to avoid an underpayment penalty you need to have paid (either thru withholding or 'timely' quarterly estimated tax payments), either 100% of your tax liability for 2023 (110% if AGI > 150k), or 90% of your tax liability for 2024, whichever is smaller. This is the 'safe harbor' amount, so you should be able to calculate what that is for your situation. The actual penalty is based on how much you underpaid vs. the safe harbor amount (not your final tax dues) and is divided up and calculated quarterly so if you were $1000 under the safe harbor it's calculated as underpaid $250 since Q1, $500 since Q2, $750 since Q3, $1000 since Q4 - at an underpayment penalty rate of 8% the math works out to be about $50 penalty in that example.
If you are on TT Desktop in Forms mode you can double-click on the penalty on your form 1040 and again on the 1040 worksheet to bring up Form 2210 which shows the calculations. This may also be in your PDF with "all forms and worksheets". You can also check under Other Tax Situations / Underpayment Penalty to make sure for example that TT has the correct 2023 tax figures for this calculation. This is also where you can adopt the "Annualized Income" method which is useful if you have some large unexpected income event (e.g. ROTH conversion in Q4) and need to make estimated tax payments unevenly - but this can be a lot of extra work and best avoided.
If you had a penalty for 2024 and didn't have any one-off income event or pay estimated tax usually then your withholding may need adjusting, or you may need to be paying estimated taxes in 2025, the deadline for Q1 ES payment is 4/15. You can work thru this in TT under Other Tax Situations / Form W4 and Estimated Taxes, where you can also provide estimates for 2025 to see if the "90% of 2025 tax" is smaller than "100% of 2024 tax" and figure out if your withholding is enough or ES is required. By default TT will generate ES vouchers based on "100% of 2024 tax" and assumes your 2025 withholding will be the same as 2024, unless you provide 2025 estimates via the interview process.
Your state likely follows similar process.
Once you figure out the 'safe harbor' for your situation and keep that in mind, it gets easier to figure out what is going on with penalties and withholding/estimated taxes for 2024 filing and 2025 planning.
