An accounting period is the recurring window of time a business uses to measure its financial results and report income to the IRS. Most businesses use a 12-month period, either a calendar year or a fiscal year, and the one you use determines when your tax return is due, what forms apply, and — for partnerships and S corporations — how much choice you have at all. The rest of this guide walks through the two main types, which entities are locked into which, and what it takes to change once you’ve picked one.
Calendar Year vs. Fiscal Year
Federal tax law recognizes two flavors of 12-month accounting period. A calendar year runs January 1 through December 31. A fiscal year is any other 12-month period that ends on the last day of a month other than December.1Office of the Law Revision Counsel. 26 USC 441 Period for Computation of Taxable Income
The calendar year is the more common choice, especially for individuals and sole proprietors, because it lines up with the personal tax return cycle. If you keep no books or have no established annual accounting period, the IRS defaults you to a calendar year automatically.1Office of the Law Revision Counsel. 26 USC 441 Period for Computation of Taxable Income
A fiscal year makes sense when the business has a natural cycle that doesn’t align with the calendar. A retailer might end its year on January 31 to keep the full holiday season and post-holiday returns in one reporting period. A summer tourism company might pick September 30 so peak season doesn’t get split across two years. Matching your period to your revenue cycle produces cleaner statements and more meaningful year-over-year comparisons.
Which Accounting Period Your Business Can Use
Not every business gets to pick freely. C corporations have the most flexibility. Pass-through entities face strict rules meant to stop owners from deferring income by putting the entity on a different tax year than the people who report its income.
C Corporations
A C corporation can adopt either a calendar year or any fiscal year when it files its first return. This is the one entity type where the choice is genuinely open. The corporation begins keeping books on its chosen cycle and files accordingly.
Sole Proprietorships
A sole proprietorship isn’t a separate tax entity. It reports on the owner’s individual return, so it uses the same tax year as the owner. Since most individuals use a calendar year, the sole proprietorship does too. The only way around this is keeping adequate books on a different fiscal year cycle, which is rare in practice.2Internal Revenue Service. Tax Years
Partnerships
A partnership must use the tax year of partners who own more than 50% of profits and capital, known as the majority interest taxable year. If no single year meets that threshold, the partnership must use the tax year of all principal partners (those owning 5% or more). If even that produces no common year, the default is a calendar year. A partnership can use a different year only by establishing a legitimate business purpose to the IRS’s satisfaction, and deferring income to partners does not count as a business purpose.3Office of the Law Revision Counsel. 26 USC 706 Taxable Years of Partner and Partnership
S Corporations and Personal Service Corporations
An S corporation must use a permitted year, which generally means a calendar year. The only alternatives are a year elected under Section 444, a 52-53 week year that references the calendar year, or a fiscal year for which the corporation proves a business purpose.4eCFR. 26 CFR 1.1378-1 Taxable Year of S Corporation Personal service corporations face the same restriction. If the owner-employees are mostly on a calendar year, the IRS wants the entity on a calendar year too.1Office of the Law Revision Counsel. 26 USC 441 Period for Computation of Taxable Income
The Section 444 Election
If your partnership, S corporation, or personal service corporation is stuck with a required calendar year but a fiscal year would suit the business better, Section 444 offers a workaround. The election lets you adopt a tax year other than the required one, with a ceiling on how much deferral you can create.5Justia Law. 26 USC 444 Election of Taxable Year Other Than Required Taxable Year
The trade-off is real. Partnerships and S corporations that elect under Section 444 must make annual required payments to the IRS on Form 8752 that approximate the tax deferral the owners would otherwise enjoy. Personal service corporations face a different constraint: if the corporation doesn’t distribute enough compensation to employee-owners during the deferral period, its deduction for those payments gets capped.6Office of the Law Revision Counsel. 26 USC 280H Limitation on Certain Amounts Paid to Employee-Owners by Personal Service Corporations Electing Alternative Taxable Years These rules exist to neutralize the deferral advantage, so the Section 444 election is mainly useful for operational or reporting reasons rather than tax savings.
The 52-53 Week Tax Year
Some businesses run on weekly cycles where a fixed calendar date matters less than always ending on the same day of the week. A grocery chain or a payroll-driven operation might prefer ending every fiscal year on the last Saturday in January. The 52-53 week election allows exactly that. The year always ends on the same weekday, either the last time that day falls in a given month or the occurrence nearest to month-end.1Office of the Law Revision Counsel. 26 USC 441 Period for Computation of Taxable Income
The year alternates between 52 and 53 weeks, which keeps each period close to 12 months without ever landing on a mid-week date. One wrinkle: if switching to or from a 52-53 week year produces a short period of fewer than 7 days, the IRS treats those days as part of the following tax year rather than requiring a separate short-year return.1Office of the Law Revision Counsel. 26 USC 441 Period for Computation of Taxable Income
Changing Your Accounting Period
Once you’ve established a tax year, switching to a different one requires IRS approval. Section 442 is blunt: a new accounting period becomes your taxable year only if the Secretary approves the change.7Office of the Law Revision Counsel. 26 USC 442 Change of Annual Accounting Period The vehicle for requesting approval is Form 1128.
Automatic Approval
Some changes qualify for automatic approval, meaning you file Form 1128 and follow the procedural rules without needing individual IRS review. Corporations other than S corporations and personal service corporations are the main candidates for this streamlined path. Even they get disqualified if they’ve changed their accounting period within the past 48 months, hold an interest in certain pass-through entities, or fall into other categories listed in the Form 1128 instructions.8Internal Revenue Service. Instructions for Form 1128
A corporation disqualified from automatic approval on technical grounds can still qualify if it’s changing to a natural business year that passes the 25% gross receipts test. That test looks at whether gross receipts from the last two months of the requested fiscal year equal or exceed 25% of total annual gross receipts, calculated across three consecutive 12-month periods.9Internal Revenue Service. Rev. Proc. 2002-38 A ski resort requesting a May 31 year-end would need to show that April and May consistently produce at least a quarter of the year’s revenue.
Non-Automatic Approval
If you don’t qualify for automatic approval, you file Form 1128 and make the case to the IRS directly. You’ll need to demonstrate a substantial business purpose. The IRS weighs whether the new year creates or reduces income deferral, whether the business has a natural cycle that favors the requested year, and whether the change is being made for administrative convenience. This path takes longer, and the outcome is less predictable.
Short Tax Years
A short tax year is any period shorter than 12 full months. Two situations trigger one: a change in accounting period with IRS approval, or a business that doesn’t exist for an entire taxable year because it started mid-year or dissolved before year-end.10Office of the Law Revision Counsel. 26 USC 443 Returns for a Period of Less Than 12 Months
When a short year results from changing your accounting period, the IRS doesn’t tax you on those few months of income at normal rates. Your taxable income gets annualized: multiply by 12, divide by the number of months in the short period, compute the tax on that annualized amount, then prorate back down. The math prevents you from bunching deductions into a short period to land in a lower bracket. If you can show what your income would have been for the full 12-month period beginning on the first day of the short period, you can ask the IRS to compute your tax based on that actual figure instead, which sometimes produces a lower bill.10Office of the Law Revision Counsel. 26 USC 443 Returns for a Period of Less Than 12 Months
Filing Deadlines Tied to Your Accounting Period
Your accounting period directly sets your return due date. Deadlines run from the end of your tax year, not from a fixed calendar date, so a fiscal-year business has a completely different filing schedule than a calendar-year one.11Internal Revenue Service. Starting or Ending a Business
- Sole proprietors file by the 15th day of the fourth month after the tax year ends. For calendar-year filers, that’s April 15.
- Partnerships file Form 1065 by the 15th day of the third month after year-end. Calendar-year partnerships file by March 15.
- S corporations file Form 1120-S by the 15th day of the third month after year-end. Calendar-year S corps also file by March 15.
- C corporations file Form 1120 by the 15th day of the fourth month after year-end. A calendar-year C corp files by April 15. One exception: a C corporation with a fiscal year ending June 30 files by the 15th day of the third month, which is September 15.
Partnerships and S corporations file earlier than C corporations because their income flows through to the owners’ individual returns. Owners need K-1 information from the entity return before they can finish their personal filings. Miss the entity deadline and you’re not just late on one return; you’re potentially delaying every partner’s or shareholder’s individual return along with it.