Date ES penalty stops

Taxpayer just figured out that she will be underpaid for 2021 because she did not have withholding on her unemployment compensation. She wants to avoid the ES penalty. She's a waitress and higher withholding for the rest of this year is not in the cards. So she will make an ES payment soon to be safe from the ES penalty for the rest of the year. If she makes the payment on, say, July 22, will that be the date used to calculate the penalty regardless of whether she uses the 2nd quarter or the 3rd quarter ES voucher? Or would using the 3rd quarter voucher cause the payment to be treated as though she paid it on Sept. 15?

I guess I could look it up but I'm sure one of you out there knows the answer cold. Thank you.

July 22

OK, that's good. And that answer is regardless of which voucher she uses?

I would instruct her to use the Q2 voucher.

No need to take on unnecessary risk.

Or she could easily make a payment using the IRS2Go app on her phone. So sign up required and payments are credited quickly. She can even schedule the date for payment in advance.

I would also instruct to use the 2nd qtr voucher.