GST Explained for Small Business Owners
You don't need to understand the entire GST Act to run your business correctly — just the handful of concepts that actually show up on your invoices every day.
GST can feel like an enormous, legalistic system from the outside, but the day-to-day mechanics that a small business actually deals with come down to a handful of ideas: which slab applies, how to split the tax, and how add/remove GST correctly on an invoice.
The slabs you'll actually encounter
Most goods and services fall into one of a small set of common slabs — 0%, 5%, 12%, 18%, or 28% — depending on the category. If you're unsure which applies to what you sell, that's worth confirming once with a GST practitioner or the official rate schedule; getting it wrong on every invoice compounds fast.
CGST + SGST vs IGST — the one distinction that trips people up
If you're selling to a customer in the same state, the GST amount splits equally into CGST (central government's share) and SGST (state government's share) — so an 18% rate becomes 9% CGST + 9% SGST on the invoice. If you're selling to a customer in a different state, the full amount is charged as IGST instead, with no split. Getting this wrong on an invoice is one of the most common small-business GST errors.
Adding vs removing GST
If you're quoting a base price and need to add tax on top, that's straightforward multiplication. But often you're handed an MRP or a final client-approved amount and need to work backward to find the base price and tax component within it — a different formula, and one people frequently get wrong by just taking a straight percentage off the final price instead of using the correct reverse formula.
Do this now
Use the GST Calculator for both directions — adding GST to a base price, or extracting the base price and GST from a final amount — and to get the correct CGST/SGST or IGST split depending on whether the sale is intra-state or inter-state.