First of all, let me make clear that I am not a tax professional...
For the sake of argument, let's assume that I mail my individual income tax return, form 2210, the additional tax owed etc. etc. on 04/01/16 (payment by personal chek). Line 16 of form 2210 wants to know how many days was the payment made before 04/15/16.
Does the IRS consider 04/01/16 as the day the payment was made, or do I have to estimate when the IRS will cash the check as the date when payment was made?