April 15 is the filing deadline for the U.S. income tax. The Internal Revenue Service (IRS), the federal agency responsible for collecting income tax revenues, depends on U.S. citizens to voluntarily follow the law and calculate and pay their income tax. Most people calculate and send in their taxes themselves, using forms provided by the government. People with complex finances use professional tax preparers to calculate and file their tax returns. In the 1990s, the IRS began accepting tax returns online, making it possible for people to calculate their tax payments with computer software and submit their payments via the Internet.