abctax55 - Word of advice, I usually include the first estimate amount with the extension payment with the anticipation of the overpayment being applied.  That way, if the guestimate is wrong, 2024 is covered and only the 1st qtr 2025 estimate is (possibly) low. 

Yup, been doing that for years. Client's still don't understand it but it has sure saved them penalties when the projection is too low.