What does a trial balance check, and which errors can it never detect?
Prepare a trial balance from ledger balances and explain the errors it does and does not reveal
A focused answer to the H2 Principles of Accounting outcome on the trial balance. Listing debit and credit balances, why it should agree, the six errors that do not affect agreement, and what a balanced trial balance does and does not prove.
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What this dot point is asking
SEAB wants you to prepare a trial balance from ledger balances and, just as importantly, to explain its limits: the errors it reveals and the errors it cannot. The trial balance is the bridge between the ledger and the financial statements, and a favourite exam target precisely because students over-trust it. The central insight is that a trial balance is only an arithmetic check that debits equal credits; agreement does not prove the accounts are correct.
The answer
What a trial balance is
A trial balance is a list of every ledger account balance at a date, set out in two columns: debit balances in one, credit balances in the other. Using the debit and credit rules, assets and expenses (and drawings) carry debit balances, while liabilities, capital and income carry credit balances. If the bookkeeping has been done with equal debits and credits throughout, the two column totals must be equal.
Why it should agree
Because every transaction was recorded with a debit and an equal credit, the sum of all debit balances must equal the sum of all credit balances. The trial balance therefore confirms the arithmetical accuracy of the double entry and provides a tidy starting list for preparing the income statement and statement of financial position.
The six errors a trial balance does not reveal
A balanced trial balance is not proof of correctness. Six error types leave the totals equal:
| Error | What happens |
|---|---|
| Omission | Transaction left out entirely (both sides missing) |
| Commission | Right amount, wrong account of the same type |
| Principle | Posted to the wrong class of account (for example capital vs revenue) |
| Original entry | Wrong figure entered, but consistently on both sides |
| Complete reversal | Debit and credit entries swapped |
| Compensating | Two separate errors cancel each other out |
Errors that do unbalance the trial balance include posting only one side, posting different amounts to the two sides, or adding a balance into the wrong column; these create a difference that is then investigated, often via a suspense account.
Examples in context
Example 1. Catching a one-sided posting. A cashier debits bank for a \2,000\. Because this error breaks the equality, the trial balance flags it, and the bookkeeper traces and corrects the missing credit, often by first parking the difference in a suspense account.
Example 2. A hidden error of principle. A business debits the \25,000\ and assets by the same, an error the trial balance can never reveal, which is why other checks are needed.
Try this
Q1. State which side of the trial balance each appears on: rent received, motor vehicles, trade payables. [3 marks]
- Cue. Rent received is income (credit); motor vehicles is an asset (debit); trade payables is a liability (credit).
Q2. A trial balance fails to agree by \900$. Give two errors that could cause this. [2 marks]
- Cue. Posting only one side of a transaction, or posting different amounts to the debit and credit sides (for example \900$ added on one side only or a transposition affecting just one side).
Q3. Explain why an error of commission does not affect the agreement of the trial balance. [3 marks]
- Cue. The correct amount is posted as a debit and a credit, just to the wrong account of the same type, so total debits and credits remain equal and the trial balance still agrees.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksFrom the following balances at December, prepare a trial balance and state the total: Capital \50\,000\; Purchases \45\,000\; Trade receivables \12\,000\; Bank (debit) \7\,000\.Show worked answer →
Assets and expenses are debit balances; liabilities, capital and income are credit balances.
| Account | Debit ($\
| --- | --- | --- |
| Capital | | 50,000 |
| Sales | | 80,000 |
| Purchases | 45,000 | |
| Premises | 60,000 | |
| Trade receivables | 12,000 | |
| Trade payables | | 9,000 |
| Bank | 7,000 | |
| Wages | 15,000 | |
| Total | 139,000 | 139,000 |
Debits = 45\,000 + 60\,000 + 12\,000 + 7\,000 + 15\,000 = \139,000= 50,000 + 80,000 + 9,000 = \. The trial balance agrees at \139,000$.
Markers reward placing each balance on the correct side, correct totals, and an agreed trial balance.
Original5 marksA trial balance agrees, yet the bookkeeper is told several errors exist. Explain three types of error that do not affect the agreement of a trial balance, with an example of each.Show worked answer →
A trial balance only checks that total debits equal total credits, so any error that keeps that equality intact is undetected. Three such errors:
Error of omission. A transaction is left out entirely, so both the debit and credit are missing. Example: a \500$ credit sale never recorded - receivables and sales are both understated, but the balance still agrees.
Error of commission. The correct amount is posted to the wrong account of the same type. Example: a payment to supplier Tan posted to supplier Tang; total payables unchanged, balance agrees.
Error of principle. An item is posted to the wrong class of account. Example: the purchase of a van (asset) debited to motor expenses; debits and credits still equal, so the balance agrees though profit and assets are wrong.
Other undetected errors are errors of original entry, complete reversal, and compensating errors. Markers reward three correctly named error types, an example each, and the explanation that they preserve the debit-credit equality.
Related dot points
- Apply the rules of double-entry bookkeeping to record transactions as debits and credits in the appropriate ledger accounts
A focused answer to the H2 Principles of Accounting outcome on double-entry bookkeeping. The debit and credit rules for the five elements, T-accounts, balancing off, and worked postings of everyday transactions.
- Correct errors using journal entries and a suspense account and restate the effect on profit
A focused answer to the H2 Principles of Accounting outcome on correcting errors. Journal entries for the six error types, when a suspense account is needed, clearing it, and recalculating corrected profit.
- Describe the books of prime entry and the ledger system and explain how source documents flow through them to the accounts
A focused answer to the H2 Principles of Accounting outcome on books of prime entry and the ledgers. Source documents, the journals (sales, purchases, returns, cash, general), posting to the sales, purchases and general ledgers, and the audit trail.
- Prepare control accounts and a bank reconciliation statement and explain how each acts as an independent check
A focused answer to the H2 Principles of Accounting outcome on control accounts and bank reconciliation. The receivables and payables control accounts, reconciling to the personal ledgers, and reconciling the cash book to the bank statement.