Please note that the IRS extended their tax deadline to May 17, 2021. HOWEVER, the states have NOT extended their deadline (at this time) and returns for them are due on April 15, 2021. In addition, if you send in estimated tax payments, the first payment date for these are still April 15, 2021.
FYI - if you plan on filing an extension on your returns, it only gives relief to the late filing penalty. If you owe money to the IRS or state, you need to pay it by the April 15 (state)/ May 17 (IRS) deadline in order to avoid owing penalties and interest.