The IRS is warning taxpayers that they may be leaving more than $1 billion on the table.

The federal tax collector said Monday that roughly 940,000 people in the U.S. have until May 17 to submit tax returns for unclaimed refunds for tax year 2020, which total more than $1 billion nationwide.

The average median refund is $932 for 2020. Texas (93,400), California (88,200), Florida (53,200) and New York (51,400) have the largest number of people potentially eligible for these refunds.

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IRS Commissioner Danny Werfel said in a statement: "We want taxpayers to claim these refunds, but time is running out for people who may have overlooked or forgotten about these refunds. There’s a May 17 deadline to file these returns so taxpayers should start soon to make sure they don’t miss out."

For people who need to file a return, the IRS advises taxpayers to request their W-2, 1098, 1099 or 5498 from their employer or bank — or order a free wage and income transcript using the "Get Transcript Online" tool at IRS.gov.

Taxpayers typically have three years to file and claim tax refunds, otherwise the money becomes the property of the U.S. Treasury.

Generally the deadline to claim old refunds falls around the April 15 tax deadline, but this year the three-year window for 2020 unfiled returns was postponed to May 17, because of the COVID-19 pandemic. But if taxpayers haven't filed a return for tax year 2021 and 2022, any 2020 refunds would be withheld until they file for those years as well to make sure they don't owe.

Werfel said "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."

Tax season officially began on January 29.

According to the latest tax season statistics, more than 71.5 million individual tax filings have been submitted to the IRS this season.