Calendar quarters are the four three-month blocks that divide the January-through-December year into equal segments: Q1 runs January 1 through March 31, Q2 runs April 1 through June 30, Q3 runs July 1 through September 30, and Q4 runs October 1 through December 31. The IRS, the SEC, and businesses all use these fixed windows to set filing deadlines, estimated tax due dates, and financial reporting schedules. Which deadlines apply to you depends on what kind of income you earn and whether you employ anyone.
The Four Calendar Quarters
Each quarter contains roughly 13 weeks, and the dates never shift from year to year:
- Q1: January 1 – March 31
- Q2: April 1 – June 30
- Q3: July 1 – September 30
- Q4: October 1 – December 31
When an agency sets a deadline for “the last day of the month following the quarter’s end,” both sides know exactly which three months are in play. The same reference point drives earnings reports, economic data releases, and benefit periods.
Estimated Tax Deadlines for Individuals
If you earn income without automatic withholding, such as self-employment earnings, investment gains, rental income, or freelance payments, you may need to send the IRS estimated tax payments four times a year. The general rule is that you owe estimated tax if you expect your total tax bill to be $1,000 or more after subtracting withholding and credits.1Internal Revenue Service. Estimated Taxes
The four 2026 payment deadlines are:
- First payment (Q1 income): April 15, 2026
- Second payment (Q2 income): June 15, 2026
- Third payment (Q3 income): September 15, 2026
- Fourth payment (Q4 income): January 15, 2027
You can skip the January 15 payment if you file your full 2026 return and pay the entire balance by February 1, 2027.2IRS.gov. Form 1040-ES – Estimated Tax for Individuals
The Underpayment Safe Harbors
Missing a quarterly payment or paying too little can trigger an underpayment penalty. You can generally avoid it by meeting one of two safe harbors: pay at least 90 percent of the tax you owe for the current year, or pay at least 100 percent of what you owed for the prior year. If your prior-year adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the prior-year threshold rises to 110 percent.3Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty
Quarterly Payroll Tax Deadlines for Employers
Employers that pay wages subject to federal income tax withholding, Social Security, or Medicare must file IRS Form 941 after each calendar quarter. The return reports withheld income taxes along with both the employer’s and employee’s share of Social Security and Medicare taxes.4Internal Revenue Service. About Form 941, Employer’s Quarterly Federal Tax Return Federal unemployment tax (FUTA) is separate and reported annually on Form 940, not on Form 941.5Internal Revenue Service. About Form 940, Employer’s Annual Federal Unemployment (FUTA) Tax Return
Form 941 is due by the last day of the month following each quarter’s end:6Internal Revenue Service. Instructions for Form 941 (Rev. March 2026)
- Q1 (January–March): April 30
- Q2 (April–June): July 31
- Q3 (July–September): October 31
- Q4 (October–December): January 31
If you deposited all taxes for the quarter on time and in full, you get an extra 10 calendar days to file the return.6Internal Revenue Service. Instructions for Form 941 (Rev. March 2026)
Filing Form 941 is a separate obligation from depositing the taxes themselves. Depending on your total liability during a designated lookback period, you follow either a monthly or semi-weekly deposit schedule, and each has its own timing rules.7Internal Revenue Service. Employment Tax Due Dates Making a deposit on time doesn’t excuse a late return, and filing the return doesn’t excuse a late deposit.
Late Deposit Penalties
Penalties for depositing employment taxes late scale with how overdue the deposit is:
- 1–5 days late: 2 percent of the unpaid deposit
- 6–15 days late: 5 percent
- More than 15 days late: 10 percent
- More than 10 days after a first delinquency notice, or upon demand for immediate payment: 15 percent
The tiers don’t stack. A deposit more than 15 days late carries a 10 percent penalty total, not the sum of the lower tiers.8Internal Revenue Service. Failure to Deposit Penalty
SEC Quarterly Reporting Deadlines
Publicly traded companies file quarterly financial reports with the SEC on Form 10-Q. These reports cover the first three fiscal quarters; the fourth quarter’s data is rolled into the annual Form 10-K instead.9SEC.gov. Form 10-Q Each 10-Q contains financial statements, management’s discussion of the company’s financial condition, and disclosures about market risk.10U.S. Securities and Exchange Commission. Exchange Act Reporting and Registration
Deadlines depend on company size. Large accelerated filers and accelerated filers must submit Form 10-Q within 40 days after the quarter ends. All other filers have 45 days.9SEC.gov. Form 10-Q
When Quarters Don’t Match the Calendar
Not every organization uses the January-through-December year. A fiscal year is any 12 consecutive months ending on the last day of a month other than December, and the IRS also recognizes 52-to-53-week fiscal years that don’t necessarily end on a month’s last day.11Internal Revenue Service. Tax Years A company whose fiscal year begins October 1 labels October through December as its Q1, even though that same window is Q4 on the standard calendar. The federal government itself runs on an October-through-September fiscal year, which is why “fiscal year 2026” in congressional budget debates doesn’t map onto the calendar year.
You adopt a tax year by filing your first income tax return using it. Switching later requires IRS approval through Form 1128, though some changes qualify for automatic approval. If you keep no books, have no established annual accounting period, or are required by the tax code to use a calendar year, you must follow the standard January-to-December cycle.11Internal Revenue Service. Tax Years
Retailers often use a separate structure called the 4-5-4 calendar, which divides each quarter into three periods of four, five, and four weeks rather than three calendar months. The National Retail Federation developed it in the 1930s so that every comparable period contains the same number of Saturdays and Sundays, since weekend days drive a large share of retail sales.12National Retail Federation. 4-5-4 Calendar Major retailers’ quarterly filings align with this 4-5-4 structure rather than standard calendar-quarter dates, so a “Q2” in a retailer’s report may not span April through June.