Some tax refunds may be delayed this year. Here's why.

Three weeks before the official end of tax season, the IRS has issued nearly 50 million tax refunds. But many others are still waiting for a refund. In addition, the agency has a backlog of nearly 7.5 individual tax returns it's processing from prior years — far more than the 1 million it usually has going into a tax season. When it has been longer than 21 days since the return was electronically filed. When it has been six weeks or more since the return was mailed. If the "Where's My Refund?" tool instructs someone to contact the IRS.

Here's why some refunds might be taking longer this year — and what taxpayers might do about it.