Double-entry bookkeeping

Double-entry bookkeeping, also known as double-entry accounting, is a method of bookkeeping in which every financial transaction is recorded with equal and opposite entries in at least two accounts, ensuring that total debits equal total credits. The double-entry system records two sides, known as debit and credit, following the principle that for every debit there must be an equal and opposite credit. A transaction in double-entry bookkeeping always affects at least two accounts, always includes at least one debit and one credit, and always has total debits and total credits that are equal. The purpose of double-entry bookkeeping is to maintain accuracy in financial records and allow detection of errors or fraud.

For example, if a business takes out a bank loan for $10,000, recording the transaction in the bank's books would require a debit of $10,000 to an asset account called "Loan Receivable", as well as a credit of $10,000 to an asset account called "Cash". For the borrowing business, the entries would be a $10,000 debit to "Cash" and a credit of $10,000 in a liability account "Loan Payable". For both entities, total equity, defined as assets minus liabilities, has not changed.

The basic entry to record this transaction in the example bank's general ledger will look like this:

Double-entry bookkeeping is based on "balancing" the books; that is to say, satisfying the accounting equation. The accounting equation serves as an error detection tool: if at any point the sum of debits for all accounts does not equal the corresponding sum of credits for all accounts, an error has occurred. However, satisfying the equation does not necessarily guarantee a lack of errors. For example, the wrong accounts could have been debited or credited.

The earliest extant accounting records that follow the modern double-entry system in Europe come from Amatino Manucci, a Florentine merchant at the end of the 13th century. Manucci was employed by the Farolfi firm and the firm's ledger of 1299–1300 evidences full double-entry bookkeeping. Giovannino Farolfi & Company, a firm of Florentine merchants headquartered in Nîmes, acted as moneylenders to the Archbishop of Arles, their most important customer. Some sources suggest that Giovanni di Bicci de' Medici introduced this method for the Medici bank in the 14th century, though evidence for this is lacking.

The double-entry system began to propagate between Italian merchant cities during the 14th century. Before this, there may have been systems of accounting records on multiple books which did not yet have the formal and methodical rigor necessary to control the business economy. In the course of the 16th century, Venice produced the theoretical accounting science by the writings of Luca Pacioli, Domenico Manzoni, Bartolomeo Fontana, the accountant Alvise Casanova and the erudite Giovanni Antonio Tagliente.

Benedetto Cotrugli (Benedikt Kotruljević), a Ragusan merchant and ambassador to Naples, described double-entry bookkeeping in his treatise Della mercatura e del mercante perfetto. Although it was originally written in 1458, no manuscript older than 1475 is known to remain, and the treatise was not printed until 1573. The printer shortened and altered Cotrugli's treatment of double-entry bookkeeping, obscuring the history of the subject. Luca Pacioli, a Franciscan friar and collaborator of Leonardo da Vinci, first codified the system in his mathematics textbook Summa de arithmetica, geometria, proportioni et proportionalità published in Venice in 1494. Pacioli is often called the "father of accounting" because he was the first to publish a detailed description of the double-entry system, thus enabling others to study and use it.

In early modern Europe, double-entry bookkeeping had theological and cosmological connotations, recalling "both the scales of justice and the symmetry of God's world".