A common rule of thumb is 25–30% of your net self-employment income, but the real number depends on your total income and filing status. The calculator above uses 2026 IRS numbers to combine self-employment tax (15.3% on 92.35% of net profit, Social Security capped at $176,100) with federal income tax after the standard deduction, the deductible half of SE tax, and a rough 20% QBI deduction — then divides by 12 for a monthly set-aside.
Self-employment tax is the Social Security and Medicare tax (15.3% total) that a W-2 employer normally splits with you. When you're self-employed you pay both halves yourself on 92.35% of your net profit. It's on top of regular federal income tax — which is why setting aside only for income tax leaves most 1099 workers short.
No — the IRS collects through quarterly estimated payments (April, June, September, January), not monthly. Setting money aside every month is just the easiest way to always have the quarterly payment ready. The calculator shows both the monthly amount to save and the quarterly amount to send.