IFRS 2.16–18 requires that the fair value of options and other equity instruments granted to employees be estimated using an option-pricing model that accounts for: the exercise price, the option life, the current share price, the expected volatility of the share price, dividends expected on the shares, and the risk-free interest rate over the option term. Grant-date fair value is determined once and is never revised.
Employee share options cannot be valued using intrinsic value alone (share price minus exercise price) because intrinsic value ignores time value — the probability that the option will move deeper in-the-money before expiry. IFRS 2 requires fair value, which captures both intrinsic value and time value. Intrinsic value measurement is only a permitted fallback where fair value cannot be reliably estimated (IFRS 2.24), which in practice applies only to unlisted entities with complex equity structures.
Black-Scholes is the default model for European-style options (exercisable only at expiry) and for options where early exercise behaviour is not material.