While the primary form used to file income taxes, Form 1040, is due on April 15 every year, other due dates apply to other forms of taxes, according to the IRS. Those who must pay estimated taxes typically pay them by the 15th of January, April, June and September.
Employers must file Form 940, the Federal Unemployment Tax Return; Form 945, the Annual Return of Withheld Federal Income Tax; and their employees W-2 forms on January 31 each year. All Forms 1099 and reports of tip income must be filed by February 28. Employers must also file W-2s with the Social Security Administration by February 28, and 1099s with the SSA by March 31, explains the IRS.