The Complete Indian GST Calculation Guide: CGST, SGST & IGST Explained

## Understanding Goods and Services Tax (GST) The Goods and Services Tax (GST) is an indirect comprehensive tax levied on the manufacture, sale, and consumption of goods and services throughout India. For small business owners, freelancers, and online sellers, understanding how to calculate GST both forwards (exclusive) and backwards (inclusive) is essential for compliant invoicing. ### Intra-State vs. Inter-State Transactions 1. **Intra-State Transactions (Within the Same State)**: - When buyer and supplier are located in the same state. - Tax is equally divided into **CGST** (Central GST, 50%) and **SGST** (State GST, 50%). - Example: On an 18% slab, 9% is CGST and 9% is SGST. 2. **Inter-State Transactions (Between Two Different States)**: - When goods or services are supplied across state borders. - Entire tax is levied as **IGST** (Integrated GST, 100%) and collected by the Central Government. ### The Essential Mathematical Formulas #### 1. GST Exclusive (Adding GST to Base Price) When you have the cost of a product and need to add GST: $\text{GST Amount} = \frac{\text{Base Price} \times \text{GST Rate}}{100}$ $\text{Total Invoice Amount} = \text{Base Price} + \text{GST Amount}$ #### 2. GST Inclusive (Extracting GST from Gross Price) When a price is quoted inclusive of all taxes (e.g., retail price of ₹1,180 with 18% GST): $\text{Base Price} = \frac{\text{Total Amount} \times 100}{100 + \text{GST Rate}}$ $\text{GST Amount} = \text{Total Amount} - \text{Base Price}$ For ₹1,180 at 18%: - Base Price = ₹1,180 × 100 / 118 = ₹1,000 - Total GST = ₹180 (Split into ₹90 CGST + ₹90 SGST) Use the **SmartAI GST / VAT Calculator** for instant error-free tax computations with itemized invoice summaries.