Time Period Assumption

The time period assumption, also called the periodicity assumption, holds that the economic life of a business can be divided into shorter, equal time periods for reporting purposes. Although a company operates continuously, investors, lenders, managers and tax authorities need regular information about its performance, so accountants prepare financial statements for set intervals, typically a month, a quarter and a year.

It is one of the basic assumptions underlying financial accounting, alongside the economic entity assumption, the monetary unit assumption and the going concern assumption. Together these assumptions support the accounting principles used to prepare financial statements under US GAAP and IFRS.

• Annual period: the main reporting period is the fiscal year. Many companies use the calendar year, but others choose a year ending at a seasonal low point, such as 31 January for many US retailers after the holiday season, or a 52- or 53-week year ending on the same weekday.
• Quarterly reporting: US public companies file quarterly reports on Form 10-Q with the Securities and Exchange Commission for the first three quarters and an annual report on Form 10-K.
• Monthly management accounts: most businesses close their books monthly for internal reporting.
• Interim financial statements: any statements covering less than a full year, which follow specific rules on how annual costs and taxes are spread.

Dividing a continuous business into periods creates a problem: many transactions span more than one period. Insurance is paid for a year in advance, equipment lasts for a decade, employees earn wages for days not yet paid, and customers pay deposits for work to be done next quarter. The time period assumption is the reason accountants need the accrual basis of accounting, the revenue recognition rules and the matching principle: they determine which period each revenue and expense belongs to.

At the end of each period, adjusting entries assign amounts to the correct period, and closing entries reset revenue and expense accounts for the next one.

On 1 October, a company with a 31 December year end pays $12,000 for a one-year insurance policy. Under the time period assumption, the cost must be spread across the periods that benefit:

Here $\text{Total cost}$ is $12,000, the months in the current year covered are 3 and the total months covered are 12. Insurance expense for the year is $3,000, and the remaining $9,000 is reported as prepaid insurance, to be expensed over the next nine months. If the company prepares quarterly statements, the fourth quarter bears $3,000 and each of the first three quarters of the next year bears $3,000.

Shorter periods make information more timely, but they rely more on estimates, because fewer transactions are complete when the books are closed. Quarterly profits can swing because of seasonal patterns or the timing of large contracts, and some critics argue that a focus on quarterly results encourages short-term thinking by managers. Period-end cut-off is also a common area for errors and manipulation, such as recording sales just before the period ends that really belong to the next. Auditors therefore test transactions around the balance sheet date to check that they have been recorded in the correct period.