The IRS says there's still time for Americans to claim the nearly $1 billion they left on the table in 2013

When an estimated 1 million of the US' 300-plus million population didn't file their federal income tax returns for 2012, they lost out on $950 million in unclaimed refunds, the IRS said on Thursday.

Since the returns were for the year 2012, tax payers would have gotten that money in 2013.

"We especially encourage students and others who didn't earn much money to look into this situation because they may still be entitled to a refund," the IRS' commissioner, John Koskinen, said in a statement. "Don't forget, there's no penalty for filing a late return if you're due a refund."

The IRS estimated a median potential refund of $718. Those refunds belong to the US Treasury if they aren't claimed within three years. That means taxpayers have until this year's April 18 deadline (April 19 in Maine and Massachusetts) to file a return for 2012 to claim their refund if they have not already.

Idahoans with outstanding returns were owed a median potential refund of $607, the smallest of any state, while Wyoming taxpayers owed refunds came out on top with a median potential refund of $851.

The refunds can't be claimed if the taxpayer still hasn't filed returns for the 2013 or 2014 tax seasons.