If I use a state's website on 12-31-23 to schedule a tax pmt, but the earliest eff date available is 1-2-24, can I still use 2023 as the tax year for the transaction?

[DoninGA]

It depends on your state's tax code on whether the estimated payment on 01/02/2024 will be for tax year 2023.

However, most states follow the federal dates for making estimated tax payments.  For federal you can make an estimated tax payment for 4th quarter 2023 at any time on or before 01/16/2024.

[fanfare]

Just be careful to mark the payment for the correct tax year.

I made that mistake a couple of years ago.

@Killebrew3 

[rjs]

With regard to crediting the payment to your 2023 state tax, see the reply from DoninGA above.

However, if you are itemizing deductions on your federal tax return, you have to include the state tax payment in your itemized deduction for state and local taxes in the year that the payment was actually made. So you could end up with a payment of 2023 state tax that is deductible on your 2024 federal tax return, not on your 2023 federal tax return.