Goods and Services Tax (GST) is a destination-based tax on consumption of goods and services. Whether you are a business owner generating invoices or a consumer checking a bill, understanding how to calculate GST correctly is essential.
1. Adding GST (Forward Calculation)
This is the most common scenario. You have a base price (exclusive of tax) and you need to add the tax amount to find the final price.
Total Price = Base Price + GST Amount
Example: A product costs 1,000 and the GST rate is 18%.
- GST = (1000 × 18) / 100 = 180
- Total = 1000 + 180 = 1,180
2. Removing GST (Reverse Calculation)
This is useful when you have a total bill amount (inclusive of tax) and want to find out the original base price before tax was added.
Example: You paid 1,180 for an item that includes 18% GST.
- Base Price = 1180 / (1 + 0.18)
- Base Price = 1180 / 1.18 = 1,000
Confused by the Math?
Use our free tool to instantly add or remove GST from any amount.
Open GST CalculatorCurrent GST Rate Slabs (2025)
While rates vary by country (and product), these are the standard slabs used in many regions like India:
| Rate | Item Category |
|---|---|
| 0% | Essential foods (Milk, Bread, Salt) |
| 5% | Economy class air travel, Packaged food |
| 12% | Processed foods, Mobiles, Computers |
| 18% | Standard services, Capital goods (Most common) |
| 28% | Luxury items, Automobiles, 5-star hotels |
Common Mistakes to Avoid
The biggest mistake people make is calculating reverse GST by simply subtracting the percentage.
Example: If total is 100 with 10% tax, the base is NOT 90 (100 - 10%). It is actually 90.90 (100 / 1.1).