The IRS states that 9 of 10 refunds are issued within 21 days of processing (https://www.irs.gov/taxtopics/tc152.html). What that normally means is -- if you requested a paper check -- it may take a month or more to receive it, since the mail process will add additional time.
If you e-filed more than 21 days ago, then IRS will research the status of your return (IRS Refund Hotline 1-800-829-1954). If you filed a paper return, then they will not research your return prior to 6 weeks from your date of mailing.
If your return was delayed due to claiming the Earned Income Credit or Additional Child Tax Credit, then it could take longer, as IRS will not release refunds pertaining to those returns until February 15.
