRA Deduction Limits
4
Internal Revenue Service. Instructions for Form 8606 (2025)
5
Office of the Law Revision Counsel. 26 U.S. Code 6693 – Failure to Provide Reports on Certain Tax-Favored Accounts or Annuities
6
Internal Revenue Service. Instructions for Form 8606 (2025)
7
Internal Revenue Service. Publication 590-B (2025), Distributions from Individual Retirement Arrangements (IRAs)
8
Internal Revenue Service. About Form 8606, Nondeductible IRAs
9
Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs
10
Internal Revenue Service. Form 8606 – Nondeductible IRAs
11
Internal Revenue Service. Rollovers of After-Tax Contributions in Retirement Plans
12
Internal Revenue Service. Retirement Topics – IRA Contribution Limits
13
Internal Revenue Service. IRA Year-End Reminders