It tells you on the irs website when to expect it.
http://www.irs.gov/Refunds
Get up-to-date refund information using Where's My Refund? or the IRS2GO mobile app. Where's My Refund? is updated once every 24 hours, usually overnight.
Refunds are generally issued within 21 days after we receive your tax return. You should only call if it has been longer.