with all the tax law changes it will be hard to know what 90% of your 2025 tax will be. in addition, while your income will be lower and hence your income taxes will be lower but then you will have no withholding. you will also have self-employment tax which would be about 15% of your net se income.
a very rough way to estimate 100% of your 2025 tax would be to take your 2024 taxable income subtract out the taxable wages and add in your estimated se income. then use the 2024 tax rate schedule (see 1040 instructions page 109) to calculate income taxes to that add 15% of the SE income. There is no way to know how close this will be to your actual 2025 tax because of the need to estimate your se income for the whole year.
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
depending on what you estimate your 2025 tax to be (i'm ignoring the 90% rule) without withholding 75% needs to be paid in by the 3rd quarter
if you have penalties, you will be able to use the annualized income installment method to see if that reduces them.
