Freelance income isn't withheld as it's earned, so the IRS expects four payments across the year instead of one in April. This splits a known tax total into that schedule.
Your inputs
Expected total tax owed this year$18,000
Combine your expected income tax and self-employment tax for the year.
Q1 — due Apr 15$4,500
Q2 — due Jun 15$4,500
Q3 — due Sep 15$4,500
Q4 — due Jan 15 (next year)$4,500
Per-quarter payment
$4,500
Equal split across 4 payments
Per month, if saving ahead
$1,500
Payments per year
4
This splits a known total evenly — it doesn't calculate the total itself, use the Self-Employment Tax tool alongside your expected income tax for that figure. To avoid a penalty, the IRS generally expects at least 90% of this year's bill, or 100–110% of last year's, paid through the year (the "safe harbor" rule).