Negligence · Breach of duty

Wyong Shire Council v Shirt: the calculus of negligence

How do you decide whether a defendant who owed a duty of care breached it? Wyong Shire Council v Shirt (1980) 146 CLR 40 gave the common law answer, and its structure still shapes the statutory tests under the civil liability Acts.

Last updated 9 November 2026

In short

  • At common law, a risk is foreseeable unless it is far-fetched or fanciful.
  • Mason J’s calculus weighs the magnitude and probability of harm against the burden of precautions and the defendant’s other responsibilities.
  • Section 5B of the Civil Liability Act 2002 (NSW) and equivalents replaced "not far-fetched or fanciful" with "not insignificant", and restate the calculus.

The case

A water skier was injured after relying on a council sign reading "deep water" in a shallow lake. The High Court upheld a finding of negligence against the council. Read it in the case index: Wyong Shire Council v Shirt [1980] HCA 12.

Mason J’s calculus

Mason J said that the tribunal of fact must first ask whether a reasonable person in the defendant’s position would have foreseen that the conduct involved a risk of injury to the plaintiff or a class of persons including the plaintiff. If so, it must decide what a reasonable person would do in response, considering:

  • the magnitude of the risk;
  • the degree of probability of its occurrence;
  • the expense, difficulty and inconvenience of taking alleviating action; and
  • any other conflicting responsibilities the defendant may have.

A risk that is not far-fetched or fanciful is foreseeable, even if it is extremely unlikely to occur.

The civil liability Acts

After the 2002 Review of the Law of Negligence, the States and Territories enacted civil liability legislation. In New South Wales, s 5B of the Civil Liability Act 2002 (NSW) provides that a person is not negligent in failing to take precautions unless the risk was foreseeable, the risk was not insignificant, and a reasonable person would have taken those precautions. Section 5B(2) lists considerations that track the Shirt calculus.

Frequently asked questions

What is the calculus of negligence?

The weighing exercise from Mason J’s judgment in Wyong Shire Council v Shirt: the magnitude and probability of the risk against the burden of precautions and the defendant’s other responsibilities.

Is "far-fetched or fanciful" still the test?

Not where civil liability legislation adopts the "not insignificant" test, as s 5B of the NSW Act does. The common law test still governs where the legislation does not apply, including in the Northern Territory, whose Act has no equivalent breach provision, and for claims the Acts exclude.

Sources

General information, not legal advice. See our editorial policy for how this page is sourced and reviewed, and how to report an error.

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