The original plan was for a Jan. 21, 2014 opening. However, about 90 percent of IRS operations were closed during the shutdown and some were shut down entirely, which set the agency back three weeks in its preparation for tax season.

"The late January opening gives us enough time to get things right with our programming, testing and systems validation," acting commissioner Danny Werfel said in a prepared statement.

The IRS encouraged taxpayers to use e-file or FreeFile as the fastest way to receive refunds. It notes new year-end tax planning information was added to IRS.gov this week. Many software companies are expected to accept returns before the opening and hold them until January 31. The IRS says there is no advantage to filing on paper before then because it will not process early returns.