at best any calculator comes up with an estimate since you don't know what your taxable income for 2024 will be and then there are always changes in the tax laws.
there are safe harbors. using them you won't be subject to penalty but may have a big overpayment if income in 2024 drops or there's a major change in the tax laws.
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There will be no federal penalties for not paying in enough taxes during the year if withholding
1) and timely estimated tax payments equal or exceed 90% of your 2024 tax or
2) and timely estimated tax payments equal or exceed 100% of your 2023 tax (110% if your 2023 adjusted gross income was more than $150K) or
3) the balance due after subtracting taxes withheld from 90% of your 2024 tax is less than $1,000 or
4) your total taxes are less than $1,000
the lower of 1 or 2 is your required annual income tax payments. 1 is difficult to know until the year end so generally option 2 is the safer option. under the simplified method 25% of the estimated taxes must be paid in each quarter by 4/15, 6/15, 9/15 and 1/15/25. unless you can show otherwise 25% of your annual withholding is assumed to occur in each quarter.
failing this and being subject to penalties you can use the annualized installment income method.
this method requires knowing your income and deductions thru 3/31, then 5/31, then 8/31, and finally year end which should be the same as the tax return. the income is annualized. taxes are computed on the annualized income and then de-annualized. your tax payments for each period must equal or exceed these amounts to avoid penalties.
if you can increase withholding to meet any exceptions then paying the estimates is not required.
form 2210 page 3
https://www.irs.gov/pub/irs-pdf/f2210.pdf
state laws vary
