Quarterly Estimated Tax Calculator for Self-Employed Contractors (2026)

Quarterly estimated tax is the federal income and self-employment tax you prepay four times a year when no employer withholds it. For 2026, pay the smaller of 90% of this year's tax or 100% of last year's (110% if last year's AGI topped $150,000), split across April 15, 2026, June 15, 2026, Sept. 15, 2026 and Jan. 15, 2027.

How do you calculate quarterly estimated taxes?

Estimate this year's total federal tax, compare 90% of it with 100% (or 110%) of last year's total tax, take the smaller number, subtract any withholding, and divide by four. That's the method on the 2026 Form 1040-ES worksheet, and it's what the calculator does.

Payment per quarter = (min(90% × T₍this year₎, P × T₍last year₎) − W) ÷ 4

1. 1

   Project your net profit for the year.

   Take revenue minus business expenses so far, then scale it to twelve months. If your work is seasonal, use last year's month-by-month split instead of a straight line.

2. 2

   Figure self-employment tax.

   Multiply profit by 92.35%, then by 15.3% (12.4% Social Security up to the $184,500 wage base, plus 2.9% Medicare). Half of it is deductible. The self-employment tax calculator breaks this out.

3. 3

   Figure income tax.

   Subtract half of SE tax and the 2026 standard deduction ($16,100 single, $32,200 married filing jointly), take the 20% QBI deduction if you qualify, and run the rest through the 2026 brackets.

4. 4

   Pick your safe harbor.

   Compare 90% of that total with 100% or 110% of last year's tax. The smaller number is the least you can prepay without an underpayment penalty.

5. 5

   Pay a quarter by each due date.

   Pay through IRS Direct Pay, EFTPS or your IRS online account by April 15, 2026, June 15, 2026, Sept. 15, 2026, Jan. 15, 2027.

When are 2026 quarterly estimated taxes due?

For calendar-year taxpayers, the 2026 payments are due April 15, 2026, June 15, 2026, Sept. 15, 2026 and Jan. 15, 2027. The "quarters" aren't equal: the second payment comes only two months after the first. A payment mailed with a U.S. postmark on or before the due date counts as on time.

What is the safe harbor for estimated taxes?

The safe harbor is the smallest prepayment that keeps you clear of the IRS underpayment penalty: 90% of this year's tax or 100% of last year's, whichever is less. If your 2025 adjusted gross income was over $150,000 ($75,000 married filing separately), the prior-year number is 110%. Your 2025 return must cover a full 12 months.

• Prior-year safe harbor is the one most owners use. It's a fixed number you know in April, so a big year can't surprise you with a penalty. You still owe the difference when you file.
• Current-year safe harbor (90%) saves cash when this year is slower than last, but it only works if your estimate holds up. Recheck it every quarter.
• High-income rule. With the same $120,000 profit, an owner whose 2025 AGI was $160,000 and tax was $30,000 would have a 110% target of $33,000. That's higher than 90% of this year ($25,616), so the 90% route wins at $6,404 a quarter.
• No tax last year. If you were a U.S. citizen or resident for all of 2025 and had no tax liability for that full year, you generally don't have to pay 2026 estimated tax.

How much should a contractor set aside for taxes?

A useful habit is to move a fixed share of every customer payment into a separate tax account. The calculator's "share of profit to set aside" shows your number; in the example it's 24% of profit for federal tax alone. Add your state's rate on top. See how much to set aside for taxes for a fuller walkthrough.

What happens if you miss or underpay a quarter?

The IRS charges an underpayment penalty figured like interest, for each quarter, from the due date until the shortfall is paid. Paying a missed quarter late still cuts the penalty, so pay as soon as you can rather than waiting for April. You may be able to reduce it with the annualized method if your income was uneven.

Common mistakes

• Forgetting self-employment tax. Income tax alone understates what a sole proprietor owes, often by thousands.
• Using revenue instead of profit. Estimated tax is figured on net profit after business expenses, not on what customers paid you.
• Spending the tax money. Cash in the operating account looks like profit until June 15 shows up.
• Skipping state estimates. Most income-tax states have their own quarterly schedule. See your state in our state tax guides.
• Messy books. If expenses aren't categorized monthly, you can't project profit, so every estimate is a guess. A monthly bookkeeping checklist fixes that.