Every audit involves a number that most clients never see and that determines almost everything about the work: how much testing happens, which balances get looked at, what the fee is, and whether an error you made in March ends up in a conversation with your board in February.
That number is materiality, and it is worth understanding.
What it actually means
Materiality is the point at which an error or omission would be likely to change the decision of someone reading the financial statements. Below that point, the statements still give a true and fair view even though they contain mistakes.
This offends people the first time they hear it. The accounts are wrong, and the auditor is signing them anyway. But the alternative is an audit that chases every penny, which would cost a multiple of what anyone currently pays and tell readers nothing they did not already know.
How it is set
There is no formula in the standards, which surprises people. There are conventions.
An auditor picks a benchmark that reflects what readers of your accounts care about, then applies a percentage. Profit before tax is common for a trading business, with something in the region of five to ten per cent. Revenue is used where profit is volatile or near breakeven, at a much lower percentage. Total assets is used for asset-holding entities and investment vehicles.
The choice of benchmark is a judgement and it matters more than the percentage. A business at breakeven that has materiality set against profit ends up with a very small number and a very expensive audit, which is why a sensible auditor will move to a different benchmark and explain why.
The two numbers underneath it
Overall materiality is not the number used in testing. Two others do the real work.
Performance materiality is lower, often somewhere between half and three quarters of overall materiality. It exists because lots of small errors can add up to one large one, so testing is performed to a tighter threshold than the one used to judge the final result. This is the figure that actually drives sample sizes.
The trivial threshold is lower again, typically a small percentage of overall materiality. Errors below it are not even accumulated. Above it, they go on a schedule of unadjusted differences that is presented to the board at completion, whether or not they are individually significant.
When size stops mattering
Some errors are material regardless of amount. Auditors call these qualitatively material, and they are the ones that catch people out.
Anything involving a director. Related party transactions. An error that turns a profit into a loss or vice versa, or that moves you from one side of a covenant to the other. Anything touching fraud, however small. Disclosures required by law. An item that changes a reported figure management has publicly drawn attention to.
A thousand pound error can be material if it is a thousand pounds paid to a director and not disclosed. This is the part of materiality that cannot be reasoned about numerically, and it is where most difficult completion conversations come from.
What this means for you
Three practical things.
A falling profit makes your audit bigger, not smaller. If you have had a difficult year, expect more testing and budget for it, because materiality fell with the result.
Fixing small errors before fieldwork is worth more than it looks. Every item above the trivial threshold goes on a schedule that your board sees, and a long schedule invites questions about the control environment even when every individual item is tiny.
Never use the threshold as a target. Auditors are explicitly alert to error that clusters just below materiality, and the response is to lower the threshold and widen the testing. The accounting is also simply better if you correct what you find.
Ask the question
Ask your auditor at planning what benchmark they are using, what the percentage is, and what performance materiality works out at. It is information you are entitled to, it tells you where the audit effort is going, and the answer occasionally reveals that the benchmark no longer suits the business. That conversation is much cheaper in October than in February.