There is free money to be had, but you don’t have much time: Just like last year, the Internal Revenue Service says about one million taxpayers have yet to collect nearly a billion dollars in federal refunds from the 2013 tax year.

The IRS announced on Wednesday that taxpayers have until April 18 to file a 2013 tax return, if they haven’t yet.

Under federal law, most taxpayers have a three-year window to claim an IRS refund. That means once the April 18 deadline passes, taxpayers will no longer have the opportunity to recoup their 2013 refunds. Any money that isn’t claimed in time will go into the U.S. Treasury, never to be seen again.

The IRS estimates that the midpoint for potential refunds for 2013 to be $763, with half being worth more than $763 and half are less.

“Students and many others may not realize they’re due a tax refund. Remember, there’s no penalty for filing a late return if you’re due a refund,” IRS Commissioner John Koskinen said in a statement.

However, the IRS does note that refund checks will be held if the taxpayers haven’t filed returns for 2014 and 2015. The funds will also be applied to any amounts you owe to the IRS or state tax agencies, as well, and could be used to offset unpaid child support or overdue federal debts, including student loans.

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