Double-Entry Foundations and the Accounting Equation

Learning objectives

By the end of this chapter you should be able to:

• Explain how transactions change assets, liabilities and equity, and keep the accounting equation in balance.
• Apply debit and credit rules to prepare accurate journal entries for common business events.
• Post entries to T-accounts, calculate closing balances, and explain what those balances represent.
• Prepare a trial balance and use it to check the arithmetic accuracy of the ledger.
• Interpret how entries flow into the statement of financial position and the statement of profit or loss.
• Identify frequent misclassifications (cash vs credit, capital vs revenue, owner vs business, income vs liabilities).

Overview & key concepts

Double-entry bookkeeping records each transaction with equal debits and credits. This keeps the accounting records internally consistent and preserves the accounting equation:

Assets = Liabilities + Equity

Each transaction changes at least two accounts, but the total effect always keeps the equation in balance.

To reduce confusion early on, treat “cash” as a general label for money held by the business. In practice, many entries are made through Bank (cash at bank), even if the business also holds physical cash.

The accounting equation

The accounting equation explains why double-entry works. Every transaction changes at least two items in the equation, but the equality must always remain true.

Example (credit purchase of equipment):

• Equipment (asset) increases
• Trade payables (liability) increases
  Both sides increase by the same amount.

Mapping the equation to common ledger accounts

• Assets: Bank, Trade receivables, Inventory, Equipment
• Liabilities: Trade payables, Loan payable, Deferred income (unearned revenue)
• Equity: Owner’s capital, Drawings (and the accumulated retained profit/loss)

In double-entry, every transaction affects at least two of these categories, so the equation stays balanced.

Double-entry system

A double-entry is a paired recording:

• Debit (Dr) one or more accounts
• Credit (Cr) one or more accounts
• Total debits must equal total credits

Debit/credit is not “plus/minus”. It is the method used to record increases and decreases in different types of account.

Journal entries

A journal entry is the first formal record of a transaction. A good journal entry has:

• Date
• Accounts debited and credited
• Amounts
• A short narrative explaining the business event

Example (cash sale):

• Dr Bank
• Cr Sales revenue

If the sale is on credit:

• Dr Trade receivables
• Cr Sales revenue

Ledger and T-accounts

The ledger contains all accounts used by the business. A T-account is a learning format that shows:

• Debits on the left
• Credits on the right
• The closing balance carried down

Balancing a T-account means calculating the net difference between total debits and total credits and stating whether the account ends with a debit balance or a credit balance.

Trial balance

A trial balance checks whether the ledger balances add up: the total of debit balances should equal the total of credit balances. This helps spot errors that break the double-entry principle (for example, posting only one side of a transaction).

However, some mistakes won’t show up. If you record the wrong account but still post equal debits and credits—such as Dr Repairs expense / Cr Bank for a vehicle purchase—the trial balance can still balance even though the classification is wrong. A transaction that is not recorded at all also creates no imbalance because nothing was posted.

Core theory and frameworks

Recognising transactions: cash vs credit

Transactions are recorded when they occur (i.e., when the business earns income or incurs costs), not simply when cash moves.

• A cash receipt is not always income (it could be a loan, capital introduced, or collection of a receivable).
• A cash payment is not always an expense (it could settle a payable, purchase an asset, or be a withdrawal by the owner).

Key distinction

• Credit sale: revenue is recorded now, cash later → a receivable arises.
• Advance receipt from a customer: cash is received now, but goods/services are provided later → a liability arises.

A reliable way to choose Dr/Cr

Step 1: Identify the account type (asset, liability, equity, income, expense).
Step 2: Decide whether the account is increasing or decreasing.

Use these increase rules:

• Assets and expenses increase on the debit side.
• Liabilities, equity and income increase on the credit side.

For decreases, use the opposite side.

A quick sense-check is to ask: What is the business receiving, and what is it giving up? Then choose the appropriate accounts and apply the increase rules.

Operating expenses: timing patterns

In practice, expense entries depend on timing. There are three common cases:

• Pay and consume now: Dr Expense; Cr Bank
• Consume now, pay later (accrual): Dr Expense; Cr Payable/Accrued expense
• Pay now, consume later (prepayment): Dr Prepayment; Cr Bank, then as the benefit is used: Dr Expense; Cr Prepayment

Inventory and cost of sales

Sales revenue and cost of sales are recorded separately:

• Sales revenue records the selling price (income).
• Cost of sales records the cost of inventory sold (expense).
• Inventory reduces when goods are sold.

Two approaches are common:

• Perpetual inventory system: record cost of sales and reduce inventory at the time of each sale.
• Periodic inventory system: calculate cost of sales at period end using opening inventory + purchases − closing inventory.

Many questions present transactions in a way that suits perpetual-style entries, but you may also see periodic-style adjustments depending on the information provided.

Deferred income (unearned revenue)

Sometimes a customer pays before the business has delivered the goods or provided the service. In that situation, the business has received cash but has not yet completed what the customer is paying for.

Until delivery (or completion of the service) happens, the amount received is shown as a liability because the business still owes goods or services. When delivery takes place, the liability is reduced and income is recognised.

Example (customer pays 600 in advance for services):

• On receipt: Dr Bank 600; Cr Deferred income 600
• When services are provided: Dr Deferred income 600; Cr Revenue 600

Notes payable and interest

When a loan is received:

• Dr Bank (or other asset received)
• Cr Loan payable (liability)

Interest is recognised over time:

• Dr Interest expense
• Cr Bank (if paid) or Interest payable (if accrued)

Allowance for receivables (irrecoverable / doubtful debts)

At this level, treat an allowance as an estimate made at period end to show receivables at the amount the business expects to collect. It reflects the fact that some credit customers may not pay.

Typical period-end entry to raise or increase the allowance:

• Dr Irrecoverable debts expense (or bad debt expense)
• Cr Allowance for receivables

If a specific customer balance is later written off as irrecoverable:

• Dr Allowance for receivables
• Cr Trade receivables

Some simpler systems use the direct write-off method (Dr Bad debt expense; Cr Trade receivables) when a balance is confirmed irrecoverable. The allowance approach is generally preferred for period-end reporting because it presents receivables at the amount expected to be collected.

Equity transactions: capital, drawings/dividends, retained results

Owner-related movements are not income or expenses of the business.

• Capital introduced increases equity: Dr Bank; Cr Owner’s capital
• Drawings/dividends reduce equity: Dr Drawings (or Dividends); Cr Bank
• Profit or loss affects equity through retained results via the year-end closing process, not through capital introduced.

Worked example

Narrative scenario

ABC Retailers is a small retail business. At 1 February 2026 the business already existed and had the following opening balances:

• Trade receivables: 1,000
• Equipment (cost): 5,000
• Owner’s capital (balancing figure): 6,000

During February 2026 the following transactions occurred:

1. 1 Feb: The owner invested 10,000 into the business bank account.
2. 3 Feb: Purchased inventory worth 5,000 on credit.
3. 5 Feb: Made a cash sale of 2,000.
4. 7 Feb: Paid 1,500 to a supplier for the earlier credit purchases.
5. 10 Feb: Received 1,000 from a customer for a previous credit sale (the opening receivable).
6. 12 Feb: Paid rent of 800 by bank transfer.
7. 15 Feb: Paid 300 by bank transfer for office supplies (treated as an expense).
8. 18 Feb: Sold goods on credit for 1,200.
9. 20 Feb: Received a loan of 5,000, deposited into the bank.
10. 25 Feb: Paid 200 for utilities by bank transfer.
11. 28 Feb: The owner withdrew 500 for personal use.
12. 28 Feb: Recorded depreciation of 100 on equipment.

Additional information (given for this exercise):
Goods are sold at a 40% gross margin on selling price. For the purpose of this exercise, treat cost of sales as 60% of sales value. This is a simplifying assumption and not a general method of inventory valuation in practice.

Required

1. Prepare journal entries for each transaction (including cost of sales).
2. Post entries to T-accounts and balance them.
3. Prepare a trial balance as at 28 February 2026.
4. Explain the impact on the financial statements.

Solution

1) Journal entries

Opening balances (1 Feb 2026)

• Dr Trade receivables 1,000
• Dr Equipment (cost) 5,000
• Cr Owner’s capital 6,000

1 Feb – Capital introduced

• Dr Bank 10,000
• Cr Owner’s capital 10,000

3 Feb – Inventory purchased on credit

• Dr Inventory 5,000
• Cr Trade payables 5,000

5 Feb – Cash sale (revenue)

• Dr Bank 2,000
• Cr Sales revenue 2,000

5 Feb – Cost of sales (60% × 2,000 = 1,200)

• Dr Cost of sales 1,200
• Cr Inventory 1,200

7 Feb – Payment to supplier

• Dr Trade payables 1,500
• Cr Bank 1,500

10 Feb – Receipt from customer (settlement of opening receivable)

• Dr Bank 1,000
• Cr Trade receivables 1,000

12 Feb – Rent paid

• Dr Rent expense 800
• Cr Bank 800

15 Feb – Office supplies paid

• Dr Office supplies expense 300
• Cr Bank 300

18 Feb – Credit sale (revenue)

• Dr Trade receivables 1,200
• Cr Sales revenue 1,200

18 Feb – Cost of sales (60% × 1,200 = 720)

• Dr Cost of sales 720
• Cr Inventory 720

20 Feb – Loan received

• Dr Bank 5,000
• Cr Loan payable 5,000

25 Feb – Utilities paid

• Dr Utilities expense 200
• Cr Bank 200

28 Feb – Owner withdrawal

• Dr Drawings 500
• Cr Bank 500

28 Feb – Depreciation

• Dr Depreciation expense 100
• Cr Accumulated depreciation 100

2) Closing balances from T-accounts

Assets

• Bank (Dr): 14,700
• Trade receivables (Dr): 1,200
• Inventory (Dr): 3,080
• Equipment at cost (Dr): 5,000

Liabilities

• Trade payables (Cr): 3,500
• Loan payable (Cr): 5,000

Equity

• Owner’s capital (Cr): 16,000
• Drawings (Dr): 500

Income

• Sales revenue (Cr): 3,200

Expenses

• Cost of sales (Dr): 1,920
• Rent expense (Dr): 800
• Office supplies expense (Dr): 300
• Utilities expense (Dr): 200
• Depreciation expense (Dr): 100

Contra asset

• Accumulated depreciation (Cr): 100

3) Trial balance as at 28 February 2026

Account	Dr	Cr
Bank	14,700	-
Trade receivables	1,200	-
Inventory	3,080	-
Equipment (cost)	5,000	-
Trade payables	-	3,500
Loan payable	-	5,000
Owner’s capital	-	16,000
Sales revenue	-	3,200
Cost of sales	1,920	-
Rent expense	800	-
Office supplies expense	300	-
Utilities expense	200	-
Depreciation expense	100	-
Drawings	500	-
Accumulated depreciation	-	100
Totals	27,800	27,800

4) Impact on the financial statements

Statement of financial position (end of February)

• Assets: bank (14,700), receivables (1,200), inventory (3,080), equipment at cost (5,000) less accumulated depreciation (100).
• Liabilities: trade payables (3,500) and loan payable (5,000).
• Equity: owner’s capital (16,000) reduced by drawings (500), with the period’s profit/loss transferred into retained results through the closing process.

Statement of profit or loss (February performance)

• Revenue: 3,200
• Cost of sales: 1,920 → gross profit: 1,280
• Expenses: rent 800, utilities 200, office supplies 300, depreciation 100 (total 1,400)
• Net result: loss of 120

This demonstrates that cash can increase (through capital introduced and borrowing) even when the period’s trading result is a loss.

Common pitfalls and misunderstandings

• Treating every cash receipt as income (it may be a loan, capital introduced, or collection of receivables).
• Treating every cash payment as an expense (it may settle payables, purchase an asset, or be drawings/dividends).
• Omitting cost of sales entries (or the period-end calculation), which misstates profit and inventory.
• Mixing owner transactions into income/expenses (capital and drawings are equity movements).
• Assuming a balanced trial balance guarantees correct accounting (classification errors or a transaction not recorded at all may still exist).
• Misclassifying capital vs revenue spending (future benefit vs day-to-day running costs).

Summary and further reading

Double-entry bookkeeping keeps the accounting equation in balance by recording every transaction with equal debits and credits. Journal entries capture transactions, ledgers and T-accounts accumulate them into balances, and the trial balance provides an arithmetic check before preparing financial statements.

These foundations support later topics such as adjustments (accruals, prepayments, depreciation, allowances for receivables), reconciliations, and error correction.

FAQ

Why is double-entry bookkeeping important?

It forces transactions to be recorded in a balanced way and creates ledger balances that can be summarised into financial statements. It also helps detect arithmetic errors because total debits must equal total credits.

How does the accounting equation connect to the statement of financial position?

The statement of financial position is a structured presentation of the accounting equation. Every transaction changes assets, liabilities and/or equity, but the equality must remain true after each entry.

What are common mistakes when preparing journal entries?

Typical errors include confusing cash receipts with revenue, mixing owner transactions into income/expenses, omitting cost of sales, and posting to the wrong account while still keeping debits equal to credits.

How are errors corrected?

A clear method is to reverse the incorrect entry and then post the correct entry. This keeps an audit trail and restores correct balances.

What do T-accounts add beyond journal entries?

They show how multiple entries build up a running balance in each account, making it easier to check whether cash, receivables, payables and inventory balances are sensible.

Summary (Recap)

This chapter explains the logic and mechanics of double-entry bookkeeping. Transactions are analysed using the accounting equation and recorded as balanced journal entries. Those entries are posted into ledger accounts (often shown as T-accounts), producing balances that feed into a trial balance. The worked example demonstrates how cash, credit, inventory, cost of sales, expenses, financing and owner movements are recorded and how they affect both financial position and performance.

Glossary

Accounting equation
A relationship showing that business resources are funded by obligations and owners’ interest: Assets = Liabilities + Equity.

Accumulated depreciation
A contra asset account that reduces the carrying amount of a non-current asset by collecting depreciation recorded to date.

Allowance for receivables
A contra asset used to reduce trade receivables to the amount expected to be collected, based on an estimate of irrecoverable amounts.

Credit (Cr)
An entry on the right side of an account. It increases liabilities, equity and income, and decreases assets and expenses (depending on the account).

Debit (Dr)
An entry on the left side of an account. It increases assets and expenses, and decreases liabilities, equity and income (depending on the account).

Deferred income (unearned revenue)
Amounts received from customers before goods are delivered or services are provided. Recognised as a liability until delivery or service completion.

Drawings
Withdrawals by the owner for personal use. Drawings reduce equity and are not an expense of the business.

Journal entry
A dated record showing the debits and credits for a transaction, typically supported by a short narrative.

Ledger
The full set of accounts where transactions are accumulated and balances are maintained.

Trial balance
A list of ledger balances at a point in time. Total debits should equal total credits if entries are arithmetically consistent.