How is GST calculated?
Adding GST: GST = Base price × GST rate ÷ 100, and Total = Base price + GST.
Removing GST from an inclusive price: Base price = Total × 100 ÷ (100 + GST rate).
CGST, SGST and IGST
For sales within the same state, GST is split equally into CGST (Central) and SGST (State). For inter-state sales, the full amount is charged as IGST. For example, on an 18% service sold within Odisha, you charge 9% CGST + 9% SGST; sold to a client in Maharashtra, you charge 18% IGST.
GST on digital marketing and website services
In India, digital marketing, website design, SEO and software development services generally attract 18% GST (SAC 998361/998314). Always confirm the applicable rate with your chartered accountant.
GST rates after the September 2025 changes
From 22 September 2025, the GST Council moved most goods and services to two main rates, 5% and 18%, plus a 40% rate for luxury and sin goods. Special rates such as 0%, 0.25% and 3% continue for certain items. We have kept 12% and 28% in the tool for working out older invoices. Always confirm the rate for your specific HSN or SAC code with your CA or on the official CBIC website.
GST inclusive and exclusive: worked examples
| Question | Formula | Answer |
|---|---|---|
| Add 18% to ₹10,000 | 10,000 × 1.18 | ₹11,800 |
| Remove 18% from ₹11,800 | 11,800 ÷ 1.18 | ₹10,000 |
| Add 5% to ₹2,000 | 2,000 × 1.05 | ₹2,100 |