Estimated Tax Payment Periods: What Months Each Quarter Covers

October 2026

IRS estimated tax "quarters" are not calendar quarters. For individuals, the four payment periods cover January 1 – March 31 (due April 15), April 1 – May 31 (due June 15), June 1 – August 31 (due September 15) and September 1 – December 31 (due January 15 of the next year). So the September payment covers June through August, and September income belongs to the January payment.

Key Takeaways

The four IRS estimated tax periods are 3, 2, 3 and 4 months long, not 3 months each.
"Q3" for estimated taxes means June 1 – August 31, paid by September 15. It is not July – September.
When a due date lands on a weekend or legal holiday, it moves to the next business day.
Corporations, private foundations and fiscal-year filers use a different schedule.
With the regular method you pay a quarter of your annual target each time. Which months income falls in only changes the math if you use the annualized method.

What Months Does Each Estimated Tax Payment Cover?

This is the schedule for individuals, sole proprietors, single-member LLC owners, partners and S corporation shareholders who file on a calendar year:

Payment	Income Period	Length	Usual Due Date	For Tax Year 2026
1st (Q1)	January 1 – March 31	3 months	April 15	April 15, 2026
2nd (Q2)	April 1 – May 31	2 months	June 15	June 15, 2026
3rd (Q3)	June 1 – August 31	3 months	September 15	September 15, 2026
4th (Q4)	September 1 – December 31	4 months	January 15 (next year)	January 15, 2027

If a due date falls on a Saturday, Sunday or legal holiday, the payment is on time if it's made the next business day. You can also skip the January payment if you file your return and pay the full balance by January 31 (or the next business day).

Why Aren't the IRS Quarters Three Months Each?

The due dates are set in the tax code, and the IRS measures each installment against your income "to date" on a cumulative basis: the first 3 months, then 5, then 8, then the full 12. Subtract each period from the next and you get the uneven 3-2-3-4 split. That's why the June payment covers only April and May, and the January payment covers four months.

The practical effect: by the September 15 deadline, you've already earned two weeks of income that belongs to the next payment. It feels like paying Q3 "before September is over", but September was never part of it.

Does It Matter Which Months Your Income Falls In?

Less than most people think. Under the regular method, each payment is simply 25% of your required annual payment (90% of this year's tax, or 100% or 110% of last year's under the safe harbor rule). The months only matter for planning how much cash to set aside.

The months do matter if your income is uneven and you use the annualized income installment method (Form 2210, Schedule AI). That method compares each payment with the income you'd actually received by the end of each period, so a slow spring and a busy fall can mean smaller early payments without a penalty. For how to decide which period a specific payment belongs to, such as an invoice sent in March but paid in April, see which quarter income counts in.

Different Schedules: Corporations, Foundations and Fiscal Years

Who	Due Dates (Calendar Year)
Individuals and sole proprietors	April 15, June 15, September 15, January 15
C corporations	April 15, June 15, September 15, December 15 (the 15th day of the 4th, 6th, 9th and 12th months)
Private foundations and other tax-exempt organizations	May 15, June 15, September 15, December 15 (the 15th day of the 5th, 6th, 9th and 12th months)
Fiscal-year individuals	The 15th day of the 4th, 6th and 9th months of the fiscal year, and the 15th day of the 1st month after the fiscal year ends
Farmers and fishermen	One payment by January 15, or none if the return is filed and paid by March 1

A corporation's final installment falls inside its own tax year, so a calendar-year corporation's fourth payment is due December 15 rather than in January. Corporations that use the annualized method also measure income over different periods than individuals (by default the first 3, 3, 6 and 9 months), so Form 1120-W, not the individual schedule above, decides what each corporate installment covers. Private foundations pay on a slightly different schedule, with the first installment a month later (the 15th of the 5th month), and figure annualized installments on Form 990-W, which has its own periods. States set their own schedules too. Most follow the federal dates, but check your state's revenue department.

IRS Quarters vs. Calendar Quarters vs. Payroll Quarters

Three different "Q3s" are in use, which is where most of the confusion comes from:

Calendar or business Q3: July 1 – September 30. This is what "Q3 2026" means in business reports, earnings releases and shipping estimates.
Estimated tax Q3 for individuals: June 1 – August 31, paid by September 15.
Payroll Q3 (Form 941): July 1 – September 30, with the return due October 31. Employers use true calendar quarters for payroll tax returns.

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Frequently Asked Questions

What months does the September 15 estimated tax payment cover?

June 1 through August 31. The September 15 payment is the third estimated tax installment for individuals, and its period ends on August 31. Income you receive in September belongs to the fourth installment, due January 15 of the next year.

Why do I pay Q3 taxes before September is over?

Because September isn't part of the third period. For individuals, the IRS third period runs June 1 to August 31. The tax code measures installments cumulatively at 3, 5, 8 and 12 months, so the periods are 3, 2, 3 and 4 months long instead of matching calendar quarters.

What does "Q3 2026" mean?

In business and calendar terms, Q3 2026 is July 1 to September 30, 2026. For individual estimated taxes, the third 2026 period is June 1 to August 31, 2026, with the payment due September 15, 2026. Payroll returns (Form 941) use the calendar quarter.

Which months does the June 15 payment cover?

April 1 through May 31, just two months. It's the shortest estimated tax period, which is why the June payment often feels like it comes right after the April one.

What period does a corporation's or foundation's third-quarter payment cover?

A calendar-year C corporation or private foundation pays its third installment on September 15 and its fourth on December 15, within the same tax year. A foundation's first installment is due May 15, not April 15. Under the regular method each installment is 25% of the required annual payment. With the annualized method, corporations use Form 1120-W's default periods (the first 3, 3, 6 and 9 months), and foundations use Form 990-W's.

Do I have to pay the same amount every quarter?

Under the regular method, yes: each payment is 25% of your required annual payment, no matter when you earned the income. If your income is uneven, the annualized income installment method on Form 2210 lets smaller early payments count as on time when the income actually came in later. Numeris Ledger tracks income by period, so you can see which method fits.

What if a due date falls on a weekend or holiday?

The payment is on time if you make it by the next business day. For example, when September 15 falls on a Saturday, a payment made Monday, September 17 is on time. When January 15 falls on a Saturday, the following Monday is always Martin Luther King Jr. Day, so the deadline moves to Tuesday.

Tax information in this post is for general educational purposes only and does not constitute tax or legal advice. Rules and due dates can change; consult our CPA for guidance specific to your situation.

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