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Quarterly Estimated Tax Estimator

Divide projected unpaid tax across the estimated-tax installments that remain. The page starts with annual tax, subtracts withholding and refundable credits, then accounts for payments already made.

An optional safe-harbor target can be entered when you have separately determined an applicable threshold. Safe-harbor rules and due dates vary, so the calculator does not invent a threshold from income alone.

Enter your assumptions

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Result
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Estimated result
Projected unpaid tax—
Payment target used—
Remaining estimated payments—
Per remaining installment—

1. Use one tax period
Enter all income, deductions, payments, and rates for the same tax year or modeled period.

2. Enter the source amounts
Use records or a prepared estimate rather than mixing gross and net figures.

3. Apply the correct treatment
Choose rates and deductions that match the jurisdiction, taxpayer, asset, or entity being modeled.

4. Review the breakdown
Check intermediate values for duplicated deductions, missing payments, or an unintended zero result.

5. Test another scenario
Change one assumption at a time to see which input drives the estimate; use Reset to restore defaults.

Projected unpaid tax = max(0, Annual tax − Withholding − Refundable credits) Payment target = Projected unpaid tax, or the lower optional safe-harbor target Payment per remaining installment = max(0, Payment target − Payments made) ÷ Installments remaining

What the result means

The displayed result applies only to the assumptions entered and the simplified calculation shown above.

This is a planning estimate, not tax advice. Tax rules vary by jurisdiction, entity type, filing status, holding period, deductions, credits, and tax year.

Given: Annual tax of $24,000, expected withholding of $6,000, $4,500 already paid, and three installments left.

Calculation: Unpaid tax = $24,000 − $6,000 = $18,000. Remaining target = $18,000 − $4,500 = $13,500. Installment = $13,500 ÷ 3 = $4,500.

Result: The equal-payment estimate is $4,500 for each remaining installment.

Are quarterly periods exactly three months each?

Not always. Some systems use payment periods with uneven date ranges, so verify the official due dates.

What is a safe-harbor target?

It is an amount determined under applicable rules that may reduce underpayment-penalty exposure. Calculate it from official instructions before entering it.

What if income is seasonal?

Equal installments may be inappropriate. An annualized-income method may better match tax to when income was earned.

Should self-employment tax be included?

Include it in projected annual tax if the payment is intended to cover both income tax and self-employment tax.

Can withholding replace estimated payments?

Often withholding and estimated payments both count toward tax paid, but timing and penalty treatment can differ by jurisdiction.