The Internal Revenue Service said Tuesday it will begin accepting 2012 tax filings on Jan. 30, eight days later than originally planned.
The delay means millions of early-filing taxpayers will have to wait until February at the earliest for a refund.
More than 120 million households should be able to start filing tax returns on Jan. 30, the agency said.
"This date ensures we have the time we need to update and test our processing systems," IRS acting Commissioner Steven Miller said in a statement.
The delay stems from the Jan. 2 enactment of tax law changes made to resolve the "fiscal cliff."
The IRS could not write certain tax forms and tables without knowing how the law might reshape the U.S. tax code.
About 18 million taxpayers usually file tax returns in January, and 98 percent of them receive a refund, said tax preparation company H&R Block Inc., citing IRS data. These taxpayers often include low-income individuals who file returns early to get refundable tax credits.
The 11th-hour fiscal cliff bill set up another potentially even more troublesome convergence of events in late February and early March. That is when the bill's two-month delay in spending cuts will end. It is also when the federal government again will hit its borrowing limit and when authorization for the federal budget runs out.
It was unclear what impact these events might have on tax refunds.