Inherited IRA After-Tax Basis: Recovering Non-Deductible Contributions Tax-Free

What Is IRA Basis?

Most traditional IRA contributions are deductible — you get a tax deduction when you contribute and pay taxes when you withdraw. But not always. If your income was too high to deduct your IRA contribution (or you didn't qualify for the deduction at all), you could still make a non-deductible contribution — contributing after-tax dollars to a traditional IRA.

Those after-tax dollars are your IRA basis. They were taxed when you earned them. When you take distributions later, the basis portion should come out tax-free — otherwise you pay taxes on the same dollars twice.

The IRS tracks basis through Form 8606. Every year a non-deductible contribution was made, the owner was supposed to file Form 8606 to declare it. The cumulative basis carries forward on line 14 from year to year. If the decedent filed consistently, you'll find the total basis on their last Form 8606.

What Happens to Basis When Someone Dies?

The basis doesn't disappear. Under IRC § 408(d)(2) and the IRS's published guidance in Publication 590-B, when an IRA with basis passes to a beneficiary, the basis passes too.¹ You — as the beneficiary — inherit both the account balance and the right to recover any unrecovered after-tax contributions tax-free.

This means that when you take distributions from the inherited IRA, a portion of each distribution should be treated as a nontaxable return of basis. The IRS will not automatically compute this for you. If you don't claim it on Form 8606, you'll be over-reporting taxable income.

The Critical Rule: Inherited Basis Stays Separate

Here's where most beneficiaries — and even many tax preparers — make a costly mistake. The inherited IRA basis cannot be combined with your own IRA basis for the pro-rata calculation.²

Normally, the IRS requires you to aggregate all your traditional, SEP, and SIMPLE IRAs when figuring how much of a distribution is taxable — this is the "pro-rata rule." But the inherited IRA is not yours. It's a separate pool. The math runs independently.

If you have basis in both your own traditional IRA and an inherited IRA, you must file two separate Forms 8606 — one for each pool — and calculate the taxable fraction of distributions independently for each. The IRS instructions for Form 8606 explicitly require this.²

How to Calculate the Taxable Portion of Distributions

The pro-rata formula for an inherited IRA distribution uses the balance and basis of only that inherited IRA. Here's the logic (simplified from the Form 8606 Part I worksheet):

1. Find the inherited IRA's total basis (from the decedent's last Form 8606, line 14).
2. Find the account balance at December 31 of the distribution year, plus any distributions taken during the year.
3. Calculate the nontaxable percentage: Basis ÷ (Year-end balance + Distributions)
4. Apply to the distribution: Nontaxable amount = Total distributions × Nontaxable percentage
5. The rest is taxable ordinary income.

Example: You inherit a $400,000 IRA. The decedent's last Form 8606 shows $40,000 of cumulative basis. You take a $50,000 distribution this year; the account is worth $360,000 at year-end.

• Denominator: $360,000 + $50,000 = $410,000
• Nontaxable percentage: $40,000 ÷ $410,000 = 9.76%
• Nontaxable portion of distribution: $50,000 × 9.76% = $4,878
• Taxable income: $50,000 − $4,878 = $45,122
• Remaining basis: $40,000 − $4,878 = $35,122 (carries forward)

You'd report $45,122 on your tax return instead of $50,000 — a meaningful difference at higher income brackets.

Form 8606 Filing Requirements for Beneficiaries

You must file Form 8606 in any year you take distributions from an inherited IRA that has basis. The key rules:

• File a separate Form 8606 for the inherited IRA — don't blend it with your own Part I calculation.
• On the inherited IRA's Form 8606, enter the decedent's name and SSN at the top (per IRS instructions).
• If you inherit IRAs from multiple different people, file one Form 8606 per decedent.
• The basis carries forward from year to year until it's fully recovered — typically over the 10-year SECURE window, or over your life expectancy if you're an eligible designated beneficiary (EDB) using the stretch.
• At the end of the 10-year window — when the final distribution depletes the account — any remaining basis comes out tax-free in that final year. Don't leave money on the table.

What If the Decedent Never Filed Form 8606?

This is common. The decedent may have made non-deductible IRA contributions but never filed Form 8606 — or filed it inconsistently. Without the records, you have no documented basis, and the IRS will treat 100% of every distribution as taxable.

You have a few options:

• Search the decedent's tax returns. Form 8606 is a standalone form filed with the annual return. If the decedent used a tax preparer, that preparer may have copies going back 7+ years.
• Request transcripts from the IRS. The IRS tax transcript (Form 4506-T) will show whether Form 8606 was filed, but generally only for the last 3 years.
• File a late Form 8606 for the years when non-deductible contributions were made. The IRS allows this, with a $50 penalty per missed year — far less than the tax cost of missing the basis entirely. If the contributions were made before records are available, reasonable reconstruction (bank records, brokerage statements showing IRA contributions) may support a defensible basis amount.
• Accept zero basis. If records are truly unrecoverable and there's no reasonable basis for an estimate, the default position is that distributions are fully taxable. This may be the conservative choice in some cases.

An advisor who specializes in inherited IRAs can help you determine whether the reconstruction effort is worth it — a $30,000 recovered basis across a 10-year window can save $9,000–$12,000 in federal taxes at common bracket rates.

Inherited IRA Basis and the SECURE Act 10-Year Rule

The SECURE Act's 10-year depletion requirement changes the math slightly versus the old stretch IRA. Under the stretch IRA, basis was recovered slowly over a lifetime — small amounts each year. Under the 10-year rule, distributions are concentrated into a decade, so the nontaxable fraction of each annual distribution recovers basis faster.

Two planning observations:

• Front-loading vs. back-loading distributions affects how quickly basis is recovered. Front-loading pulls basis recovery earlier (reducing taxable income in high-income years), while back-loading defers it. Modeling this is part of the withdrawal optimization work an advisor does.
• At year-10 full depletion, any remaining basis is recovered in full. If you've been computing the nontaxable fraction correctly all along, by the time the account hits zero, so does your remaining basis — everything worked out. If you haven't been tracking, year 10 may leave unrecoverable basis on the table.

For more on withdrawal pacing, see the Inherited IRA 10-Year Withdrawal Optimizer and the six inherited IRA tax strategies guide.

Common Mistakes That Cost Beneficiaries Thousands

Aggregating inherited and own IRA for the pro-rata calculation. This is the most frequent error. If you have $200,000 in your own traditional IRA (no basis) and you inherit a $200,000 IRA with $50,000 of basis, the wrong calculation would dilute the nontaxable percentage across $400,000 — cutting it in half. The correct calculation uses only the inherited $200,000 in the denominator. The difference across the 10-year window is material.

Never filing Form 8606 as a beneficiary. If you don't file, you leave no record of the inherited basis. When the account is depleted in year 10, there's no paper trail to support a nontaxable recovery.

Assuming the custodian will handle it. The custodian reports gross distributions on Form 1099-R. They don't know the basis — that's your responsibility to track and report. The IRS will tax you on the gross unless you file Form 8606 to claim the nontaxable portion.

Missing the decedent's year-of-death Form 8606. In the year of death, someone needs to file a final return for the decedent. If the decedent made non-deductible contributions that year, the year-of-death Form 8606 should be filed (by the estate or executor) to document that final contribution in the basis total that transfers to the beneficiary.

Get matched with a specialist

A fee-only advisor specializing in inherited IRAs can ensure the basis in your inherited account is documented, tracked, and recovered on Form 8606 — and integrate that into a bracket-optimized 10-year withdrawal plan.

Fee-only · No commissions · Free match · No obligation

Sources

1. IRS Publication 590-B (2025), "Distributions from Individual Retirement Arrangements," section on Inherited IRAs with basis: irs.gov/publications/p590b. Basis rules for beneficiaries governed by IRC § 408(d)(2).
2. IRS Instructions for Form 8606 (2025): "If you are required to file 2025 Form 8606 for IRAs inherited from more than one decedent, file a separate 2025 Form 8606 for the IRA from each decedent. If you take distributions from both an inherited IRA and your IRA, and each has basis, you must complete separate Forms 8606." irs.gov/instructions/i8606.
3. IRS Form 8606 (2025 version): irs.gov/pub/irs-pdf/f8606.pdf. Part I used by beneficiaries to calculate the nontaxable portion of inherited IRA distributions.
4. Kitces, M. "Reconstructing Lost IRA Basis to Avoid Double Taxation." Nerd's Eye View: kitces.com. Covers basis reconstruction methodology and late Form 8606 filing options.

Rules verified against IRS Publication 590-B and Form 8606 instructions current as of May 2026. The basis tracking rules themselves have not changed under recent legislation (SECURE Act, SECURE 2.0, OBBBA). No factual claims in this page are affected by the OBBBA (2025) or the Social Security Fairness Act (2025).