Quarterly Estimated Tax Calculator — Rex's Toolbox

Rex says

Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.

Try a scenario

Click to load — tweak from there.

Inputs

Projected self-employment net profit($)

Other income (W-2, interest, rent)($)

Tax already withheld this year($)

Standard or itemised deduction($)

Effective federal income tax rate(%)

Total tax on last year's return($)

Last year's AGI($)

Social Security wage base($)

Result

Send each quarter

$4,000

Total estimated payments required

$16,000

Projected total tax

$20,969

Self-employment tax

$12,010

Federal income tax

$8,959

Likely balance due at filing

$4,969

Safe harbor percentage applied

100%

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How to use this

1Enter projected self-employment net profit ($).
2Enter other income (w-2, interest, rent) ($).
3Enter tax already withheld this year ($).
4Enter standard or itemised deduction ($).
5Enter effective federal income tax rate (%).
6Enter total tax on last year's return ($).
7Enter last year's agi ($).
8Enter social security wage base ($).
9Read your send each quarter on the right — it updates as you type.
10Hit Share to keep the scenario or send it to someone.

About this calculator

Anyone with income that is not subject to withholding — freelancers, landlords, creators, investors, S-corp owners taking distributions — has to pay tax as they earn it or face an underpayment penalty computed as interest on each missed instalment. The practical target is not a perfect forecast, it is a safe harbor: pay at least 90% of this year's tax or 100% of last year's tax (110% if your prior-year adjusted gross income exceeded $150,000) and the penalty disappears even if you owe a large balance in April. This calculator estimates income tax and self-employment tax on your projected net earnings, subtracts withholding from any W-2 job, applies both safe harbor tests, and reports the smaller required amount split into the four instalments the IRS expects. It also shows the balance likely due at filing so you can decide whether to overpay slightly for comfort. State estimates are separate and often on different dates — check your state's schedule.

FormulaRequired = min(90% × Current-Year Tax, Safe Harbor % × Prior-Year Tax) − Withholding. Quarterly = Required ÷ 4.

Worked example

Using the values the calculator loads with:

Inputs

Projected self-employment net profit: 85000 $
Other income (W-2, interest, rent): 0 $
Tax already withheld this year: 0 $
Standard or itemised deduction: 15000 $
Effective federal income tax rate: 14 %
Total tax on last year's return: 16000 $
Last year's AGI: 120000 $
Social Security wage base: 176100 $

Results

Send each quarter: $4,000
Total estimated payments required: $16,000
Projected total tax: $20,969
Self-employment tax: $12,010
Federal income tax: $8,959
Likely balance due at filing: $4,969
Safe harbor percentage applied: 100%

What each field means

Inputs

Projected self-employment net profit ($): The projected self-employment net profit used in the calculation, measured in $. Starts at 85000 $ so you have a working example on load. Accepted range: 0–2000000 $.
Other income (W-2, interest, rent) ($): The other income (w-2, interest, rent) used in the calculation, measured in $. Starts at 0 $ so you have a working example on load. Accepted range: 0–5000000 $.
Tax already withheld this year ($): The tax already withheld this year used in the calculation, measured in $. Starts at 0 $ so you have a working example on load. Accepted range: 0–500000 $.
Standard or itemised deduction ($): The standard or itemised deduction used in the calculation, measured in $. Starts at 15000 $ so you have a working example on load. Accepted range: 0–200000 $.
Effective federal income tax rate (%): The effective federal income tax rate used in the calculation, measured in %. Starts at 14 % so you have a working example on load. Accepted range: 0–40 %.
Total tax on last year's return ($): The total tax on last year's return used in the calculation, measured in $. Starts at 16000 $ so you have a working example on load. Accepted range: 0–1000000 $.
Last year's AGI ($): The last year's agi used in the calculation, measured in $. Starts at 120000 $ so you have a working example on load. Accepted range: 0–5000000 $.
Social Security wage base ($): The social security wage base used in the calculation, measured in $. Starts at 176100 $ so you have a working example on load. Accepted range: 100000–300000 $.

Results

Send each quarter: Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Total estimated payments required: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Projected total tax: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Self-employment tax: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Federal income tax: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Likely balance due at filing: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Safe harbor percentage applied: Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

When are the payments due?

For calendar-year taxpayers the federal instalments are generally due in mid-April, mid-June, mid-September, and mid-January of the following year. The periods are uneven, which is why the June payment covers only two months.

Can I just pay it all in the fourth quarter?

Not without a penalty. The underpayment penalty is calculated per period, so a large January payment does not cure missed April and June instalments unless you use the annualised income method on Form 2210.

What if my income is seasonal?

Use the annualised income instalment method, which lets you pay in proportion to when you actually earned the money. It requires more record-keeping but can eliminate penalties for a business with a lumpy year.

Is withholding better than estimates?

Often yes. Withholding is treated as paid evenly across the year regardless of when it happens, so increasing withholding late in the year through a W-2 job or a retirement distribution can retroactively fix an underpayment.

Accuracy and limitations

Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.

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Cite this calculator

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APA

RevenueLab. (2026). Quarterly Estimated Tax Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/quarterly-estimated-tax-calculator

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/quarterly-estimated-tax-calculator" target="_blank" rel="noopener">Quarterly Estimated Tax Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Quarterly Estimated Tax Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/quarterly-estimated-tax-calculator) (2026).