GST Calculator Guide: How to Calculate GST, Slabs & Input Credit Explained
Whether you're a business owner pricing a product, a freelancer raising an invoice, or just checking if a shopkeeper charged you correctly — understanding GST calculation is a practical everyday skill in India.
This guide covers GST slabs, the exact formulas to add or remove GST from a price, and the basics of CGST/SGST/IGST.
Current GST Slabs in India
| GST Rate | Applies To |
|---|---|
| 0% | Fresh fruits, vegetables, milk, educational services, books |
| 5% | Packaged food items, footwear under ₹1,000, life-saving drugs |
| 12% | Processed food, mobile phones, business class air tickets |
| 18% | Most goods and services — electronics, IT services, restaurants (non-AC in some cases) |
| 28% | Luxury and sin goods — cars, tobacco, aerated drinks |
Note: GST rates are revised periodically by the GST Council. Always verify the current rate for your specific product/service category before finalizing invoices.
How to Add GST to a Price
GST Amount = Original Price × (GST Rate ÷ 100)
Final Price = Original Price + GST Amount
Example
Product price (before GST): ₹1,000 | GST rate: 18%
- GST amount = 1,000 × 0.18 = ₹180
- Final price = 1,000 + 180 = ₹1,180
How to Remove GST from a Price (Reverse Calculation)
This is trickier — useful when you have the final MRP and want to know the base price and GST portion.
Original Price = Final Price ÷ (1 + GST Rate/100)
GST Amount = Final Price − Original Price
Example
Final price (GST-inclusive): ₹1,180 | GST rate: 18%
- Original price = 1,180 ÷ 1.18 = ₹1,000
- GST amount = 1,180 − 1,000 = ₹180
Common mistake: People often calculate 18% of ₹1,180 (= ₹212.40) thinking that's the GST — this is wrong. GST was charged on the original ₹1,000, not the final price. Always divide, don't just multiply, when reverse-calculating.
CGST vs SGST vs IGST: What's the Difference?
| Type | When Applied | Goes To |
|---|---|---|
| CGST (Central GST) | Intra-state sale (within same state) | Central Government |
| SGST (State GST) | Intra-state sale (within same state) | State Government |
| IGST (Integrated GST) | Inter-state sale (between two states) | Split between Centre & destination State |
Key rule: For intra-state sales, GST is split equally: e.g., 18% GST = 9% CGST + 9% SGST. For inter-state sales, the full 18% is charged as IGST.
Example: Intra-State Sale (Within Maharashtra)
- Sale value: ₹10,000 | GST rate: 18%
- CGST (9%): ₹900
- SGST (9%): ₹900
- Total GST: ₹1,800 | Invoice total: ₹11,800
Example: Inter-State Sale (Maharashtra to Karnataka)
- Sale value: ₹10,000 | GST rate: 18%
- IGST (18%): ₹1,800
- Invoice total: ₹11,800 (same total, different split)
Input Tax Credit (ITC): The Basics
If you're a GST-registered business, you can claim credit for GST you've already paid on business purchases (inputs), and offset it against the GST you collect on sales (output).
Simple example: You buy raw material for ₹1,00,000 + 18% GST = ₹18,000 GST paid. You sell finished goods for ₹2,00,000 + 18% GST = ₹36,000 GST collected. Your net GST liability to pay = ₹36,000 − ₹18,000 = ₹18,000 (not the full ₹36,000).
This prevents "tax on tax" and is one of GST's core design principles — it's why businesses must keep proper purchase invoices to claim ITC.
Frequently Asked Questions
Need to calculate GST instantly for any amount and slab? Use our free GST Calculator →
Related Calculators
- Income Tax Calculator — for personal tax liability
- Discount Calculator — combine discounts with GST pricing
- Profit Margin Calculator — price your products correctly after tax