double-entry bookkeeping

Double-entry bookkeeping is an accounting method in which every financial transaction is recorded as equal debits and credits in at least two accounts. The method produces a self-balancing system: because every debit has a corresponding credit, the total of all debit balances must equal the total of all credit balances at any point in time. This equality — verified through the trial balance — makes arithmetic errors detectable and provides a structural check against incomplete recording.

The system was first codified by Luca Pacioli in Summa de Arithmetica, Geometria, Proportioni et Proportionalita (1494), though Venetian merchants had used it for at least a century before publication [citation needed]. Pacioli didn’t invent the method; he documented existing practice and gave it systematic form.

Double-entry bookkeeping rests on the accounting equation:

Every transaction maintains this equation. Buying equipment with cash, for example, increases one asset (equipment) and decreases another (cash) — the equation stays balanced. Borrowing money increases an asset (cash) and increases a liability (the loan) — the equation stays balanced. The system can’t record a one-sided event; if only one account has been affected, the entry is incomplete.