Value of supply rules define taxable value under GST, including additions, exclusions, and discount treatment. Value of supply is the transaction value-the price actually paid or payable when supplier and recipient are not related and price is the sole consideration. Taxable value includes separately charged statutory levies (excluding GST and its compensation levy), costs incurred by recipient on supplier's behalf, incidental expenses (commission, packing), amounts charged for supplier's acts, interest or penalties for delayed payment, and price-linked subsidies received by the supplier. Discounts recorded on invoice or contractually pre-established and followed by reversal of corresponding input tax credit are excluded. Prescribed alternate valuation methods and notified classes of supplies apply where transaction value cannot be determined.