Retirement savers need to pay close attention to their income tax filings this year because of pandemic-related changes to rules for required withdrawals.

Even in normal times, the rules for mandatory minimum withdrawals can be confusing, and are even more so this year because of a mash-up of tax changes and virus relief programs. If you get things right, you can avoid paying unnecessary taxes, financial advisers say.

“The stakes are high,” said Cheryl Costa, a certified financial planner near Boston.

Generally, savers must start taking money out of tax-advantaged retirement accounts, like 401(k)s and traditional individual retirement accounts, annually after they reach a certain age. (More about this below.) The tax penalty for missing a withdrawal is steep: It is half of the amount that should have been withdrawn, although the Internal Revenue Service will drop the penalty if you have a reasonable explanation.

But last March, as part of its pandemic relief program, the federal government waived the annual “required minimum distributions,” or R.M.D.s in tax lingo, from most retirement accounts. The suspension was aimed at helping older Americans avoid withdrawing money during what was, at the time, a virus-induced stock market tumble.

That was good news for people who didn’t immediately need the cash to live on. They could keep the money invested in hopes of a market recovery and avoid paying taxes on withdrawals.

The catch was that some people had already taken their minimum distributions in the early months of 2020, before the virus hit. So the I.R.S. announced a fix last summer: If people had withdrawn funds they didn’t need, they could redeposit all or part of the money by Aug. 31. (Normally, savers have just 60 days to change their minds.)

Now, to this year’s tax season, and people who redeposited their funds are receiving 1099-R forms showing the full amount of the withdrawal, even though the money was returned. “Many think the form was sent to them in error,” Ms. Costa said.

The forms are correct — but they only report distributions, so it may appear as though the amount is taxable. Taxpayers must report the withdrawal as a tax-free rollover on their tax returns, said Ed Slott, a certified public accountant in New York and an authority on I.R.A.s.

“You can’t ignore it,” Mr. Slott said. “You have to tell the I.R.S. the story about what happened.”

Here’s how to do that: The amount in Box 1 of the 1099-R form is entered on Line 4a of Form 1040, “I.R.A. distributions.” Then, on Line 4b, “taxable amount,” you should enter zero — assuming you returned the full distribution. If you kept part of the withdrawal, that amount is taxable and you should enter it on Line 4b. For a 401(k) withdrawal, you would use Lines 5a and 5b, Mr. Slott said.

If you’re using tax preparation software, the document should print out with the word “rollover” entered next to the zero, Mr. Slott said. Someone completing a paper form would need to write in the word “rollover.” That will treat the withdrawal as a nontaxable event. (Usually, R.M.D.s aren’t eligible for rollovers, but the I.R.S. made an exception for 2020.)

Some clients who returned their R.M.D.s have had pleasant surprises on their tax returns, Ms. Costa said. Because their taxable income is lower than it would have been, some were able to deduct medical expenses or even qualify for the federal stimulus payments.

But if the minimum distribution isn’t properly reported as returned, those benefits could evaporate, Ms. Costa said.

“You don’t want to add insult to injury by paying taxes on a distribution that you returned,” she said.

Here are some questions and answers about R.M.D.s:

Is it OK if I kept the retirement withdrawals I made in 2020?

Yes. Returning the money was optional.

Are R.M.D.s waived for 2021?

No. The waiver applied only to withdrawals in 2020.

When do I have to start taking R.M.D.s?

It depends. A federal law passed in 2019 called the SECURE Act, for Setting Every Community Up for Retirement Enhancement, raised the starting age for taking R.M.D.s to 72, from 70½.

The new age 72 threshold applies to those who turned 70½ after 2019 — or, put another way, those whose 70th birthday was July 1, 2019, or later. For everyone who turned 70 before that date, the starting age is 70½.

What about Roth I.R.A.s?

There are no required withdrawals for Roth I.R.A.s during the account owner’s lifetime.

Someone other than a spouse who inherits a Roth generally must take minimum withdrawals within a certain period — but that requirement was also waived for 2020, Mr. Slott said.