TurboTax sells both online and download tax programs. The online programs only allow you to do one tax return. The download program allows you do do an unlimited number of returns*, including preliminary/projected returns. They will not be totally accurate, for 2024, because they are based on 2023 rules and tax tables. But, for most people, it will be "close enough".
I make a copy of my 2023 return, name it 2024 preliminary and then adjust the numbers for 2024. It can be modified numerous times. Or you can just start a preliminary from scratch.
*You can only e-file 5 returns. Any additional returns would have to be paper filed.
