How do I calculate quarterly estimated tax?

Six steps, no tax background needed: start with quarterly net profit, compute self-employment tax (15.3 percent of 92.35 percent of net earnings), subtract half the SE tax and the standard deduction, apply the 2026 federal brackets, then divide the total federal tax by four. A single filer netting $25,000 a quarter owes about $6,436 per quarter.

What is the estimated tax safe harbor rule?

The safe harbor switches the IRS underpayment penalty off. Pay at least 90 percent of this year's total tax, or 100 percent of last year's total tax, 110 percent if last year's adjusted gross income topped $150,000, spread across the four quarterly payments.

When are 2026 estimated tax payments due?

April 15, June 15, and September 15, 2026, then January 15, 2027. Two quirks: the IRS's 'quarters' are not calendar quarters, the June payment covers only April and May, and the final payment lands in the next calendar year.

Why does 'just set aside 30%' fail for freelancers?

It fails in both directions. On $25,000 a quarter, 30 percent says $7,500, about $1,064 more than the real $6,436, leaving roughly $4,250 a year sitting idle. At lower incomes it can undershoot, since the self-employment tax alone is 14.1 percent of every net dollar before income tax even starts.

Taxes, without the panic

Quarterly Estimated Tax Calculator: What Should You Set Aside?

KOLLAZ · Updated October 1, 2026

Four glass jars filled with gold coins on a windowsill, the window behind them showing the four seasons

The short answer

Quarterly estimated tax calculator: what should you set aside? Safe-harbor math for freelancers, with IRS due dates and penalty traps.

Updated September 2026. This article is for educational purposes only and is not tax advice. Confirm current figures at irs.gov or with a tax professional.

A freelancer lands a $25,000 quarter. The money hits the account, the client is happy, and then the real question arrives: how much of that $25,000 actually belongs to the IRS? That is the question a quarterly estimated tax calculator answers, not with a folk rule like “set aside 30%,” but with the real 2026 math: actual tax brackets, the actual standard deduction, and the 15.3% self-employment tax that blindsides most new freelancers.

The short answer: on $100,000 of annual freelance profit, $25,000 a quarter, a single filer taking the standard deduction owes about $25,745 in federal tax for 2026. That's $6,436 to set aside per quarter, roughly 25.7% of each payment. Below is how that number is built, step by step, so you can run the same math on your own income.

How does a quarterly estimated tax calculator work?

Six steps. No tax background needed:

Start with quarterly net profit. Revenue minus deductible business expenses. For the annual math, use your projected full-year profit, here, $100,000.
Compute self-employment tax. Take 15.3% of 92.35% of net earnings. On $100,000: $100,000 × 0.9235 = $92,350, and 15.3% of that is $14,129.55. This is the tax W-2 workers never see, because their employer quietly pays half of it.
Subtract half the SE tax and the standard deduction. Half of $14,129.55 ($7,064.78) is deductible when figuring income tax, and the 2026 standard deduction for a single filer is $16,100. Taxable income: $100,000 − $7,064.78 − $16,100 = $76,835.22.
Run the 2026 brackets. Income is taxed in slices: 10% on the first $12,400, 12% on the slice up to $50,400, 22% on the rest. On $76,835.22, that works out to $11,615.75.
Add the two taxes together. $14,129.55 + $11,615.75 = $25,745.30 in total federal tax.
Split by quarter and check the safe harbor. Each quarter's share follows its income: $25,745.30 × ($25,000 ÷ $100,000) = $6,436.33 per quarter. Then confirm every quarter clears the safe-harbor floor, so no underpayment penalty applies.

What does a worked example show for a single filer with $25,000 a quarter?

Putting the steps together for a single filer netting $25,000 each quarter:

Annual net profit: $100,000
Self-employment tax: $14,129.55
One-half SE deduction: $7,064.78
Standard deduction (single, 2026): $16,100
Taxable income: $76,835.22
Federal income tax (2026 brackets): $11,615.75
Total federal tax: $25,745.30
Set aside per quarter: $6,436.33
Safe to spend per quarter: $18,563.67
Effective tax rate: 25.7%

The safe-harbor check: 90% of this year's tax, divided by four, is $5,792.69 a quarter. The $6,436.33 set-aside clears it comfortably, no penalty, even if December brings a surprise bonus quarter.

I built the Quarterly Tax Set-Aside Calculator to run exactly this math: type in each quarter's income and filing status, and it returns the per-quarter set-aside, the safe-to-spend remainder, a live countdown to every 2026 IRS deadline, and the safe-harbor check, all from the real 2026 IRS figures. It is an Excel spreadsheet with no macros, US$8.99, and it does one job.

What is the safe-harbor rule, your penalty off-switch?

The IRS doesn't just want its money in April, it wants it during the year, and it charges an underpayment penalty when you fall short, even if you pay in full at filing time. The safe harbor switches that penalty off. Pay at least 90% of this year's total tax, or 100% of last year's total tax, 110% if last year's adjusted gross income topped $150,000, spread across the four quarters, and the penalty can't touch you. There is also a $1,000 floor: owe less than $1,000 when you file and no penalty applies. For the full walkthrough with every due date, see our guide to freelancer quarterly taxes for 2026.

When are the 2026 estimated payments due?

April 15, June 15, and September 15, 2026, then January 15, 2027. Two quirks: the IRS's “quarters” aren't calendar quarters, the June payment covers only April and May, and the final payment lands in the next calendar year. This article was updated in September 2026, so the September 15 payment just passed. Missed it? Pay now. The IRS judges each payment period on its own, so catching up stops additional penalty from building. One payment remains: January 15, 2027.

Why does the flat 30% guess fail?

“Just set aside 30%” is the most repeated advice freelancers get, and it fails in both directions. On $25,000 a quarter, 30% says $7,500, that's $1,064 more than the real $6,436, or about $4,250 a year sitting idle instead of earning or being spent. And at lower incomes the guess can undershoot: the self-employment tax alone is 14.1% of every net dollar before income tax even starts. A flat percentage can't know your bracket, your filing status, or your deduction. The 2026 brackets can, they're public, and the arithmetic takes about a minute. If your rates feel like guesswork from the other direction, run the numbers on what you should actually charge as a freelancer, the set-aside only works if the income it's carved from is priced right.

About Kollaz, Kollaz makes smart financial tools for modern money. This article's companion is the Quarterly Tax Set-Aside Calculator spreadsheet: turn each quarter's freelance income into a set-aside dollar amount, a safe-to-spend remainder, and a live countdown to every 2026 IRS deadline.

Sources

Internal Revenue Service: Estimated Tax, Individuals (FAQ) (opened and read September 2026): $1,000 payment threshold; 90%-of-current-year / 100%-of-prior-year (110% over $150,000 AGI) safe harbor; the four payment periods and their due dates.
Internal Revenue Service: Self-Employment Tax (Social Security and Medicare Taxes) (opened and read September 2026): 15.3% rate (12.4% Social Security + 2.9% Medicare); employer-equivalent half deductible for income tax; SE tax payable through quarterly estimated payments.
Internal Revenue Service: Estimated Taxes (topic page) (opened and read September 2026): who must pay estimated tax and how quarterly payments work.
bestmoney.com: Standard Deduction 2026: Amounts, Rules & How to Claim It (opened and read September 2026; secondary source): 2026 standard deduction $16,100 single / $32,200 married filing jointly, per IRS release IR-2025-103.

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