The IRS is sitting on $1.4 billion in unclaimed tax refunds, and taxpayers are running out of time to grab their cash.

These tax refunds are from 2015, and they belong to about 1.2 million taxpayers who didn't file a return that year, according to the IRS.

In order to claim the money, taxpayers must submit their 2015 tax returns by April 15. If these people fail to turn in their Form 1040, the cash goes to the U.S. Treasury.

Generally, you have three years from the due date of your tax return to claim your refund.

The IRS may continue to hold your 2015 refund if you haven't submitted returns for 2016 and 2017.

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"Most likely if you have an unclaimed refund, you just never filed your return," said Susan Allen, CPA and senior manager of tax practice and ethics for the American Institute of CPAs.

"The common thing is that maybe you thought you didn't have a filing requirement or your income is too low, but you could still be entitled to a refund," she said.

There is no penalty for submitting a late return if you're due a refund.

The IRS isn't as kind to late filers with balances due; those taxpayers are on the hook for penalties.