The income tax filing deadlines for individual filers and partnerships is on the 15th day of the fourth month after the end of the tax year, indicates the IRS. The tax filing deadline for corporations falls on the 15th day of the third month after the tax year's end.
Certain entities may be required to file other periodic disclosures. Employers are required to file quarterly social security and Medicare tax withholding returns on the last day of the first calendar month following the end of that quarter, explains the IRS. These employers are also required to file annual federal unemployment tax returns that are due on the last day of the first calendar month of the following year.