Comprehensive Guide
Learn more in our Business & Tax Guide.
How it works
When no employer withholds tax for you, the IRS expects you to pay as you go, in four quarterly instalments — and this calculator estimates each one. It starts with the part salaried people never see: self-employment tax, the 15.3% that covers both halves of Social Security and Medicare, charged on 92.35% of your net profit. Half of that is then deductible, and the rest of your profit, minus the standard deduction, flows through the federal income-tax brackets. Add the two and divide by four. On $80,000 of profit as a single filer, the self-employment tax alone is roughly $11,300, the income tax adds several thousand more, and the quarterly payment lands near $3,700. The figure is a planning estimate, not a filing number — state tax, credits and itemised deductions are left out, and the brackets are approximate 2026 values. The practical safeguard is the safe-harbour rule: pay 100% of last year's total tax (110% if you earned over $150,000) in four equal instalments and you avoid the underpayment penalty even if this year's bill comes in higher. Note the quarters are not evenly spaced — payments fall due mid-April, mid-June, mid-September and mid-January.Formula
SE tax = profit x 92.35% x 15.3% | income tax on (profit + other - half SE tax - standard deduction)
Tips
- Self-employment tax is 15.3% on 92.35% of net profit — the part salaried people never see.
- Safe harbour: pay 100% of last year's tax (110% over $150k) to avoid the penalty.
- The four quarters are uneven — April, June, September, January.
- Set aside a fixed share of every payment you receive so the quarter never hurts.
- State tax and credits are excluded — treat this as a planning floor, not the bill.
Frequently asked questions
How much should I pay in quarterly estimated taxes?
Add your self-employment tax (15.3% on 92.35% of net profit) to your income tax, and divide by four. On $80,000 of profit a single filer owes roughly $3,700 a quarter. The calculator estimates it; safe harbour lets you base it on last year's bill instead.
What is self-employment tax?
The 15.3% that funds Social Security and Medicare for the self-employed — both the employee and employer halves a salaried person splits with their company. It is charged on 92.35% of net self-employment profit, and half of it is deductible against income tax.
What is the safe harbour rule for estimated tax?
Pay 100% of last year's total tax — 110% if your income topped $150,000 — across four equal instalments, and you avoid the underpayment penalty even if this year's bill turns out higher. It is the simplest way to stay safe when income is unpredictable.
When are quarterly estimated taxes due?
Mid-April, mid-June, mid-September and mid-January — note the quarters are not evenly spaced. Missing a deadline triggers an underpayment penalty calculated on what you should have paid by that date.
Do I need to pay quarterly taxes on side income?
If you expect to owe $1,000 or more at filing after withholding and credits, generally yes. A day job's withholding can cover a small side hustle, but a meaningful one usually needs quarterly payments or extra withholding to avoid a penalty.