Transaction value determines taxable supply value, incorporating specified charges and excluding authorised discounts. Value of supply is the transaction value: the price actually paid or payable where parties are not related persons and price is sole consideration. The value includes separately charged non-GST taxes, amounts the supplier is liable for but borne by recipient, incidental expenses (commission, packing), charges for acts by supplier at or before delivery, interest or penalties for late payment, and subsidies directly linked to price received by supplier. Discounts recorded on invoice or post-supply discounts under pre-existing agreement with reversal of input tax credit are excluded. Where transaction value is inapplicable, prescribed valuation methods or notified methods apply.