PORTLAND — The Internal Revenue Service says approximately 4,500 Maine taxpayers are owed about $3.7 million in unclaimed tax refunds.

WMTW-TV reports that Maine residents are among a million taxpayers around the country who haven’t claimed an estimated $1 billion in refunds for the 2011 tax year.

Taxpayers have until April 15 to file their tax returns. IRS Commissioner John Koskinen says taxpayers who did not file a 2011 federal income tax return are running out of time to claim the refund. He says refunds could be “substantial” for people such as students and part-time workers.

The IRS says the average unclaimed Maine refund is $645.