WASHINGTON (AP) — The Internal Revenue Service has a message for taxpayers eager to learn the status of their tax refund: Please don't check the IRS website every five minutes — once a day is enough.

The IRS says its "Where's my refund?" website and smartphone app are being overwhelmed by eager taxpayers. The agency says its systems are only updated once a day, usually overnight, and the same information is available on the website, the IRS2go smartphone app and IRS toll-free phone lines.

The IRS provides three updates: when the tax return is received, when the refund is approved and when the refund is sent. To avoid delays, the agency says the best time to check on refunds is evenings and weekends.

"I think what we're seeing is just part of the natural evolution in the refund process," said IRS spokesman Terry Lemons. "Twenty-five years ago, you desperately checked the mailbox every day."

Lemons said the number of inquiries is up over last year, probably because it is easier to check on smartphones and computer tablets.

Nine out of 10 taxpayers typically receive refunds in less than 21 days when they file returns online and get refunds deposited directly into bank accounts, the agency said.

The IRS is receiving more than 1 million returns a day and volume is expected to increase in the coming days, Lemons said. About 75 percent of individual filers get refunds. Last year they averaged $2,803.

"Every year our most common question is about people's refunds," Lemons said. "For a lot of folks this is the biggest check they will see all year."