So I pay between April and October a few times to pay off the balance? You can do that.
Do I mark that anywhere on the 1040 I file by October 15th ? There is no place on the 1040 to do that ... the IRS knows what you paid ... just send in any balance due you did not already pay.
Or how to calculate the late payment penalty? The IRS will bill you for any underpayment or late payment penalties or interest after you file. This is nothing you can do yourself.
