Why quarterly taxes matter
The US tax system is "pay as you go." When you have a regular paycheck, your employer withholds federal tax from each one. When you are self-employed, no one does that for you — so the IRS expects you to send an estimated payment four times a year. Skip those payments and you owe interest on what should have been paid, even if you settle the full bill on April 15.
The two safe harbors, explained
The IRS will not charge an underpayment penalty if your quarterly payments add up to the lesser of:
- 90% of the current year's total tax. Hard to know mid-year because you have to estimate it. The calculator projects from your YTD pace.
- 100% of last year's total tax (or 110% if your prior-year AGI was over $150,000 single / $75,000 MFS). This one is easy because last year's number is final and printed on line 24 of your 1040.
Most people pick the prior-year safe harbor when income is climbing — it locks in a fixed target, you cannot underpay against an unknown future. The calculator shows both numbers and uses the smaller one automatically.
2026 quarterly deadlines
- Q1 (income earned Jan–Mar): due April 15, 2026
- Q2 (income earned Apr–May): due June 15, 2026
- Q3 (income earned Jun–Aug): due September 15, 2026
- Q4 (income earned Sep–Dec): due January 15, 2027
Note that the "quarters" are not even — Q2 covers only April and May. That uneven spacing trips up first-time filers; mark the dates in your calendar and forget the math. The estimator above also lets you switch to the 2025 or 2024 calendar from the year selector if you need to.
How to actually pay
The cleanest method is IRS Direct Pay at irs.gov/payments — free, no account needed, takes about five minutes. You can also mail a check with Form 1040-ES (slower, more error-prone) or use EFTPS if you are already enrolled. Save the confirmation number for your records.
How to use the estimator
- Add up your year-to-date income. Total all 1099 / freelance income received from January 1 through today. Include cash, Venmo, Stripe, Etsy payouts. Be honest with yourself; underestimating means a surprise bill in April.
- Subtract year-to-date business expenses. Software, equipment, mileage, home office portion, contractors, marketing — anything you would deduct on Schedule C.
- Pick the quarter you are paying for. Q1 (Jan–Mar, due April 15), Q2 (Apr–May, due June 15), Q3 (Jun–Aug, due Sep 15), Q4 (Sep–Dec, due Jan 15 of next year).
- Enter what you already paid. Sum of every estimated tax check you sent earlier this year, plus any federal withholding from W-2 paychecks if you also have a regular job.
- Enter last year's total tax. Line 24 of your prior 1040. The estimator uses this for the prior-year safe harbor (100% or 110%).
- Read the recommended payment. The estimator picks the cheaper of the two safe harbors and tells you exactly what to send before this quarter's deadline. Pay it on IRS Direct Pay and you are out of penalty zone.
FAQ
Who has to pay quarterly estimated taxes?
Anyone who expects to owe at least $1,000 in tax after subtracting withholding. That covers most freelancers, gig workers, sole proprietors, and partners. Corporations have a different $500 threshold.
When are the quarterly tax deadlines?
2026: April 15 (Q1), June 15 (Q2), September 15 (Q3), and January 15, 2027 (Q4). 2025: April 15, June 16 (June 15 was a Sunday), September 15, and January 15, 2026. When any deadline falls on a weekend or federal holiday it shifts to the next business day.
What is the IRS safe harbor for estimated taxes?
The IRS will not charge an underpayment penalty if you pay (in roughly equal quarterly installments) the lesser of: (1) 90% of the current year's tax, or (2) 100% of last year's total tax. If your AGI was over $150,000 (or $75,000 married filing separately), the second option becomes 110% instead of 100%.
How does this calculator decide what I owe?
It projects your full-year income from your year-to-date pace, runs that projection through the tax engine to estimate annual tax, applies both safe-harbor rules, picks the lower of the two as your target, multiplies by the fraction of the year through the selected quarter, then subtracts what you have already paid in withholding and prior estimates.
What if my income is lumpy — big spikes some months?
The "regular installment method" used here divides the annual estimate into 4 equal payments. If your income arrives unevenly (e.g. nothing in Q1 then $80k in Q3), the IRS lets you use the annualized-income method on Form 2210 to lower earlier-quarter requirements. That is its own tool — out of scope for this estimator.
How do I actually send a quarterly payment?
Use IRS Direct Pay (free, takes 5 minutes) at irs.gov/payments, or mail a check with Form 1040-ES. Some states require their own quarterly payments separately; check your state's revenue department.
What happens if I underpay?
The IRS charges interest on the underpaid amount, calculated quarter by quarter. The rate is the federal short-term rate plus 3 percentage points and is updated each quarter — historically it has hovered in the 7–8% annualized range. It is smaller than filing penalties but adds up across the year, so it pays to estimate accurately.
Does this include state quarterly taxes?
No. Each state has different rules and rates; many (Florida, Texas, Washington, Tennessee, etc.) have no state income tax. Add your state liability separately when planning what to send each quarter.