For 2022 1040 tax returns the due date this year was April 18, 2023. For late payment of tax, shouldn't interest charges begin on April 18th and not April 15th? Pro Series computes the interest from April 18th forward. However, a client of mine just got dinged by the IRS for the 3 extra days from April 15th. Is the IRS wrong or Pro Series? The regs I looked at refer to interest from the due date of the return.