Revenue and expense accounts are closed at the end of each reporting period by resetting their balances to zero. This allows the firm to 1) determine its net profit for the period, 2) reset balances so net profit can be calculated for the next period, and 3) complete the accounting cycle and prepare required financial reports. Closing is necessary to comply with accounting principles such as the reporting period principle and relevance, which require separating transactions and financial results into discrete accounting periods.