For individuals and most small businesses, the first quarter ends on March 31, closing out January, February, and March of the calendar year.1Internal Revenue Service. Publication 509 (2026), Tax Calendars That date is fixed; a leap year changes February’s length but not the quarter’s end. The federal government, however, runs on a different clock, and companies that use a non-calendar fiscal year end their first quarter on a different date entirely.
The Calendar-Year First Quarter Ends March 31
If you file taxes on a calendar-year basis, your first quarter runs January 1 through March 31. Unless you have adopted a different fiscal year, the IRS treats the calendar year as your default accounting period.2Internal Revenue Service. Tax Years Most individual filers, sole proprietors, and small businesses fall into this group by default.
The Federal Government’s First Quarter Ends December 31
The United States federal government does not follow the calendar year. Federal law sets the government’s fiscal year to begin October 1 and end September 30 of the following year, which puts the first federal quarter from October 1 through December 31.3Office of the Law Revision Counsel. 31 USC 1102 – Fiscal Year
This matters when you’re reading news about federal spending, contracts, or budget cycles. A reference to “first-quarter federal spending” means October through December, not January through March.
Corporations Can Set Their Own First Quarter
The IRS allows corporations and other entities to adopt a fiscal year that ends on the last day of any month other than December, or to use a 52–53-week tax year.2Internal Revenue Service. Tax Years A retailer might start its year in February so holiday returns fall neatly at the close of the prior year; a resort might begin in April to match its travel season. The first quarter shifts with the fiscal year, so a company you’re tracking may close Q1 in April, May, or any other month.
A business adopts its tax year by filing its first income tax return using that period. If you keep no books, have no regular accounting period, or your chosen year doesn’t qualify as a fiscal year, the IRS requires the calendar year.
Individual Deadlines After March 31
March 31 itself isn’t a filing date, but April 15 is one of the busiest days on the tax calendar for calendar-year filers.
Annual Return
Your federal income tax return for the prior year is due April 15. For 2026, that means the 2025 return must be filed, or an extension requested, by Wednesday, April 15, 2026.4Internal Revenue Service. IRS Announces First Day of 2026 Filing Season An extension buys more time to file, not more time to pay.
First Estimated Tax Payment
If you’re self-employed, a freelancer, a retiree, or an investor without enough tax withheld from your income, you owe quarterly estimated payments. The first payment, covering income earned January 1 through March 31, is due April 15. The other three are due June 15, September 15, and January 15 of the following year. Missing a payment or paying too little can trigger a penalty that accrues even if you’re ultimately owed a refund when you file.5Internal Revenue Service. When Are Quarterly Estimated Tax Payments Due?
Prior-Year IRA and HSA Contributions
April 15 is also the last day to make IRA and HSA contributions that count toward the prior tax year. You can deposit money into a Traditional or Roth IRA for the 2025 tax year up until April 15, 2026.6Internal Revenue Service. Retirement Topics – IRA Contribution Limits The same April 15 deadline applies to Health Savings Account contributions for the prior year.7Internal Revenue Service. Instructions for Form 8889
Employer Deadlines After March 31
Businesses with employees have their own set of first-quarter obligations that fall right after the quarter closes.
Form 941
Employers who withhold federal income tax, Social Security, and Medicare from employee wages file Form 941 each quarter. The first-quarter return is due April 30. If you deposited all taxes for the quarter on time and in full, you get an extra ten days, moving the deadline to May 10.8IRS.gov. Instructions for Form 941
FUTA Deposits
If your federal unemployment tax liability exceeds $500 for the quarter, you must deposit it by the end of the following month, meaning April 30 for Q1.9Internal Revenue Service. Topic No. 759, Form 940 – FUTA Tax Return Filing and Deposit Requirements If your liability is $500 or less, it carries forward to the next quarter until the cumulative total crosses the threshold.
State Sales Tax
Businesses that collect sales tax and file quarterly typically owe their first-quarter return sometime between mid-April and the end of April. Exact deadlines vary by state and can shift when they fall on a weekend or holiday. Check with your state’s department of revenue.
SEC 10-Q Filings
Publicly traded companies file Form 10-Q with the Securities and Exchange Commission after each of the first three quarters. No 10-Q is required for the fourth quarter because the annual Form 10-K covers it. The filing window depends on company size: 40 days after quarter-end for large accelerated and accelerated filers, and 45 days for all other registrants.10Securities and Exchange Commission. Form 10-Q General Instructions
For a company on the calendar year, that puts the first-quarter 10-Q around May 10 for a large accelerated filer and roughly May 15 for a smaller registrant.