first determine your 'safe harbor' and amount of tax you need to pay (100% of your 2024 tax [110% if 2024 AGI > 150k or 75k if Married Filing Separately, or 90% of 2025 tax - whichever is smaller) - refer to https://www.irs.gov/forms-pubs/about-form-1040-es for more info and worksheets. See also Form 2210 lines 1-9 (link below).
Note - if you are behind on ES for 2025 then pay the Q1+2 payments ASAP to stop the penalty from accruing at 8% annual rate, then resume quarterly payments for Q3/4 by the Sep/Jan deadlines. You can also err on overpaying Q1/2 and adjust lower later in the year if your 2025 estimate improves; overpayment will carry forward to later quarters, but overpayment in later quarters will not address underpayment earlier.
If your situation is clear-cut enough to make paying ES based on 2024 tax more advantageous, then that is known and a simpler calculation; you don't need to worry about timing and estimating 2025 but keep handle on 2025 situation to set aside tax for your final payment in April 2026.
TT has some tax calculators https://turbotax.intuit.com/tax-tools/ - can't speak to them in detail but I don't think have been updated for 2025 / big bill changes yet. But still useful to get in the ballpark; or see what other online tax calculators are available; if you have TT desktop you can run a dummy return for your 2025 tax using the 2024 software (and play around with different ES penalty situations, Form 2210 etc) especially given the SE component, and tweak the outcome for different tax brackets/deductibles if material. It depends the extent to which you are affected by the changes, see https://turbotax.intuit.com/tax-tips/general/taxes-2021-7-upcoming-tax-law-changes/L3xFucBvV?cid=em_...
When you file your return, TT will generate ES vouchers (which you don't need to use) for next year based on prior year tax from that return and assuming withholding will be the same. You can provide estimates for the next year under Other Tax Situations / Form W4 and Estimated Taxes and TT will then optimize the quarterly ES using the safe harbor calculation. So you can do some planning for the next year at the time you file in April, to make the Q1 ES payment on time.
If your income is uneven and in particular backloaded (e.g. Roth conversion in Q4) you may be able to reduce the penalty by using Form 2210 Annualized Income method, but you will need to calculate a quarterly AGI/withholding/qualdivs/LTCG for 3/31, 5/31, 8/31 as well as full year return for 12/31 figures, when you file for 2025. If your income is actually even then the AI method will not rescue you from a penalty for ES payments which were actually due in earlier quarters but are simply late. It may help you a bit if your 1099 income is on a lag. You can see more in Form 2210 which also contains the default safe harbor calculation on lines 1-9
https://www.irs.gov/pub/irs-pdf/i2210.pdf
To make payments try to pay directly at irs.gov rather than checks and vouchers, the less mailed to IRS the better. You can also see record of all your payments online in your IRS account.
Don't forget state ES and penalties also.
Not a CPA, please research accordingly - hope this helps.
