Should My Business Use a Calendar Year or a Fiscal Year for Taxes?

By Bill Stilwell · Last reviewed October 17, 2026

The short answer

Your tax year is the 12-month period you use to report income and expenses to the Internal Revenue Service (IRS). Most small businesses use the calendar year, January through December. A fiscal year ends on the last day of any other month. You adopt your tax year by filing your first return with it, and changing it later generally needs IRS approval on Form 1128.

What this means

The IRS recognizes three kinds of tax years:

Calendar year: 12 months ending December 31.
Fiscal year: 12 months in a row ending on the last day of any month except December.
52 to 53 week year: a fiscal year that always ends on the same day of the week, so it may not end on the last day of a month.

The IRS says anyone can use the calendar year. You must use it if you keep no books or records, have no annual accounting period, or your year doesn’t qualify as a fiscal year.

You adopt a tax year by filing your first income tax return using it. The IRS says applying for an Employer Identification Number (EIN), asking for an extension, or paying estimated taxes doesn’t adopt a tax year.

For a sole proprietor or single-member LLC owned by one person, the business usually reports on the owner’s personal return, so it follows the owner’s tax year, which is almost always the calendar year. IRS Publication 538 explains extra rules for partnerships, S corporations, and personal service corporations, which often must use a year tied to their owners’ years unless an exception applies.

Made-up example: Coastal Kayak Rentals does most of its business in summer. The owner asks her CPA about a fiscal year ending in October so year-end closing falls after the busy season. Her CPA checks whether her entity type allows it before she files her first return.

Why it matters

It sets every deadline. Return due dates are counted from the end of your tax year (see 10.1.6 Federal Filings).
It shapes your books. Your accounting software, reports, and state filings should all use the same year.
It’s hard to change. The IRS generally requires approval, and some changes need a user fee.
The wrong choice can backfire. Picking a fiscal year your entity isn’t allowed to use can create filing problems.

Who this applies to

Every business that files a federal income tax return. Most small businesses, especially sole proprietors and single-member LLCs, simply use the calendar year. A fiscal year mainly makes sense for seasonal businesses or corporations with a reason to close their books at another time. Your state generally expects your state return to use the same year, so check with your state tax department.

How to do it

Start with the calendar year unless you have a clear reason not to.
If you want a fiscal year, ask your CPA whether your entity type and owners allow it.
Set the year in your accounting software before you enter transactions (see 10.5.1 Chart of Accounts).
File your first return using that year. This is what adopts it.
Add the year end and return due dates to your financial calendar (see 10.9.1 Financial Calendar).
Record the tax year in your Master Business Record.
If you ever need to change it, talk to your CPA about Form 1128. The IRS says some changes get automatic approval with no user fee, and others need a ruling and a fee.

What proof to keep

Your first federal return, which shows the tax year
The tax year setting in your accounting software
Any Form 1128 and IRS approval letter
Your CPA’s note if you chose a fiscal year

Common mistakes

Choosing a fiscal year without checking the rules. Partnerships and S corporations often can’t pick freely.
Thinking the EIN application sets your year. It doesn’t. Your first return does.
Setting the software to a different year than your return.
Changing years without approval.
Forgetting the state. State returns usually follow the same year.

When to get help from a pro

CPA or enrolled agent: if you’re considering a fiscal year or a change. Questions to ask:

Is the calendar year right for my business, or would a fiscal year help?
Does my entity type limit which tax year I can use?
If I change later, will I get automatic approval?

Bill’s note

[Bill: add a short note. For example, which tax year SiteSmarty uses and why, or a seasonal client who benefited from thinking about this early.]

How I did this for SiteSmarty

[Date I did this:]
[What I actually did, step by step: which tax year SiteSmarty uses and where I set it]
[What it cost and how long it took:]
[What surprised me or what I’d do differently:]
[Screenshot or photo to add, with private info blurred: the accounting software tax year setting]
[Result so far:]

Questions people ask

What is a fiscal tax year? Twelve months in a row ending on the last day of any month except December.

How do I choose my tax year? You adopt it by filing your first return using it. Most small businesses use the calendar year.

Does getting an EIN set my tax year? No. The IRS says an EIN application, an extension request, or estimated payments don’t adopt a tax year.

Can I change my tax year later? Usually only with IRS approval on Form 1128. Some changes are automatic, and others need a ruling and a fee.

Do S corporations have to use the calendar year? Often, but there are exceptions. IRS Publication 538 explains the rules. Ask your CPA.

Audit check

Question: Does the business have a clear tax year that matches its returns, books, and calendar?
Pass looks like: Tax year recorded. First return, accounting software, and state filings all use it. Any change approved by the IRS.
Fail looks like: Owner unsure of the tax year. Software set to a different year. A fiscal year used without checking entity rules.
Evidence to collect: First federal return, software settings screenshot, Master Business Record entry, and any Form 1128 approval.

Where this fits

Do this first: 10.1.2 Federal Tax Classification

Do this next: 10.1.4 Accounting Method

Sources

IRS, "Tax years" (checked October 17, 2026)
IRS, Publication 538, "Accounting Periods and Methods" (checked October 17, 2026)
IRS, "Instructions for Form 1128" (checked October 17, 2026)

This page explains general rules and Bill's own experience. It is not legal, tax, or insurance advice. Talk to a qualified professional about your situation.