The IRS began processing tax returns Monday. For filers who submit their returns electronically using direct deposit, refunds are generally issued in less than 21 days. There is a caution from the tax agency, however, that urges “taxpayers not to rely on receiving refund by a certain date, especially when making major purchases or paying bills.

You may have filed early but your refund could still be delayed for a number of reasons. Here's what to know, and how to check on yours.