How GST Calculation Works
The Goods and Services Tax (GST) is a destination-based, multi-stage indirect tax implemented in India in July 2017 to replace numerous cascading taxes (VAT, Excise Duty, Service Tax, Octroi).
When generating an invoice or purchasing goods, GST can be applied in two directions:
- Exclusive GST (Add Tax): Starting with a net wholesale or base manufacturing cost and adding statutory tax to calculate the customer billing amount.
- Inclusive GST (Extract Tax): Starting with a maximum retail price (MRP) or final gross bill and removing the built-in tax to reveal the true underlying merchant cost.
• GST Amount = (Base Amount × GST Rate) ÷ 100
• Gross Total = Base Amount + GST Amount
Removing GST (Inclusive):
• Base Amount = (Gross Total × 100) ÷ (100 + GST Rate)
• GST Amount = Gross Total − Base Amount Intra-State Split: CGST = GST ÷ 2 | SGST = GST ÷ 2
Inter-State Transaction: IGST = Full GST Amount
Worked Example: Adding & Removing 18% GST
Case A: Adding 18% GST to ₹1,000 (Exclusive)
- Base price = ₹1,000
- GST = $\frac{1000 \times 18}{100} =$ ₹180
- Total invoice value = ₹1,000 + ₹180 = ₹1,180
- Tax breakdown: CGST (9%) = ₹90, SGST (9%) = ₹90
Case B: Extracting 18% GST from ₹1,180 (Inclusive MRP)
- Gross total = ₹1,180
- Base price = $\frac{1,180 \times 100}{100 + 18} = \frac{118000}{118} =$ ₹1,000
- Embedded GST = ₹1,180 - ₹1,000 = ₹180
Standard Indian GST Tax Slabs
| Tax Slab | Applicable Goods & Services | CGST + SGST Split |
|---|---|---|
| 0% (Nil Rate) | Unbranded grains, fresh milk, vegetables, eggs, curd, salt, legal services. | 0% + 0% |
| 5% Slab | Packaged foods, tea, coffee, edible oil, economy domestic air travel, life-saving medicines. | 2.5% + 2.5% |
| 12% Slab | Butter, cheese, processed fruit juices, mobile phones, business class flights. | 6% + 6% |
| 18% Slab | IT software services, consumer electronics, hair oil, banking services, restaurants. | 9% + 9% |
| 28% Slab | Automobiles, luxury motorcycles, air conditioners, cement, gaming, pan masala. | 14% + 14% |
Frequently Asked Questions
To add GST: GST Amount = (Base Price × GST Rate) / 100. Total Price = Base Price + GST Amount. To remove GST from an inclusive price: Base Price = (Gross Price × 100) / (100 + GST Rate).
The primary GST tax slabs in India are 0% (essential food and grains), 5% (basic necessities and economy travel), 12% (processed foods and business class air travel), 18% (standard services and electronic goods), and 28% (luxury items and demerit goods).
For intra-state transactions (within the same state), GST is split equally into Central GST (CGST) and State GST (SGST). For inter-state transactions (between two different states), Integrated GST (IGST) is collected by the Central Government.
⚠️ Tax Disclaimer
This GST calculator is provided for computational assistance. Tax rates and HSN/SAC codes are subject to amendments by the GST Council. Always verify with official GST portal documentation or your chartered accountant.