GST valuation rules define transaction value, inclusions, discounts, and prescribed methods for related-party and notified supplies. The value of a supply of goods or services or both is ordinarily the transaction value, being the price actually paid or payable where the supplier and recipient are not related and the price is the sole consideration. The taxable value includes specified taxes, incidental expenses, delayed payment charges and price-linked subsidies, while eligible discounts are excluded if properly recorded or supported by a credit note and reversal of input tax credit. Where value cannot be determined under the main rule, or for notified supplies, valuation must follow the prescribed method.