What is the estimated quarterly tax calculator?
In short
Self-employed taxpayers must pay estimated taxes quarterly. On $90,000 of income with $15,000 in expenses, net income is $75,000 — about $10,600 in self-employment tax plus $9,000 in income tax (12%), so roughly $4,900 per quarter. The safe-harbor amount (based on last year's tax) avoids penalties.
Estimates your annual self-employment and income tax, divides it into quarterly payments, and computes the safe-harbor amount that protects you from underpayment penalties.
How to use this calculator
- 1Enter your expected annual self-employment income and business expenses.
- 2Set your income tax rate (separate from self-employment tax).
- 3Enter last year's total tax for the safe-harbor calculation.
- 4See your quarterly payment and the penalty-proof safe-harbor amount.
The formula
- netSE
- — Net income = income − expenses
- SE tax
- — 12.4% Social Security (up to the wage base) + 2.9% Medicare, on netSE × 92.35%
- income tax
- — netSE × rate
- quarterly
- — (SE tax + income tax) / 4
Worked example
The scenario
$90,000 income, $15,000 expenses, 12% income tax rate, $14,000 last-year tax.
The result
Net income: $75,000. Annual tax: ~$19,600. Quarterly: ~$4,900. Safe-harbor: ~$3,500/quarter — the lesser of 90% of this year’s tax or 100% of last year’s $14,000.
Common use cases
- Freelancers and independent contractors paying quarterly estimated taxes.
- Side-hustlers who owe more than $1,000 in tax beyond withholding.
- Avoiding IRS underpayment penalties via the safe-harbor rule.
Limitations & assumptions
- Uses a flat income tax rate rather than graduated brackets.
- Does not account for the deductible half of self-employment tax or QBI deduction.
- Does not include state estimated taxes, which may also be due quarterly.
- Divides the annual estimate into four equal payments. If your income is uneven or seasonal, the annualized income installment method (Form 2210, Schedule AI) can legitimately lower early-quarter payments — this calculator does not model it.
- The 110% safe-harbor tier applies above $150,000 of prior-year AGI ($75,000 if married filing separately — this filing status is not modeled here).
- Does not model the 0.9% Additional Medicare surtax on self-employment earnings above $200,000 ($250,000 married filing jointly) — thresholds depend on filing status.
Frequently asked questions
Who has to pay quarterly estimated taxes?
When are quarterly taxes due?
What is the safe harbor rule?
What happens if I underpay?
Does this include self-employment tax?
Disclaimer: KalkWise calculators are provided for general informational and educational purposes only and do not constitute financial, investment, tax, or legal advice. Results are estimates based on the figures you enter and the assumptions described above. Actual outcomes will vary. Consult a qualified professional before making financial decisions.