The U.S. tax year runs from January 1 to December 31

For most people and businesses, the tax year is the calendar year: January 1 through December 31. This is the period the IRS uses to measure your income, deductions, and tax liability. Your 2024 tax return, filed in early 2025, covers income you earned from January 1, 2024, through December 31, 2024.

The calendar year is the default. You do not have to request it or do anything special to use it. When you file your tax return, you are reporting what happened during that specific calendar year.

Key Takeaways

  • The standard tax year for individuals and most small businesses is January 1 through December 31 each year.
  • Some business structures, including partnerships and S corporations, can request a different tax year from the IRS if they meet specific requirements.
  • Your tax return is always due by April 15 of the year following the tax year you are reporting — so your 2024 return is due April 15, 2025.
  • The IRS important date applies to federal taxes; your state may have a different due date, though most align with the federal date.
  • If you miss the April 15 important date, you can request an extension to October 15, but taxes owed are still due on April 15.

Who must use the calendar tax year

If you are a sole proprietor, a partner in a partnership, or an S corporation shareholder, you generally must use the calendar year. The IRS requires these business structures to align with the calendar unless you can show a business purpose for a different year.

Corporations (C corporations) have more flexibility. They can choose a fiscal year — any 12-month period — as long as they are consistent and notify the IRS. A fiscal year might run from July 1 to June 30, or October 1 to September 30, depending on when the business's natural operating cycle ends.

Individuals always use the calendar year. You cannot choose a different tax year, even if your business operates on a different schedule.

What a fiscal year is and when it applies

A fiscal year is any 12-month period used for accounting and tax purposes. It does not have to match the calendar. A retail business might choose a fiscal year ending January 31, after the holiday season closes out. A school district might use July 1 to June 30, matching the academic calendar.

If your business uses a fiscal year, your tax return is still due on the 15th day of the fourth month after your fiscal year ends. So if your fiscal year ends June 30, your return is due October 15. You report income earned during that specific 12-month period, not the calendar year.

Changing your tax year requires IRS approval. You file Form 1128, process for Change in Accounting Period, and must show a substantial business reason — not just convenience. The IRS grants some requests and denies others.

When your return is due and what happens if you miss the important date

Your federal tax return is due by April 15 of the year following the tax year you are reporting. For the 2024 tax year, the important date is April 15, 2025. This applies whether you owe taxes or expect a refund.

If you cannot file by April 15, you can request an automatic extension using Form 4868 (for individuals) or Form 7004 (for businesses). The extension gives you until October 15 to file your return. However, the extension is for filing only — if you owe taxes, they are still due on April 15. Paying late triggers interest and penalties.

If you file after April 15 without an extension, the IRS charges a failure-to-file penalty on top of any taxes owed. The penalty is usually 5 percent of unpaid taxes for each month the return is late, up to 25 percent.

State tax year important date and differences

Most states align their tax year with the federal calendar year and use the same April 15 important date. However, some states have different rules. A few states do not have an income tax at all. Others allow businesses to use a fiscal year if the federal return uses one.

Check your state's tax authority website for the exact important date and any differences from federal rules. If your state important date is earlier than April 15, that earlier date is when you must file to avoid state penalties, even if the federal important date is later.

How the tax year affects quarterly estimated taxes

If you are self-employed or have income not subject to withholding, you may owe quarterly estimated taxes. These are due on specific dates throughout the tax year, not all at once on April 15.

For the calendar tax year, estimated tax payments are due April 15, June 15, September 15, and January 15 of the following year. If you use a fiscal year, the due dates shift to match your year-end. The IRS publishes the exact dates each year on its website.

Missing a quarterly payment triggers penalties and interest, even if you ultimately owe no tax or receive a refund. Paying on time, even if the amount is small, avoids these charges.

How the tax year affects record-keeping

Your tax year determines which documents you need to keep and for how long. You must retain records — receipts, invoices, bank statements, mileage logs — for the full 12-month period you are reporting, plus three years after you file.

If you change your tax year, you will have a short year (fewer than 12 months) during the transition. You report income only for that shorter period and file a return for it. Keep records for that short year separately from the years before and after.

The IRS can audit returns for up to three years after filing, or longer if it suspects underreporting. Organized records by tax year make an audit easier to handle.

Frequently Asked Questions

Can I choose a different tax year than January 1 to December 31?

If you are an individual, no. You must use the calendar year. If you own a C corporation, you can choose a fiscal year by filing Form 1128 with the IRS. Partnerships and S corporations can request a different year only if they meet specific IRS requirements and show a business purpose.

What if my business operates on a different schedule than the calendar year?

You still report your income for the tax year you use — calendar or fiscal. Your business operations do not have to match your tax year. Many businesses operate year-round but report income on a fiscal year that matches their peak season or accounting cycle.

Do I have to file by April 15 if I expect a refund?

You are not required to file by April 15 if you do not owe taxes, but filing earlier means you receive your refund sooner. The IRS processes refunds faster for returns filed early in the season. If you are owed a refund, there is no penalty for filing late, but you will not receive the money until you file.

What happens if April 15 falls on a weekend or holiday?

The IRS moves the important date to the next business day. If April 15 is a Saturday, the important date becomes Monday, April 17. If it falls on a Sunday, the important date is Monday, April 16. The IRS announces the exact important date each year on its website.

Does my state have a different tax year than the federal government?

Most states use the same calendar year and April 15 important date as the federal government. A few states have different important date or allow fiscal years for certain business types. Check your state's tax authority website for the specific rules that explore to you.