Why freelancers set aside a percentage, not a guess
Employees never see the system that protects them: tax is skimmed from every paycheck before it arrives. Freelancers get the whole payment and the whole responsibility, which is how a good year turns into a bad April. The fix used by experienced independents is boring and effective — decide on a set-aside percentage, and move that share of every payment into a separate tax account the day it lands. This calculator works out what that percentage should be for your numbers, instead of the flat guesses (15%? 30%?) that are usually wrong in one direction or the other.
Two taxes are being estimated. Self-employment tax is 15.3% applied to 92.35% of your net profit — it covers the Social Security and Medicare shares that an employer would normally split with you. Half of it is deductible, which the calculator accounts for before computing federal income tax using 2025 brackets and the standard deduction for your filing status. State tax is modeled the simple way, as a flat percentage of taxable income, because fifty different state systems cannot be one honest field. The total is then divided by four to give the quarterly estimated payment, the amount the IRS expects in April, June, September and January.
Two habits make the estimate hold up. First, keep business expenses current — every legitimate expense lowers net profit, which lowers both taxes, so a shoebox of unlogged receipts is literally money left on the table. Second, re-run the estimate when income changes materially; a percentage set in a $60,000 year under-collects in a $110,000 year because brackets rise with income. Treat the result as a planning floor, keep the set-aside account untouched, and let any surplus be a pleasant refund to yourself at filing time.