All tax returns must be filed, and payments made no later than the 20th day of the month after each filing period unless the 20th day falls on a Saturday, Sunday or City holiday. In those cases, the return and payment are due the following business day. Any tax return or payment submitted after the due date is considered late and is subject to penalty and interest.
Be advised: the cutoff time for timely filing a return and paying the tax through the MAT website is 4pm CST.