More than $1 billion has yet to be claimed in tax returns, and the clock is ticking on Americans.

The Internal Revenue Service said Monday that around 940,000 people in the U.S. need to submit tax returns for the 2020 tax year by May 17.

"There’s money remaining on the table for hundreds of thousands of people who haven’t filed 2020 tax returns," IRS Commissioner Danny Werfel said in a news release. "We want taxpayers to claim these refunds, but time is running out for people who may have overlooked or forgotten about these refunds."

The federal tax collector urges taxpayers to gather their W-2, 1098, 1099 or 5498 from their employer or bank ahead of the deadline. Alternatively, the service recommends ordering a free wage and income transcript using its "Get Transcript Online" tool.

The IRS said taxpayers won't be able to receive any 2020 refunds if they haven't filed a return for 2021 and 2022. The agency said this is to make sure they don't owe money.

What is the average 2020 median refund?

The average median refund for the 2020 tax year is $932, the IRS said.

In Texas, where a potential an estimated 93,400 people have yet to claim their refunds, the average median refund is $960. The highest average median refund is in Pennsylvania at $1,031 followed by New York at $1,029.

The agency listed median potential refunds for each state and how many individuals have not filed in the official release.

2020 tax return deadline pushed due to COVID

The deadline to claim old tax refunds is typically on April 15 but the three-year window for 2020 was pushed to May 17 because of the COVID-19 pandemic.

"People faced extremely unusual situations during the pandemic, which may have led some people to forget about a potential refund on their 2020 tax returns," Werfel said. "People may have just overlooked these, including students, part-time workers and others. Some people may not realize they may be owed a refund. We encourage people to review their files and start gathering records now, so they don’t run the risk of missing the May deadline."

When is the 2024 tax return deadline?

The nation's 2024 tax season deadline is April 15, 2024. The IRS said it expects over 128.7 million individual tax returns to be filed by then.

The tax season officially started on Jan. 29. More than 71.5 million individual tax filings have been sent this season, according the IRS's latest update on March 15.