Nondeductible IRA

A nondeductible IRA is a contribution to a traditional IRA made with after-tax dollars because the taxpayer’s income exceeds the phase-out limit for IRA deductions. Though the contribution itself is not deductible, the account still grows tax-deferred, and the after-tax basis must be tracked to prevent double taxation on withdrawal.

How deduction phase-outs create nondeductible contributions

Tax law allows every working person to contribute up to an annual limit to a traditional IRA, but the contribution is only deductible if income falls below specified phase-out ranges. For 2024, a single filer with a 401(k) at work cannot deduct IRA contributions if their modified adjusted gross income (MAGI) exceeds roughly $77,000. The deduction phases out entirely by around $87,000. Married couples filing jointly with one spouse working have a much higher threshold, around $230,000, but even they face phase-outs.

When income exceeds the phase-out range, a taxpayer can still contribute to a traditional IRA—the law does not forbid it—but the contribution receives no tax deduction. That contribution is made with after-tax dollars, which is why it is called nondeductible. The account still grows tax-deferred, so the earnings on the contribution compound without annual tax, but the original dollars went into the account having already been taxed at ordinary income rates.

Why nondeductible IRAs exist in a high-income world

High-income earners quickly max out 401(k) plans (annual limit around $69,000 in 2024) and often cannot deduct IRA contributions due to income limits. A nondeductible IRA is a safety valve: rather than forgo an IRA contribution entirely, they contribute after-tax dollars. The contribution itself provides no tax break, but the tax-deferred growth is still valuable.

Many high earners view nondeductible IRAs as a stepping stone to more advanced strategies like the backdoor Roth. A backdoor Roth involves contributing to a nondeductible IRA, then immediately rolling it into a Roth IRA, converting the contribution to tax-free status. The nondeductible IRA itself is neutral; the value comes from the subsequent conversion.

The pro-rata trap: why other IRAs matter

The most dangerous feature of a nondeductible IRA is the pro-rata rule, which applies when someone has both nondeductible (after-tax) and deductible (pre-tax) IRA balances. When withdrawing from any IRA, the IRS treats all IRAs as a single pool and allocates withdrawals proportionally across the pre-tax and after-tax portions.

Suppose someone has $100,000 in a traditional IRA (all pre-tax contributions) and makes a $10,000 nondeductible contribution, creating $110,000 total. If they then convert the nondeductible IRA to a Roth, the IRS does not allow them to convert only the $10,000 nondeductible portion. Instead, the conversion is treated as 91% pre-tax ($100,000 / $110,000) and 9% after-tax ($10,000 / $110,000). The result: $9,091 of taxable income from the Roth conversion, even though the intended move was to convert only after-tax dollars.

This rule is why backdoor Roth strategies require eliminating all pre-tax IRA balances first, often through rollovers into a 401(k) (if one is available).

Tracking basis with Form 8606

The IRS requires anyone with nondeductible IRAs to file Form 8606 with their tax return, regardless of whether they withdrew money that year. The form tracks the running total of all nondeductible contributions ever made to any IRA, which becomes the taxpayer’s cost basis. At withdrawal, basis comes out tax-free; the remainder is taxed as ordinary income.

A taxpayer who contributes $10,000 nondeductible each year for five years and never withdraws will have $50,000 in basis. If they then withdraw $100,000, they owe tax on only $50,000 of the withdrawal. The other $50,000 is a tax-free recovery of their after-tax contributions.

Form 8606 must be filed every year the taxpayer owns a nondeductible IRA, even if no withdrawal occurs. Missing this filing can lead to double taxation (where the same dollar is taxed twice) and penalties. Divorce, death, or inheritance of an account with nondeductible basis also requires careful Form 8606 documentation to ensure the inherited IRA beneficiary calculates basis correctly.

The math of after-tax growth

Despite the tracking burden, nondeductible IRAs do offer tax-deferred growth. A $10,000 nondeductible contribution that grows to $15,000 over five years is taxed only on the $5,000 gain at withdrawal, not on the full amount. A comparable taxable brokerage account would have triggered tax on the gains annually, eroding the compounding.

The tax savings are modest compared to a fully deductible IRA, but they are genuine. For investors with a 30-year horizon and moderate returns, the tax deferral can still add up to meaningful wealth accumulation—especially when paired with other tax-advantaged strategies.

Who should consider nondeductible IRAs

Nondeductible IRAs make sense for high-income earners unable to contribute to Roth IRAs due to income limits and who have maxed out employer retirement plans. They are less attractive for people under the deduction phase-out limit, for whom a deductible traditional IRA is superior, or for those with no pre-tax IRAs who plan to convert the account to a Roth (in which case a backdoor Roth is the better route).

They are also useful for self-employed people who have maxed a SEP IRA or Solo 401(k) and want additional sheltered savings. A nondeductible IRA is separate from these plans and does not count against their contribution limits.

Common mistakes

The most frequent error is failing to file Form 8606, then withdrawing from a nondeductible IRA years later without proper documentation. The IRS will tax the entire withdrawal as if it were all pre-tax, creating a surprise bill. Another mistake is forgetting about the pro-rata rule and attempting a Roth conversion without realizing other pre-tax balances will drag most of the conversion into taxable income.

A third pitfall is commingling contributions across years without tracking which were deductible and which were not. Good recordkeeping—a spreadsheet noting the year, amount, and deductibility status of each contribution—prevents downstream confusion.

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