📒 Double-Entry Bookkeeping

Definition and purpose of double-entry bookkeeping
The accounting equation as the foundation
Two approaches: traditional (British) and accounting equation (American)
The golden rules for real, personal, and nominal accounts
Books of accounts: nominal ledgers, daybooks, and the trial balance
Debits and credits, normal balances, and T accounts
A worked transaction example

📖 What Is Double-Entry Bookkeeping?

Double-entry bookkeeping (also called double-entry accounting) is a method of bookkeeping in which every financial transaction is recorded with equal and opposite entries (debits and credits), thus "balancing the books".

Purpose: to maintain accuracy in financial records and allow detection of errors or fraud.
Benefit: it is a standard process for tracking business transactions and improves the ability of the users of financial information to read, process, and understand the financial picture of a company's operations.
Scaling up: as the complexity and volume of transactions increases, companies use ledgers and accounting information systems to automate the tracking of individual transactions and to create financial statements.

⚖️ The Accounting Equation

The basis of double-entry bookkeeping is the accounting equation:

$\text{Assets} = \text{Liabilities} + \text{Equity}$

Every transaction recorded will keep this equation in balance.

Examples of transactions

A company buys a new piece of equipment: an asset increases.
A company spends cash: an asset is reduced.
A company takes on a loan: a liability increases.

Normal balance

Where an account sits within the accounting equation determines its normal balance. For example:

A debit to assets increases assets.
A credit to liabilities increases liabilities.

🧭 Approaches

The double-entry system can be applied using two main methods: the traditional approach (British approach) and the accounting equation approach (American approach). Regardless of the method, every transaction maintains two aspects, debit and credit.

Feature	Traditional (British) approach	Accounting equation (American) approach
Basis	Three categories of accounts and the golden rules	The accounting equation
Account classification	Real, personal, and nominal accounts	Assets, capital, liabilities, revenues/incomes, and expenses/losses

Traditional approach

Under the traditional (British) approach, accounts are divided into three categories:

Account type	What it relates to
Real accounts	Assets, both tangible and intangible in nature
Personal accounts	Persons or organisations with whom the business has transactions; mainly accounts of debtors and creditors
Nominal accounts	Revenue, expenses, gains, and losses

The golden rules of accounting guide the traditional approach:

Account type	Golden rule
Real accounts	Debit what comes in, credit what goes out
Personal accounts	Debit the receiver, credit the giver
Nominal accounts	Debit expenses and losses, credit incomes and gains

Primary journals and traceability

The great importance of the primary journals lies in the fact that they should make it possible to trace every single business transaction back to the original voucher without great effort at any given time during the retention periods, even for past events.
Thus, bank statements can be used as primary journals.
To simplify or enable the tracking of business transactions in the general ledger, it is necessary to note the account assignment on the original document or to ensure corresponding digital traceability.

Accounting equation approach

Also known as the American approach, this method records transactions on the basis of the accounting equation:

$\text{Assets} = \text{Liabilities} + \text{Equity}$

The accounting equation is a statement of equality between the debits and the credits.
The rules of debit and credit depend on the nature of an account.
All accounts are classified into five types: assets, capital, liabilities, revenues/incomes, or expenses/losses.
If there is an increase or decrease in a set of accounts, there will be an equal decrease or increase in another set of accounts.

📚 Books of Accounts

In double-entry bookkeeping, every financial transaction is entered into at least two nominal ledger accounts to ensure that total debits equal total credits, maintaining balance in the general ledger. This is a partial check that each and every transaction has been correctly recorded.

Debit and credit entries in the ledger

Each transaction is recorded as a debit entry (Dr) in one account, and a credit entry (Cr) in a second account.
Per convention, debits are posted on the left-hand side of a ledger account, while credits are posted on the right-hand side.
If the total of the entries on the debit side of one account is greater than the total on the credit side of the same nominal account, that account is said to have a debit balance.

Daybooks (journals) and the nominal ledger

Double entry is applied within nominal ledgers.
Daybooks (journals) typically serve as preliminary records and are not part of the nominal ledger itself.
The information from the daybooks is used in the nominal ledger, and it is the nominal ledgers that ensure the integrity of the resulting financial information created from the daybooks (provided that the information recorded in the daybooks is correct).
Why the separation? To limit the number of entries in the nominal ledger: entries in the daybooks can be totalled before they are entered in the nominal ledger.
If there are only a relatively small number of transactions, it may be simpler to treat the daybooks as an integral part of the nominal ledger and thus of the double-entry system.
Even so, it is still necessary to check, within each daybook, that the postings from the daybook balance.

The trial balance

Nominal ledger accounts form the basis for preparing a trial balance, which lists debit and credit balances in two columns to confirm that total debits equal total credits.

The trial balance lists all the nominal ledger account balances.
The list is split into two columns: debit balances in the left-hand column and credit balances in the right-hand column.
Another column contains the name of the nominal ledger account describing what each value is for.
The total of the debit column must equal the total of the credit column.

💳 Debits and Credits

A debit entry in an account represents a transfer of value to that account, and a credit entry represents a transfer from the account.

Since both sides of a double-entry bookkeeping entry must remain in balance, accounts have a normal balance, which is based upon whether a debit or a credit increases the account.
Due to the format of a ledger, historically debits are recorded on the left side of the ledger, and credits are recorded on the right side.
This may be represented graphically with the use of a T account.

Side of the ledger	Entry type
Left	Debit (Dr)
Right	Credit (Cr)

🧮 Transaction Example

When reading the example, note the normal balance of each account and whether the transaction is recorded on the left or right side of the ledger. Assume a business entity performs the following activities:

Purchases $10,000 of inventory from a vendor, on credit.
Transfers the inventory to a customer in exchange for $15,000 of cash.
Pays $10,000 of cash to the vendor for inventory purchased with credit.

Observations

Both sides of the transaction are equal in each case.
For the reader who is scientifically literate but a layperson in accounting: if debits are viewed as positive amounts, credits as negative amounts, and blank squares as zero, then equity = assets + liabilities in each line.
The net impact of the transactions is an increase in cash of $5,000 and an increase in equity of $5,000.
This is reasonable because the company bought inventory for $10,000 and sold it for $15,000, leaving $5,000 as the profit in the business.
The net impact of all transactions is that the owner's equity in the business has increased by $5,000, because it purchased inventory for $10,000 and in turn sold it to an end customer for $15,000.

Double-Entry Bookkeeping: Accounting Study Notes