Who has to pay quarterly
If you're self-employed, a freelancer or a sole proprietor, nobody withholds tax from what you earn. The IRS expects you to pay during the year instead, in four payments, if you'll owe $1,000 or more when you file. Miss them and you pay a penalty, even if you pay everything in April.
Iowa
Iowa has a flat income tax of 3.8%, and the calculator works it out with Iowa's 2026 brackets, standard deduction and exemptions. Most states that tax income also want estimated payments; check Iowa's revenue department for its dates. Local income tax isn't included: School district income surtax (a % of state tax, typically 0-10%; average small).
What goes into the number
- Self-employment tax: 15.3% on 92.35% of your profit, for Social Security and Medicare. An employer would pay half of this for you; when you're self-employed you pay both halves.
- Federal income tax: on your profit after the standard deduction, half of your self-employment tax, and the 20% qualified business income deduction.
- State income tax, where your state has one.
The safe way to avoid a penalty
Pay at least 100% of last year's total tax (110% if your income was over $150,000) across the four payments, and there's no penalty even if you end up owing more. The calculator above estimates this year instead, which is closer to what you'll really owe.
When the payments are due
April 15, June 15, September 15, and January 15 of the next year. The periods aren't even quarters: the second covers only two months. When a date lands on a weekend or holiday, it moves to the next business day.