2023 TurboTax based the 2024 estimated tax calculation on your 2023 tax liability, AGI and the assumption that your tax withholding in 2024 will be the same as in 2023. If your tax withholding in 2024 ended up being lower, the 2024 estimated tax payments determined by 2023 TurboTax will have been too low unless you indicated to 2023 TurboTax that your 2024 tax withholding would be the lower amount.
When calculating the quarterly estimated tax payments, 2023 TurboTax took, depending on AGI, 100% or 110% of your 2023 tax lability, subtracted the assumed or indicated withholding amount, then divided by 4.
