@MaxRLC as long as the envelope for a paper file is posted marked by 10.16 or efiled by 10.16, the IRS will give your payment credit as of the 16th, even if they process it later.
Yes, because of the speed of efiling, there is less "bank float" and the payment is more likely to be debited quicker than if you mail.
However, don't be fooled by mailing,,,,,, that tax return goes to a bank lockbox and the bank is going to rip open the envelope the same day it is received and deposit the check - and then the paper goes to the IRS for processing. So if you think you have weeks for the check to clear, that is not how it works. the Banks have 24 hours from receipt of the envelope to deposit the check (I used to work for a large bank that processed these envelopes).
I do not beleive the software will let you choose a debit date past the 16th. if it does and you do choose a date past the 16th, then it will be late and there are late charges and interest that the IRS will bill you for.
