Business quarters are the four three-month segments that make up a company’s financial year. For most individuals and small businesses, the quarters follow the calendar: Q1 runs January through March, Q2 April through June, Q3 July through September, and Q4 October through December. Companies that use a fiscal year instead start their Q1 in a different month, but the structure is the same. Those four blocks set the pace for estimated income taxes, payroll filings, and public-company earnings reports.
Calendar Quarter Dates
If you file on the standard calendar year (January 1 through December 31), your quarters are:
- Q1: January 1 through March 31
- Q2: April 1 through June 30
- Q3: July 1 through September 30
- Q4: October 1 through December 31
Calendar-year reporting is the default for individual tax returns on Form 1040, and the IRS requires it if you don’t keep formal books or haven’t adopted a fiscal year.
Fiscal Quarters and Why They Differ
A fiscal year can begin in any month. Quarters follow in three-month blocks from that starting point, so a company that opens its books on July 1 has a Q1 ending September 30. The U.S. federal government starts its fiscal year on October 1, making its Q1 October through December and its Q4 the July through September stretch.
Businesses adopt non-calendar years for practical reasons. A retailer built around the holiday season might close its books on January 31 so the full holiday cycle and post-holiday returns land in a single reporting year. That produces cleaner annual comparisons. An off-calendar year-end can also lower audit costs, because the work falls outside the January-through-April window when calendar-year filers are competing for the same auditors.
The IRS lets a business adopt a fiscal year as long as it keeps books and records on that cycle. Without consistent books, the calendar year applies by default.
The 52-53 Week Year
Some retailers and manufacturers use a 52-53 week fiscal year, which always ends on the same day of the week, such as the last Saturday in January. The year contains 52 weeks most of the time and 53 occasionally, but every quarter covers a consistent number of business days. That makes week-over-week and quarter-over-quarter sales comparisons more meaningful than one where some months have four weekends and others have five. For tax deadline purposes, the IRS treats a 52-53 week year as beginning on the first day of the nearest calendar month and ending on the last day of the nearest calendar month.
Quarterly Estimated Tax Deadlines
If you’re self-employed, a freelancer, or earning income that isn’t subject to withholding, the IRS wants your income tax in four installments across the year rather than a single April payment. Individuals who expect to owe $1,000 or more after withholding and credits must send estimated payments using Form 1040-ES. Corporations owe estimated tax once they expect to owe $500 or more.
The 2026 deadlines for calendar-year taxpayers are:
- Q1 payment: April 15, 2026
- Q2 payment: June 15, 2026
- Q3 payment: September 15, 2026
- Q4 payment: January 15, 2027
The spacing isn’t even. Q1 and Q2 sit only two months apart, and the gap widens between Q2 and Q3. When a due date falls on a weekend or a legal holiday in the District of Columbia, the deadline moves to the next business day.
Avoiding the Underpayment Penalty
Missing or underpaying an installment triggers a penalty that works like interest on the shortfall, compounding daily from the date the payment was due. For the first half of 2026, the IRS is charging 7% on underpayments in Q1 and 6% in Q2, calculated as the federal short-term rate plus three percentage points, and the same rates apply to individuals and corporations.
You avoid the penalty outright if your total tax due at filing is under $1,000. Beyond that, two safe harbors apply. You’re protected if you paid at least 90% of the current year’s tax, or at least 100% of the prior year’s tax, whichever is smaller. Higher earners face a tougher version: if your adjusted gross income exceeded $150,000 in the prior year ($75,000 if married filing separately), the prior-year threshold rises to 110%.
If your income arrives unevenly, such as a big capital gain in Q4 or a seasonal business that earns most of its revenue in summer, the annualized income installment method lets you base each quarterly payment on the income you actually earned during that period. You’ll file Schedule AI with Form 2210 at tax time. The math is heavy, but it can spare you penalties on income you hadn’t earned yet when the earlier payment was due.
Quarterly Payroll Filings
Employers have a separate quarterly obligation. Form 941, the Employer’s Quarterly Federal Tax Return, reports federal income tax withheld from wages plus both the employer and employee shares of Social Security and Medicare tax. It applies whether you have one employee or a thousand.
Form 941 is due the last day of the month after each quarter closes:
- Q1 (January through March): due April 30
- Q2 (April through June): due July 31
- Q3 (July through September): due October 31
- Q4 (October through December): due January 31
If you deposited every tax on time during the quarter, you get an extra 10 calendar days to file. Miss the deadline and the failure-to-file penalty is 5% of the unpaid tax for each month the return is late, capped at 25%.
Very small employers with $1,000 or less in annual employment tax liability may qualify to file Form 944 once a year instead of Form 941 quarterly, but only when the IRS has notified them to do so. Seasonal employers can skip quarters in which no wages were paid, provided they’ve checked the seasonal employer box on their most recent return.
Public Company Quarterly Reports
Publicly traded companies have a legal obligation to report results every quarter. SEC Rule 13a-13 requires companies registered under the Securities Exchange Act to file Form 10-Q for each of the first three quarters of the fiscal year. The fourth quarter is absorbed into the annual report on Form 10-K. Large accelerated and accelerated filers must file the 10-Q within 40 days of quarter-end; smaller companies get 45 days. Most public companies pair the filing with an earnings call where management walks analysts through the numbers and often offers guidance for the rest of the year.
When a Quarter Doesn’t Line Up
Not every business gets four full quarters in a year. A company incorporated in August that adopts the calendar year files a first return covering only August through December. A business that dissolves mid-year files a final return through its last day of existence. These partial-year returns are called short tax years, and they also appear when a business changes its fiscal year and needs a bridge return covering the gap. In most cases, a short-period return is due when it would be if the short period were a full 12-month year ending on the same date.
One narrow exception: if you’re switching to or from a 52-53 week fiscal year and the resulting short period is six days or fewer, the IRS doesn’t treat it as a separate tax year. Those days roll into the following year’s return.