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The Internal Revenue Service said that following Congress' tax law changes last week it won't begin processing individual income tax returns until Jan. 30, eight days later than usual.

The American Taxpayer Relief Act, which was enacted on Jan. 2, included retroactive changes to the 2011 tax year as part of the fiscal cliff deal.

The IRS said it will begin accepting tax returns on Jan. 30 after updating forms and completing programming and testing of its processing systems, reflecting "the bulk of the late tax law changes enacted Jan. 2."

Read more: Results of the 9 Most Contentious Fiscal Cliff Tax Issues

"We have worked hard to open tax season as soon as possible," IRS Acting Commissioner Steven T. Miller said in a statement. "This date ensures we have the time we need to update and test our processing systems."

The IRS points out there is no advantage to filing on paper before the opening date, and taxpayers will receive their tax refunds much faster by using e-file with direct deposit.

The agency said the "vast majority of tax filers - more than 120 million households - should be able to start filing tax returns starting Jan 30."

The remaining households can start filing in late February or into March because of the need for "more extensive form and processing systems changes," including people claiming residential energy credits, depreciation of property or general business credits.

Most of those in that group file more complex tax returns and typically file closer to the April 15 deadline or obtain an extension, the IRS said.