Goods and Services Tax (GST) is India's unified indirect tax system that replaced multiple taxes like VAT, service tax, and excise duty. Whether you're a small business owner, freelancer, CA, or e-commerce seller, understanding GST calculations is essential for accurate invoicing and compliance.
In this complete guide, we'll walk you through how GST works in India, the current GST rates, the difference between CGST/SGST/IGST, and how to calculate GST on any amount — with real examples using ₹ amounts.
What Is GST and How Does It Work in India?
GST (Goods and Services Tax) is a comprehensive indirect tax levied on the manufacture, sale, and consumption of goods and services across India. Introduced on July 1, 2017, GST replaced over 15 indirect taxes including VAT, service tax, excise duty, and octroi.
The GST system operates on a dual model:
- CGST (Central GST) — Collected by the Central Government
- SGST (State GST) — Collected by the State Government
- IGST (Integrated GST) — Collected on inter-state transactions
Current GST Rates in India (2026)
India has four main GST slabs, plus a special 0.25% and 3% rate for specific items:
| GST Rate | Category | Examples |
|---|---|---|
| 0% | Essential goods | Fresh fruits, vegetables, milk, eggs, bread, salt |
| 5% | Basic necessities | Sugar, tea, coffee, edible oils, coal, fertilizers |
| 12% | Standard goods | Processed food, mobiles, sewing machines, umbrella |
| 18% | Most goods & services | Soap, toothpaste, software, restaurant food, IT services |
| 28% | Luxury & sin goods | Cars, tobacco, AC, washing machine, aerated drinks |
How to Calculate GST: Step-by-Step
Method 1: Adding GST to Base Price
When you know the price before tax and need to find the total price including GST:
Formula: GST Amount = Base Price × GST Rate / 100
Total Price = Base Price + GST Amount
Example: A laptop costs ₹50,000 (before GST) with 18% GST rate.
- GST Amount = ₹50,000 × 18/100 = ₹9,000
- Total Price = ₹50,000 + ₹9,000 = ₹59,000
- If intra-state: CGST = ₹4,500 (9%) + SGST = ₹4,500 (9%)
- If inter-state: IGST = ₹9,000 (18%)
Method 2: Removing GST from Inclusive Price
When you have the final price (GST inclusive) and need to find the base price:
Formula: Base Price = Inclusive Price × 100 / (100 + GST Rate)
Example: A bill shows ₹1,180 (inclusive of 18% GST).
- Base Price = ₹1,180 × 100/118 = ₹1,000
- GST Amount = ₹1,180 - ₹1,000 = ₹180
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This is where many people get confused. The split depends on whether the transaction is within the same state or across states:
| Transaction Type | Tax Applied | Example (18% GST) |
|---|---|---|
| Intra-State (within same state) | CGST + SGST | 9% CGST + 9% SGST = 18% |
| Inter-State (between states) | IGST | 18% IGST |
Example: A Delhi-based company sells goods worth ₹10,000 at 18% GST:
- To a Delhi buyer (intra-state): CGST ₹900 + SGST ₹900 = Total ₹11,800
- To a Mumbai buyer (inter-state): IGST ₹1,800 = Total ₹11,800
The total tax is the same — only the split between central and state differs.
GST Calculation for Common Scenarios
Restaurant Bills
Most restaurants charge 5% GST (without input tax credit). AC restaurants in hotels with room tariff above ₹7,500 charge 18% GST.
Example: Food bill of ₹2,000 at a regular restaurant: GST = ₹2,000 × 5% = ₹100. Total = ₹2,100.
Freelancer/Consultant Services
Professional services attract 18% GST. If you're a freelancer earning above ₹20 lakh annually (₹10 lakh for special category states), you must register for GST.
E-commerce Sellers
Amazon/Flipkart sellers must charge GST on every product based on its HSN code. The marketplace collects TCS (Tax Collected at Source) at 1%.
Frequently Asked Questions
Who needs to register for GST in India?
Businesses with annual turnover above ₹20 lakh (₹10 lakh for NE states and special category states) must register for GST. E-commerce sellers must register regardless of turnover.
How do I calculate GST on ₹1,000 at 18%?
GST = ₹1,000 × 18/100 = ₹180. Total = ₹1,180. For intra-state: CGST = ₹90, SGST = ₹90. For inter-state: IGST = ₹180.
What is the difference between CGST and SGST?
Both are components of GST on intra-state transactions. CGST goes to the Central Government and SGST goes to the State Government. Each is half the total GST rate.
Can I use a GST calculator for filing returns?
GST calculators help you verify amounts for invoices and returns. However, official GST return filing must be done on the GST portal (gst.gov.in) using your GSTIN.
What is reverse charge mechanism in GST?
Under reverse charge (RCM), the buyer pays GST instead of the seller. This applies to specific goods/services like legal services, transportation by GTA, and purchases from unregistered dealers above ₹5,000/day.