If you meet certain requirements, you may be able to deduct your contributions to a traditional IRA, although deductions are phased out at relatively low income levels. Yet even if you don’t qualify for a tax deduction, you still can contribute to an IRA, especially if you aren’t eligible to make Roth IRA contributions. You also might have “after-tax” assets in a 401(k) or other retirement plan that you want to roll over into an IRA. But having both deductible and nondeductible assets in the same account can complicate matters when it’s time to withdraw money.

Deductions for contributions to an IRA are phased out if you (or your spouse) participate in an employer-sponsored retirement plan and your adjusted gross income (AGI) exceeds an annual limit. For example, the phaseout for 2017 occurs between $62,000 and $72,000 of AGI for a single filer who is an active plan participant and between $99,000 and $119,000 for a joint filer. The range is from $186,000 to $196,000 if your spouse is the participant and you file jointly.

Meanwhile, your ability to contribute to a Roth IRA, which offers the promise of future tax-free payouts, is phased out in 2017 between $118,000 and $133,000 of AGI for a single filer and between $186,000 and $196,000 for a joint filer.

Even if you don’t qualify to make tax-deductible contributions to a traditional IRA or after-tax contributions to a Roth, you still can put money into a traditional IRA on a nondeductible basis. You also can choose to forego deductions for contributions if that suits your purpose, but you’ll have to file Form 8606 for nondeductible contributions with your tax return to notify the IRS. The deadline for making IRA contributions is the tax return due date for the year of the contribution, so you have until April 17, 2018, to complete the forms for 2017.

Besides making nondeductible contributions to a traditional IRA, you might

roll over after-tax assets from a 401(k), or other employer plan, to a traditional IRA. While you aren’t technically required to file a Form 8606 in the year of the rollover, when you take distributions from the IRA you must use the form to report any portion representing after-tax assets. That portion won’t be subject to income tax.

If your IRA has nondeductible assets, the tax-exempt portion of any withdrawal will be figured on a pro rata basis, taking into account all of your IRAs. Suppose you’ve deposited $20,000 in nondeductible contributions to an IRA and the total value of all of your IRA assets is $100,000. Based on the 20% allocation, if you take a distribution of $10,000, $2,000 would be tax-free and the other $8,000 would be subject to tax.

If all of that seems unnecessarily complex, keep in mind that mistakes could result in unnecessary tax and an early withdrawal penalty if you’re under age 59½.