Evolution of Section 15(3)(b) of CGST Act: Post‑Supply Discounts and Continuing Ambiguities

The computation of taxable value is the cornerstone of any GST regime. Under the Indian GST law, this task is primarily governed by Section 15 of the CGST Act, 2017 read with the CGST Rules, 2017. The scheme is built around the concept of transaction value—the price actually paid or payable for the supply—along with clearly stated inclusions and exclusions which ultimately determine the base on which GST is levied.

Within this framework, post-supply discounts occupy a uniquely contentious position. These are dealt with in Section 15(3)(b) and relate to reductions in price that are agreed and granted after the original invoice has already been raised. Such discounts are routine in commercial practice—volume rebates, turnover discounts, annual incentives, settlement discounts and promotional schemes are standard features in sectors such as FMCG, automotive, pharmaceuticals, manufacturing, and organised retail.

While they are commercially indispensable, the GST treatment of such post-supply discounts has produced sustained litigation and compliance complexity since July 2017. The legislative and administrative journey of Section 15(3)(b) can be divided into four broad phases:

  1. The original three-condition provision (2017–2024)
  2. The overlay created by Circular 212/6/2024-GST
  3. The 56th GST Council intervention and Circular 251/08/2025-GST plus withdrawal of Circular 212
  4. The statutory amendment through Finance Act 2026, leaving a single operative condition

This article traces that trajectory, analyses the rationale and legal robustness of each change, and highlights the unresolved interpretive issues that still affect the assessee community.

The central issues are:

  • Whether moving from three conditions to one in Section 15(3)(b) is a principled simplification aligned with neutral treatment of discounts in a destination-based GST/VAT system; and
  • Whether the amended framework is self-contained and workable, or whether further statutory and administrative measures are essential to bring certainty to commercial practice.

Valuation Framework Under Section 15 and Placement of Discounts

Transaction Value as the Core Principle

Section 15(1) of the CGST Act stipulates that the value of a supply of goods or services or both shall be the transaction value, i.e., the price actually paid or payable for the said supply, where:

  • Supplier and recipient are not related; and
  • Price is the sole consideration.

This is a conscious break from the erstwhile Central Excise regime, which relied on vague standards like “normal price” or “assessable value” and produced heavy litigation regarding what a hypothetical arm’s length price should have been.

Section 15(2) lists the mandatory additions to transaction value, including:

  • Taxes and duties other than GST
  • Amounts incurred by recipient but liable to be borne by supplier
  • Incidental expenses charged by supplier
  • Interest or late fee for delayed payment
  • Subsidies directly linked to price

Section 15(3) then provides for exclusions by recognising discounts in two distinct buckets:

  • Section 15(3)(a): discounts known at or before supply and reflected in the invoice (pre-supply discounts); and
  • Section 15(3)(b): discounts granted after the supply (post-supply discounts).

Structural Distinction: Pre-Supply vs Post-Supply Discounts

The legal treatment differs because information and timing differ.

  • Pre-supply discounts:
    These are pre-negotiated. The value already stands reduced in the tax invoice. GST is charged on the discounted value. ITC to the recipient is aligned with actual GST charged. No further compliance is needed; no mismatch arises in returns.

  • Post-supply discounts:
    Here, the initial invoice is issued at full contractual price. GST is paid on that higher value, and the recipient avails ITC accordingly. Later, when a discount is granted, there is a retrospective change in consideration. To preserve tax neutrality, two corresponding adjustments are needed:

    1. Reduction of supplier’s output tax liability; and
    2. Reversal of proportionate ITC by the recipient.

Section 15(3)(b) is the pivot around which this symmetric reduction is intended to operate.

Original Section 15(3)(b): Three Conditions and Their Structural Weaknesses

The Original Three-Limb Test

From 1st July 2017, the original Section 15(3)(b) allowed exclusion of post-supply discounts from taxable value only when the following three conditions were jointly satisfied:

  1. Pre-agreement requirement
    The discount must be “established in terms of an agreement entered into at or before the time of such supply.”

  2. Invoice-linkage requirement
    The discount must be “specifically linked to relevant invoices.”

  3. ITC reversal requirement
    The recipient must reverse the ITC attributable to such discount.

The Third-Party Dependency Problem

The third condition was the most structurally infirm. It effectively made reduction of the supplier’s GST liability contingent on an act of the recipient.

Key issues:

  • The supplier has no direct statutory right to force the recipient to reverse ITC.
  • There is no built-in mechanism in the GST portal to cross-verify whether reversal was actually done.
  • As long as the recipient does not reverse ITC, the supplier’s ability to reduce output tax remains in limbo.

On the ground, this led to:

  • Frequent disputes between suppliers and recipients over the timing and obligation to reverse ITC.
  • Situations where the supplier issued a credit note and reduced the commercial value, but was still unable to reduce its tax liability due to non-cooperation or delay by the recipient.
  • A verification vacuum—no system-level link between credit note issued by supplier and ITC reversal by recipient.

Pre-Agreement Requirement vs Commercial Reality

The pre-agreement condition sat poorly with Indian commercial practice.