What Is Basis in an IRA? Roth vs. Traditional Basis Explained 2026

Basis in an IRA is the portion funded with after-tax dollars — money you've already paid income tax on. For a Roth IRA, all direct contributions are basis. For a traditional IRA, basis is only the nondeductible portion — contributions you couldn't deduct due to income limits or workplace plan coverage. Basis is tracked on Form 8606, filed for any year of nondeductible contribution, distribution, or Roth conversion.

quick_reference_all

Quick Facts

check_circleRoth IRA basis = total direct contributions ever made. Withdrawable anytime, tax-free, regardless of age or 5-year rule, per IRC §408A(d)(4).
infoTraditional IRA basis = nondeductible contributions only. Reported on Form 8606 for the year contributed.
infoConversion basis carries over. When you convert a traditional IRA to a Roth, your traditional IRA basis becomes Roth basis.
warningPro-rata rule applies to traditional/SEP/SIMPLE IRAs. Per IRC §408(d)(2), your basis is allocated proportionally across all your traditional IRAs combined when you take a distribution or convert.
check_circleForm 8606 is the IRS's basis-tracking form. File it for every year you make a nondeductible contribution, take a distribution from an IRA with basis, or do a Roth conversion. Keep copies indefinitely.

Roth IRA Basis: Simple

Roth IRA basis is conceptually clean. Every dollar you've contributed directly to a Roth IRA is basis (already taxed). Conversions you've completed add to your Roth basis (you paid tax at the conversion). Earnings on those contributions are not basis — they're tax-free if you meet the qualified-distribution test (5-year rule + age 59½ or other qualifying condition), but they aren't part of your basis pool.

The IRS ordering rules under IRC §408A(d)(4) treat your Roth IRA dollars in this order when you withdraw: contributions first (your basis), then conversions oldest-first, then earnings. As long as your withdrawal stays at or below your basis, it's tax-free and penalty-free regardless of age.

Traditional IRA Basis: More Complicated

Most traditional IRA contributions are deductible — they reduce your current-year taxable income, which means you haven't paid tax on them yet, which means they're NOT basis. They'll be taxed when you withdraw in retirement.

But under IRC §219(g), the deduction phases out at certain income levels if you (or your spouse) are covered by a workplace retirement plan. If your income is above the phase-out and you contribute anyway, those contributions are nondeductible — you've paid tax on them — they ARE basis.

The same is true if you ever made an after-tax contribution to a 401(k) that later got rolled into a traditional IRA, or if you previously converted nondeductible contributions back to traditional (rare, pre-2018).

To track this correctly, file Form 8606 for every year you make a nondeductible contribution. The form keeps a running tally of your basis. When you eventually take distributions or convert, the form calculates how much of each transaction is non-taxable basis vs. taxable pre-tax dollars.

The Pro-Rata Rule and Basis

This is where most readers get hurt. When you take a distribution from a traditional IRA OR convert traditional-IRA dollars to a Roth, the IRS does NOT let you cherry-pick basis dollars to come out tax-free. Under IRC §408(d)(2), basis is allocated proportionally across ALL your traditional, SEP, and SIMPLE IRAs combined — treated as one pool — for the calculation.

Worked example: you have $92,500 of pre-tax dollars in a rollover IRA from an old 401(k) and $7,500 of nondeductible basis in a separate traditional IRA. Total = $100,000, of which $7,500 (7.5%) is basis. If you convert $7,500 from the nondeductible-only IRA to a Roth IRA, the IRS treats only 7.5% of that conversion ($562.50) as tax-free basis recovery; the other 92.5% ($6,937.50) is taxable income.

This is why the Backdoor Roth strategy requires no pre-tax balances in any traditional/SEP/SIMPLE IRA — otherwise the pro-rata rule taxes most of the conversion. See the dedicated Pro-Rata Rule page for full mechanics.

Frequently Asked Questions

How do I know my IRA basis?

Look at Form 8606 — it's the IRS's running basis tracker. Line 14 carries forward your year-end traditional IRA basis. If you've never filed Form 8606, your basis is zero according to the IRS, even if you actually made nondeductible contributions. Reconstructing missed Form 8606 filings retroactively is possible (consult a CPA) but worth avoiding by filing each year.

Are all Roth IRA contributions basis?

Yes — direct Roth IRA contributions are basis by definition (you paid tax on the dollars before contributing). Roth conversions also add to basis (you paid tax at the time of conversion). Earnings inside a Roth IRA are NOT basis but become tax-free once the qualified-distribution test is met.

Do I need to file Form 8606 every year?

Only when one of these triggers fires: (1) you made a nondeductible traditional IRA contribution, (2) you took a distribution from a traditional IRA that has any basis, (3) you did a Roth conversion. If none of those happened in a given year, no Form 8606 is required. But you should keep the most recent Form 8606 with your tax records indefinitely — your basis carries forward decades.

Can I withdraw my IRA basis tax-free?

From a Roth IRA: yes — your direct contribution basis can be withdrawn at any age, anytime, tax-free and penalty-free. From a traditional IRA: not directly — the pro-rata rule under IRC §408(d)(2) forces a proportional allocation across pre-tax and basis dollars. You can't isolate basis-only withdrawals.