I usually use the prior year TT to do some running estimate during the year until the next year's version is available. The only issue is any changes in deductions or tax brackets for 2025 etc will be slightly different so you have to compensate a little for those situations to make it work e.g. you can mock up a W2 from your YTD pay statement but maybe 401k contribution limits have changed, HSA deduction limits have changed etc, and maybe do the final tax table calculation by hand using 2025 tables. There may be other tax calculators which are up to date for 2025 more quickly than the TT release. Depends how complex your situation is - but remember to avoid underpayment penalty you need to hit 100% of 2024 tax (110% if AGI > 150k), or 90% of 2025 tax whichever is smaller, so your worst case you need to hit the "100/110% of 2024 tax" which is known but maybe more withholding than you need; did you work thru the interview under Other Tax Situations/Form W4 and Estimated Taxes to figure the amount you need.
