Section 15 CGST Act explained: this guide covers what Section 15 CGST Act means, who it applies to, the step-by-step process, documents required, fees, due dates and penalties in India — so you can stay compliant with confidence and avoid costly mistakes.
Section 15 — What Amount Does GST Apply On?
Section 15 determines the value on which GST is calculated. The default is "transaction value" — the price actually paid or payable for the supply. But Section 15 adds specific inclusions that many businesses miss, and provides rules for discounts that can reduce the value.
Transaction Value — The Starting Point
Transaction value = the price actually paid or payable for the supply, where the supplier and recipient are NOT related persons and price is the SOLE consideration. If either condition fails (related parties, or non-monetary consideration), valuation rules under Chapter IV of CGST Rules apply instead.
Mandatory Inclusions in Value — Section 15(2)
The following MUST be added to the transaction value (even if charged separately):
(a) Taxes, duties, cesses under any law other than GST: Custom duty on imports is INCLUDED in the value for IGST calculation. Excise on petrol (if ever brought under GST) would be included. But CGST/SGST/IGST themselves are NOT included (tax is not on tax).
(b) Amount that the supplier is liable to pay but is paid by the recipient: If buyer pays insurance on goods on behalf of the seller, that amount is ADDED to the supply value. The logic: the true consideration is higher than the invoice price.
(c) Incidental expenses charged by supplier: Packing, commission, or any other charge that the supplier charges in addition to the basic price. These are part of the consideration and must be included.
(d) Interest, late fee, penalty for delayed payment: If you charge your customer interest for late payment of invoice, that interest is ADDITIONAL consideration for the original supply and is subject to GST at the same rate as the original supply. This catches many businesses — interest on receivables is taxable.
(e) Subsidies directly linked to price (except government subsidies): If a third party pays a subsidy to the supplier linked to the supply price, the subsidy is added to the transaction value. Government subsidies linked to price are excluded by notification.
Discounts — How to Reduce Value Legally
Section 15(3)(a) — Discount BEFORE supply: If the discount is given BEFORE or AT the time of supply AND is recorded on the invoice, it reduces the transaction value. Example: List price Rs. 1,000, 10% discount = invoice shows Rs. 900. GST on Rs. 900. Simple and clean.
Section 15(3)(b) — Discount AFTER supply: Post-sale discount (volume discount, year-end rebate) reduces the transaction value ONLY if: (i) it was established in terms of an agreement before/at the time of supply, AND (ii) the discount can be specifically linked to relevant invoices, AND (iii) the recipient reverses ITC proportionate to the discount. If ANY condition fails, the discount CANNOT reduce the value. Supplier issues credit note, recipient reverses ITC.
Common problem: Ad-hoc year-end discounts given without pre-existing agreement do NOT reduce GST value — even if credit notes are issued. The supplier still owes GST on the original amount, and the buyer must reverse ITC.
Valuation for Related Party Transactions
If supplier and recipient are related (holding-subsidiary, same group, relative as defined in the Act), transaction value is accepted ONLY if it equals the open market value. If lower, the value for GST purposes is:
(a) Open market value (Rule 28), or
(b) Value of like kind and quality supply, or
(c) Cost + 10% markup (Rule 30), or
(d) Best judgment (Rule 31).
Exception: if the recipient can claim full ITC on the supply, then the value declared in the invoice is accepted even if below market value (Rule 28, second proviso). This is a huge relief for corporate groups — inter-company supplies where both parties have full ITC eligibility do not need arm's-length valuation.
Calculation Examples
Example 1 — Inclusions: Machinery sold for Rs. 10 lakh + packing Rs. 50,000 + transit insurance Rs. 20,000 + late delivery penalty received Rs. 10,000. Value of supply = Rs. 10,80,000. GST at 18% = Rs. 1,94,400.
Example 2 — Pre-supply discount: MRP Rs. 500, trade discount 20% = Rs. 400 on invoice. GST at 12% on Rs. 400 = Rs. 48. Total invoice: Rs. 448.
Example 3 — Post-supply discount without agreement: Supplier gives Rs. 2 lakh year-end rebate to a distributor. No prior written agreement. Supplier issues credit note. But since condition (i) of Section 15(3)(b) fails (no pre-existing agreement), the Rs. 2 lakh CANNOT reduce GST value. Supplier has already paid GST on the original amount and cannot claim refund on credit note. Distributor need not reverse ITC. The credit note reduces commercial liability but NOT GST liability.