• May 17 is your last chance to claim your 2020 tax refund by filing your federal return.
• As of May 6, there was still an estimated $1 billion in unclaimed refunds from tax year 2020, and the median payment was $932, according to IRS data.
• Your pending refund could include 2020 pandemic relief, such as the recovery rebate credit if you didn't receive a stimulus check.

May 17 is your last chance to file 2020 returns and claim your refund, which could include missed pandemic relief, experts say.

As of May 6, there was still an estimated $1 billion in unclaimed refunds from tax year 2020, and the median payment was $932, according to the IRS.

There is no late filing penalty if you're owed a refund. But roughly 940,000 taxpayers could surrender their 2020 refund payment if they don't file by May 17, the agency said in May.

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The deadline is "terribly important" because there's a three-year refund expiration after each tax deadline, said certified public accountant John Karls, partner at accounting firm Armanino.

The 2020 tax deadline was postponed to May 17, 2021, amid the pandemic — and the three-year deadline to file 2020 returns and collect refunds is now upon us.

"If you let if you let it slip, there's nothing anybody can do," said Bill Smith, national director of tax technical services at financial services firm CBIZ MHM. "You won't get your refund when the statute of limitations has run out."

Plus, "2020 was the year of with additional tax breaks or credits" for certain filers, Karls noted.  

That could include the recovery rebate credit, a nonrefundable tax break for eligible filers who didn't receive economic impact payments. These payments, also known as "stimulus checks," are linked to coronavirus relief. 

If you're eligible for relief and don't file your return by May 17, you're "truly leaving dollars on the table," Karls added.

Create a 'roadmap' for past filings

If you still haven't filed 2020 returns and are feeling overwhelmed by where to begin, the IRS has tools to make the process easier, according to Karls.

You can log into your free IRS online account to access your wage and income transcripts, which include certain tax forms, such as Forms W-2, 1098, 1099 and 5498.

"For many taxpayers, this is by far the quickest and easiest option" for collecting missing information, according to the IRS.

"That's going to give a roadmap" and let you know if you need to contact a past employer, Karls said.

But it may take time to collect the missing forms, so you should start the process as soon as possible, he said.

You can also collect missing tax forms online via your bank or other financial institutions.