How to calculate GST in India
GST (Goods and Services Tax) is added to most goods and services. There are two ways it appears on an invoice:
- Price excludes GST (most business-to-business invoices): you add the tax on top. Total = Amount × (1 + rate / 100).
- Price includes GST (most retail bills): the tax is already inside the price. Base = Amount / (1 + rate / 100) and GST = Amount - Base.
GST slab rates at a glance
| Rate | Typical items |
|---|---|
| 0% | Grains, fruits, vegetables, milk, basic books |
| 0.25% | Rough diamonds, some rare earths |
| 3% | Gold, silver, unsorted precious metals |
| 5% | Staple foods, restaurant (non-AC), transport |
| 12% | Electronics, furniture, processed food |
| 18% | Most services, mobile phones, restaurants (AC) |
| 28% | Luxury cars, tobacco, aerated drinks, AC units |
CGST + SGST vs IGST
Inside a state, GST is split into two halves: CGST (Central) and SGST (State), each around half the bracket rate. Between two states, you pay a single IGST at the full rate. In both cases the combined tax is the same, so the calculator above works for every scenario.
Quick examples
A Rs 10,000 service bill at 18%: GST = Rs 1,800, total = Rs 11,800. A Rs 1,18,000 (inclusive) invoice at 18% has a base of Rs 1,00,000 and GST of Rs 18,000.
Frequently asked questions
Who charges GST to me?
Registered businesses transfer GST to the government on each taxable sale. As a consumer you simply see it on the invoice. Only businesses registered under GST need to collect it.
Is GST included in selling price or added on top?
In retail, GST is usually included in the MRP or displayed price. In business quotations it is often shown separately on top of the base price. The calculator above supports both.
Can I use this for reverse-charge calculations?
Yes. Reverse charge just means the buyer deposits GST instead of the seller. Pick the applicable rate and the amount basis stays the same - the calculator handles it.