Estimated Quarterly Tax Calculator Formula
Understand the math behind the estimated quarterly tax calculator. Each variable explained with a worked example.
Formulas Used
Quarterly Payment
quarterly_payment = (federal_tax + se_tax + taxable * state_rate / 100) / 4Annual Tax Estimate
annual_total = federal_tax + se_tax + taxable * state_rate / 100Effective Total Rate
effective_rate = annual_income > 0 ? (federal_tax + se_tax + taxable * state_rate / 100) / annual_income * 100 : 0Variables
| Variable | Description | Default |
|---|---|---|
annual_income | Expected Annual Income(USD) | 100000 |
deductions | Estimated Deductions(USD) | 20000 |
state_rate | State Tax Rate(%) | 5 |
taxable | Derived value= max(annual_income - deductions, 0) | calculated |
se_tax | Derived value= annual_income * 0.9235 * 0.153 | calculated |
federal_tax | Derived value= taxable <= 11600 ? taxable * 0.10 : (taxable <= 47150 ? 1160 + (taxable - 11600) * 0.12 : (taxable <= 100525 ? 5426 + (taxable - 47150) * 0.22 : 17168.5 + (taxable - 100525) * 0.24)) | calculated |
How It Works
Estimated Quarterly Tax Payments
Quarterly = (Federal Tax + SE Tax + State Tax) / 4
Due dates: April 15, June 15, September 15, January 15
You must make estimated payments if you expect to owe $1,000 or more in taxes for the year.
Worked Example
$100,000 income, $20,000 deductions, 5% state rate.
- 01Taxable = $80,000
- 02Federal tax on $80k = ~$12,660
- 03SE tax = $100k x 0.9235 x 15.3% = $14,130
- 04State tax = $80k x 5% = $4,000
- 05Total = ~$30,790, Quarterly = ~$7,698
Frequently Asked Questions
When are quarterly taxes due?
Q1: April 15, Q2: June 15, Q3: September 15, Q4: January 15 of the following year. If a due date falls on a weekend or holiday, it moves to the next business day.
What happens if I underpay?
The IRS charges an underpayment penalty (currently ~8% annual rate). To avoid penalties, pay at least 90% of current year tax or 100% of prior year tax (110% if AGI > $150,000).
Can I pay through withholding instead?
Yes. If you have a spouse with W-2 income, you can increase their withholding to cover your self-employment tax, eliminating the need for quarterly payments.
Ready to run the numbers?
Open Estimated Quarterly Tax Calculator