What it means
The ISAs cover the full arc of an audit, from accepting the engagement and assessing risk through gathering evidence to forming and wording the final opinion. Each standard is numbered, so auditors refer to specific requirements such as ISA 315 on identifying risk or ISA 700 on the auditor's report.
They matter to management because they set the terms of engagement. When an auditor insists on attending your stock count, writing to your lawyers, or testing journal entries posted late at night, that is a specific ISA requirement rather than an arbitrary demand.
The standards are risk based rather than a checklist of every transaction. Auditors are required to understand your business and its controls, decide where a material error is most likely, and concentrate their testing there, which is why two companies of similar size can face very different audits.
A central concept running through the ISAs is materiality, the size of misstatement that would change the decisions of someone reading the accounts. It is set as a monetary threshold at the planning stage, reduced to a lower figure called performance materiality for testing purposes, and revisited if circumstances change.
Two clarifications are worth noting. ISAs govern audits, not the preparation of the accounts themselves, which follows a separate accounting framework, and the same three letters also stand for the UK Individual Savings Account, a tax free savings wrapper with no connection to auditing whatsoever.
In practice
Real-world examples.
Example
A distribution company is surprised when its auditors insist on observing the year end stock count at three warehouses rather than one. The engagement partner explains that ISA 501 requires attendance where inventory is material, and inventory is 40% of the balance sheet.
Example
A software business receives a long list of questions about revenue recognised in the final two weeks of the year. The testing reflects the standard presumption that revenue recognition carries a risk of fraud, so the auditor must design specific procedures to address it.
Example
A group finance director is asked to provide a written representation letter confirming that all liabilities have been disclosed. It feels like a formality, but the auditor cannot complete the file without it, since written representations are a required form of evidence.
Think of it
“ISA is international auditing standards-the global rules for conducting audits.
Formula
Calculation
Planning materiality is commonly set as a percentage of a chosen benchmark, most often profit before tax, revenue or total assets
An audit firm is planning the audit of a manufacturer with revenue of $80,000,000 and profit before tax of $4,000,000. The engagement partner selects profit before tax as the benchmark and applies a 5% rate, giving planning materiality of $4,000,000 x 0.05 = $200,000.
Performance materiality is then set at 75% of that figure to allow room for undetected errors adding up, so $200,000 x 0.75 = $150,000. Individual balances and transactions are tested against this lower threshold rather than against the headline number.
Finally, the clearly trivial threshold, below which misstatements are not even accumulated for reporting, is set at 5% of planning materiality: $200,000 x 0.05 = $10,000. So a $6,000 error is ignored, a $40,000 error is logged and reported to the audit committee, and an uncorrected total approaching $200,000 would put the audit opinion at risk.Case study
Seen in the real world.
The following is a fictional and illustrative case. Kestrel Marine Supplies, an invented ship chandler with revenue of $52,000,000, had used the same small audit firm for a decade and treated the annual visit as a two week formality. When it was acquired by a listed group, the new auditors applied the ISAs far more rigorously.
Planning materiality was set at $180,000, and the new team tested controls over the manual journals that Kestrel's finance manager had been posting at each month end to smooth reported margin. The journals were individually below the old firm's threshold but accumulated to $310,000 across the year.
Because the total exceeded materiality and could not be supported, the invented auditors required the accounts to be restated before signing an unmodified opinion. In this illustrative example, nothing about the business had changed; only the rigour with which the standards were applied.
Watch out
Common mistakes.
- Assuming an audit under the ISAs checks every transaction, when the standards explicitly require a risk based, sample driven approach.
- Treating an unmodified audit opinion as a guarantee that no fraud exists, when the opinion only offers reasonable assurance that the accounts are free from material misstatement.
- Confusing International Standards on Auditing with the accounting rules used to prepare the accounts, which are a separate framework entirely.
Questions
People also ask.
Who writes the ISAs?
They are issued by an international auditing and assurance standards board, and individual countries then adopt them, sometimes adding local requirements on top.
Does materiality have a fixed percentage?
No, the standards require professional judgement, though 5% of profit before tax and around 0.5% to 1% of revenue or total assets are widely used starting points.
Do small companies have to be audited under the ISAs?
Only if an audit is required or requested at all, but when one is performed the same standards apply, scaled to the size and complexity of the entity.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%