Double-entry bookkeeping

Double-entry bookkeeping records the effects of a transaction across accounts rather than treating it as a single isolated amount. A journal entry has one or more debits and one or more credits, with the total value on each side equal. A simple transaction may involve two accounts; a compound entry can involve several. Debit and credit are the names of the two sides of an entry, and their effect depends on the type of account.

The system is linked to the accounting equation: assets equal liabilities plus equity. Recording both sides of an event helps preserve this relationship as an organization acquires resources, incurs obligations, earns revenue or incurs expenses. For example, when a business borrows money and receives cash, the entry records an increase in cash and a corresponding increase in a loan liability.

Transactions are first entered in journals, generally in date order, with the accounts and amounts affected. The entries are then posted to a ledger, where activity is grouped by account. A trial balance lists the ledger accounts and their balances; comparing its debit and credit totals can reveal some calculation or posting errors. Equal totals do not by themselves prove that every transaction was recorded correctly—for example, a transaction omitted entirely would not make the totals unequal.

Ledger information is used to prepare financial statements. Among other things, a balance sheet summarizes assets, liabilities and equity at a point in time, while an income statement reports revenue and expenses over a period. These records help owners, managers, investors and lenders assess an organization's position and results, though the accounting system depends on accurate source records and appropriate rules for classifying transactions.

Bookkeeping has ancient precedents, but the double-entry method took shape in the commercial republics of Italy. Surviving records show early forms of the method in Genoa and Florence by the 14th century, followed by increasingly developed Venetian records. This history reflects the needs of merchants who had to track assets, debts, partners and transactions across growing commercial networks.

In 1494, the Franciscan mathematician Luca Pacioli published Summa de arithmetica, geometria, proportioni et proportionalità. The book included the first printed exposition of the Venetian double-entry method. Pacioli described and organized a practice already used by merchants; he is not considered its inventor. His account helped spread knowledge of bookkeeping beyond the circles where the methods had developed.

The method became a foundation of modern financial accounting because it provides a structured way to record the two-sided effects of transactions and assemble them into reports. It is used in many forms by businesses and other organizations, including through computerized accounting systems. The underlying logic is independent of whether records are kept in paper books or software.

Double entry is a bookkeeping framework, not a guarantee against fraud or error. A trial balance can identify certain imbalances, but transactions can be misclassified, recorded at the wrong amount, or omitted while the debit and credit totals still agree. Reliable reporting therefore also depends on documentation, review, accounting standards and internal controls.