An HSN code (Harmonised System of Nomenclature) is the internationally standardised number that classifies goods under GST and determines which tax rate applies; services use the parallel SAC codes. As of Aug 2026, businesses with turnover up to ₹5 crore report 4-digit HSN codes on invoices and in GSTR-1, and those above ₹5 crore report 6 digits.
The HSN code is what connects your product to a rate slab. Since GST 2.0 restructured rates to 0/5/18/40 from 22 September 2025, that connection matters more than ever: many items changed slabs, and your product's HSN — not your habit — decides whether you charge 5% or 18%. The GSTR-1 HSN summary is mandatory and portal-validated, so sloppy classification shows up immediately.
The practical exercise is a one-time SKU-to-HSN mapping: list everything you sell, assign the correct code, load it into your billing software, and review it whenever rates change or you add products. If you did this mapping before September 2025, redo the rate column — the codes are the same but many slabs moved. Composite products and kits deserve extra care, since classification disputes cluster there.
The cost of getting it wrong is asymmetric. A wrong HSN pointing to a lower rate means short-paid tax surfacing later as a demand with interest and penalty; pointing to a higher rate means you've overcharged customers and priced yourself out. Buyers also increasingly reject invoices with obviously wrong codes because it complicates their own compliance.
Reviewed to the law in force in FY 2026-27. General information, not advice — confirm the position for your facts before acting.