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.