About 90 percent of IRS operations were closed during the shutdown, putting the agency about three weeks behind what it says was already a tight schedule.
"Readying our systems to handle the tax season is an intricate, detailed process, and we must take the time to get it right," Werfel said. "The adjustment to the start of the filing season provides us the necessary time to program, test and validate our systems so that we can provide a smooth filing and refund process for the nation's taxpayers. We want the public and tax professionals to know about the delay well in advance so they can prepare for a later start of the filing season."
The heads-up is small solace for people banking on early returns in 2014.
"Those who file early because they get a return and have bills to pay are not going to be pleased," said certified public accountant Morgan Andersen of M. Andersen & Associates.
He acknowledged that, for the general populace, most of whom owe taxes and file at the April 15 deadline, the change won't affect them.
"But for the accountants," he said, "it gives us a shorter time to get things done."
Andersen, though, has learned how to "roll with the flow" after last year's budget squabbles forced tax-preparation software companies to release their products late to consumers. "It goes back to Congress not being able to get its act together."
According to a Wednesday release from the IRS, the shutdown came just as workers were programming, testing and deploying more than 50 IRS systems used to handle processing of nearly 150 million tax returns.
Some of those returns are processed at a large IRS facility in Ogden which, at peak season, can employ close to 7,000 workers.
The agency says that updating these core systems is a complex, year-round process with the majority of the work starting at the fall of each year.
Due to the shutdown, the agency said it will not process paper tax returns before the start date. Taxpayers will receive their refunds faster by using e-file with direct deposit.
The April 15 filing deadline is set by law, but the IRS reminds taxpayers that they can request an automatic six-month extension to file their tax return.
Since the end of the shutdown, the IRS has seen heavy demand on its toll-free telephone lines, walk-in sites and other services. During the closure, the agency received 400,000 pieces of correspondence.
"In the days ahead, we will continue assessing the impact of the shutdown on IRS operations, and we will do everything we can to work through the backlog and pent-up demand," Werfel said. "We greatly appreciate the patience of taxpayers and the tax professional community during this period."