How can I revise a federal extension and payment amount after it has been filed?

You do not need to change the amount on your extension filing.  It is an estimate and a placeholder for the IRS.  If you are calculating your tax liability, or re-estimating it and wish to pay an additional amount to avoid any underpayment penalties assessed when you file your return, you can print a voucher and mail it and a check for payment or you can pay online through the IRS website.  The voucher has the mailing instructions and information you need to include on your check to be sure it is applied correctly.

you have two choices.

go to IRS website make a payment page and select

• EXTENSION for an additional payment
• BALANCE DUE for a final  payment.

if you used balance due before filing enter the payment(s) on Schedule 3 Line 13z.

For type, use "Bal Due <date>"

It seems TurboTax makes that line hard to find, so you may want to go with EXTENSION.

@jak927 

Either way, pay everything you owe by April 18th.