The most common freelancer money mistake isn't undercharging — it's spending money that already belongs to the IRS. Here's the simple version of quarterly tax math for US freelancers.
The two taxes you owe
Self-employment tax: 15.3% (Social Security + Medicare), applied to 92.35% of your net profit — that's the Schedule SE method. Income tax: your regular bracket rate on profit after deductions.
A worked example
Say you collected $6,000 this quarter and had $800 in deductible expenses. Net profit: $5,200. Self-employment tax: $5,200 × 92.35% × 15.3% ≈ $735. Income tax at an effective 15%: $780. Total to set aside: about $1,515 — roughly 29% of profit.
The system that works
Track paid invoices and expenses as they happen, compute the set-aside quarterly, and move that money to a separate account the day you run the numbers. Estimated payments are due mid-April, June, September, and January.
Our Freelancer Finance Pack ($19) does this automatically — income tracker, expense log, and a quarterly tax estimator using exactly this math, plus a ready-to-send invoice template. Code LAUNCH20 = 20% off. (Estimates, not tax advice — confirm with a professional.)