Accounting

Double-Entry Bookkeeping

Every transaction gets recorded in two matched parts, so the books stay in balance with the accounting equation automatically — and errors become visible instead of invisible.

Definition

Double-entry bookkeeping is the method accountants use to record every transaction in two matched parts, of equal dollar value: one entry called a debit and one called a credit. Every transaction affects at least two accounts this way, and the total of all debit entries always equals the total of all credit entries.

Debit and credit don't mean "subtract" and "add" the way they do in everyday language — they just mean the left side and the right side of an entry. Whether a debit increases or decreases a given account depends on what kind of account it is: a debit increases assets and expenses, but decreases liabilities, equity, and revenue; a credit does the reverse.

Why this exists

The accounting equation has to hold after every single transaction a business makes, not just when someone checks the books at year-end. If you only recorded one side of a transaction — say, tracking cash leaving a bank account without recording what it was spent on — there'd be no way to tell, just from the records, whether the books still reflect reality. An error or omission could sit unnoticed indefinitely, because nothing in a single-sided record forces anyone to check it against anything else.

Double-entry bookkeeping fixes this by requiring every transaction to be recorded in two matched parts of equal value, spread across at least two different accounts. Because each transaction is built to keep total debits equal to total credits, the accounting equation stays true after every entry, automatically. If total debits and total credits in the books ever stop matching, that mismatch is itself the signal that something was recorded incorrectly — the system catches its own errors, rather than relying on someone noticing that something looks off.

This is also why debits and credits behave the way they do. Assets sit on one side of the accounting equation, and liabilities plus equity sit on the other, so a debit (which increases assets) has to be offset by a credit (which increases liabilities or equity) to keep the equation balanced — the two sides of every entry exist specifically to preserve that identity.

Formula & mechanics

Which side of an entry increases a given account depends on the account type:

Assets & Expenses:            increase with a debit,  decrease with a credit
Liabilities, Equity & Revenue: increase with a credit, decrease with a debit

Every recorded transaction lists its debits and credits side by side, and the two columns always have to total the same amount — that running check is what keeps the books balanced.

Worked example

Back to Maria's bakery: she takes out a $5,000 loan, then later spends $2,000 cash on flour and sugar (inventory).

Taking out the $5,000 loan:
  Debit  Cash (asset)              $5,000
  Credit Loan Payable (liability)  $5,000

Buying $2,000 of flour and sugar with cash:
  Debit  Inventory (asset)         $2,000
  Credit Cash (asset)              $2,000

In the first entry, an asset (cash) and a liability (the loan) both increase together — a debit on one side, a credit on the other, of equal size. In the second entry, both accounts are assets: cash decreases (a credit) exactly as inventory increases (a debit), so total assets don't change at all. Either way, total debits equal total credits, and the accounting equation stays true.

Common misconceptions

“A debit always means money is being taken out, like a bank debit card.”
In accounting, a debit just means the left side of an entry — whether it increases or decreases a balance depends on the account type. A debit card happens to decrease your balance because, from the bank's point of view, your account is a liability (money the bank owes you), and decreasing a liability is recorded as a debit — the everyday meaning and the accounting meaning point in different directions.
“Double-entry bookkeeping means every transaction gets recorded twice, doubling the work.”
Each transaction is recorded once, but that one entry has two sides — a debit and a credit — that must balance. It's not duplicate recording of the same transaction; it's recording where the value came from and where it went in a single entry.
“If total debits equal total credits, the books must be completely correct.”
Balancing only catches certain kinds of errors. Recording a transaction with the correct debit-and-credit split but in the wrong accounts entirely would still leave total debits equal to total credits — the system catches internal inconsistency, not every possible mistake.

Also in the Glossary: Credit (Accounting), Debit, Double-Entry Bookkeeping