The IRS pulled an all-nighter.
The IRS, which was unable to process returns for several hours as a result of the outage, extended the filing deadline by one day to April 18 at midnight. (Don't worry, you don't need to do anything to get the additional time.)
"It's kind of a windfall to the procrastinators," said Mark Steber, chief tax officer at Jackson Hewitt.
The IRS blamed the system outage on a hardware issue.
"IRS teams worked hard throughout the night," Acting Commissioner David Kautter said Wednesday in a statement. "We are back up and running. The overnight performance means that the IRS is current with all of the tax submissions, and no backlog remains."
Millions of Americans wait until the last day to submit their returns, and it's the busiest tax day of the year for the agency.
The issue became apparent early Tuesday morning, according to tax professionals. Systems were working again by late afternoon.
The IRS said taxpayers were still able to prepare their tax returns electronically Tuesday if they were using software providers like TuboTax, H&R Block, or Free File. The issue was filing the returns to the IRS.
The agency said Wednesday it has accepted more than 14 million tax submissions since its processing systems reopened.
Kautter told members of Congress on Tuesday the problems appeared to be related to the "transmission" of tax returns from software providers.
H&R Block, Jackson Hewitt and TurboTax told CNNMoney they held the returns and submitted them once the IRS was able to accept e-filed returns again.
"We are always busy on the last day of tax season. This didn't really change how we operate," said Andy Phillips from The Tax Institute at H&R Block.
The IRS also had some issues accepting some forms of payment Tuesday. The system that allows filers to pay directly through their bank accounts wasn't functioning properly.
"For people who are getting a refund, there was no real impact at all," said Steber.
--CNN's Julia Horowitz contributed to this report
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