The expense recognition principle states that expenses should be recognized in the same period as the revenues to which they relate. If this were not the case, expenses would likely be recognized as incurred, which might predate or follow the period in which the related amount of revenue is recognized.
For example, a business pays $100,000 for merchandise, which it sells in the following month for $150,000. Under the expense recognition principle, the $100,000 cost should not be recognized until the following month, when the related revenue is also recognized. Otherwise, expenses will be overstated by $100,000 in the current month, and understated by $100,000 in the following month.
This also has an impact on income taxes. In the example, income taxes will be underpaid in the current month, since expenses are too high, and overpaid in the following month, when expenses are too low.
Some expenses are difficult to correlate with revenue, such as administrative salaries, rent, and utilities. These expenses are designated as period costs, and are charged to expense in the period with which they are associated. This usually means that they are charged to expense as incurred.
The expense recognition principle is a core element of the accrual basis of accounting, which holds that revenues are recognized when earned and expenses when consumed. If a business were to instead recognize expenses when it pays suppliers, this is known as the cash basis of accounting.
If a company wants to have its financial statements audited, it must use the expense recognition principle when recording business transactions. Otherwise, the auditors will refuse to render an opinion on the financial statements.