- February 29 – Payers must file information returns, such as Forms 1099, with the IRS. This deadline is extended to March 31 when the forms are filed electronically.
- February 29 – Employers must send W-2 copies to the Social Security Administration. This deadline is extended to March 31 for electronic filing.
- March 1 – Farmers and fishermen who did not make 2015 estimated tax payments must file 2015 tax returns and pay taxes in full to avoid a penalty.
- March 15 – 2015 calendar-year corporation income tax returns are due.
- March 15 – Deadline for calendar-year corporations to elect S corporation status for 2016.
- March 31 – Large employers must furnish Forms 1095-C to employees.