The tax system, including filing procedures and reporting rules for many deductions and credits, is based on an annual system. A three-month or six-month extension would require lawmakers to decide how to handle those procedural issues.

“It’s not as easy as going in and changing the dates,” Barthold said in response to a question at the BloombergBNA Tax Policy & Practice Summit Tuesday in Washington.

Barthold’s office is the nonpartisan official scorekeeper for tax legislation in Congress.

Tax rates on income, capital gains, dividends and estates are scheduled to increase in January as part of the $607 billion fiscal cliff that Congress is trying to avert.

There has been some discussion in Congress of a short-term extension of tax cuts first enacted during President George W. Bush’s administration. On Sept. 6, Senator Richard Durbin, an Illinois Democrat, said lawmakers should consider a six-month delay in the cliff paired with deficit reduction. He made those comments in Charlotte, North Carolina, at the Democratic National Convention.