Does the payment sent with the extension also count as an estimated tax payment?

[xmasbaby0]

Your extension gave you extra time to prepare your 2018 tax return documents.  It did not give you extra time to pay.  If you did not pay your estimated 2018 tax due by April 15, 2019 then when the IRS receives your 2018 return and your payment, they will calculate your penalty/interest and bill you later.  TurboTax will not calculate the penalty or interest.

You have until October 15, 2019 to e-file your 2018 tax return.  After that, e-filing for 2018 will be shutting down, and a 2018 return will have to be printed, signed and mailed instead.  The online software will also be shutting down, so if you are not finished preparing your 2018 return by then, you will have to download desktop software to a full PC or Mac to finish the return.

When you requested your extension you were supposed to pay your estimated tax due.  Did you enter the payment you made into your tax return?  Go to Federal>Deductions and Credits>Estimates and Other Taxes Paid>Other Income Taxes  This will show up on line 17 of your Form 1040

[VolvoGirl]

If your extension payment did not automatically show up on 1040 Schedule 5 line 71 which goes to 1040 line 17 you need to enter it. So make sure it's not already there before you enter it!

You can type estimates paid in the search box at the top of your return and click Find and it will give you a link to Jump To the screen where you enter Extension Payments.

To enter the amount you paid with an extension (including state extension)  go to
Federal Taxes (or Personal for desktop H&B version)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Update button

Next page second section Payments with Extension
Either Visit All or Click Start or Update by the extension you paid