Reverse GST Calculator - Extract Base Price from GST-Inclusive Amount

Reverse GST calculation is the process of extracting the base amount (before GST) and GST amount from a tax-inclusive price. The formula is: Base Amount = Inclusive Amount × 100 ÷ (100 + GST Rate). For example, if an item costs ₹1,180 inclusive of 18% GST, the base amount is ₹1,000 and GST is ₹180.

To calculate GST from an inclusive price: First find the base amount using Base = Inclusive × 100 ÷ (100 + Rate). Then GST Amount = Inclusive Amount - Base Amount. For 18% GST on ₹1,180: Base = 1180 × 100 ÷ 118 = ₹1,000, GST = 1180 - 1000 = ₹180.

The reverse GST calculation formula is: Base Amount = (Inclusive Amount × 100) ÷ (100 + GST Rate). GST Amount = Inclusive Amount - Base Amount. For CGST/SGST split (intra-state): Each = GST Amount ÷ 2. For IGST (inter-state): IGST = Full GST Amount.

Reverse GST calculation is needed when: 1) You receive an invoice showing only the total amount without GST breakdown, 2) You need to claim Input Tax Credit and must know the exact GST paid, 3) You're preparing accounts and need to separate base value from GST, 4) You're verifying invoice calculations from suppliers.

For Intra-State transactions (within same state), GST is split equally into CGST (Central GST) and SGST (State GST). For Inter-State transactions (between different states), the entire GST is collected as IGST (Integrated GST). The total GST amount remains the same; only the split differs. Use CGST+SGST for local transactions and IGST for interstate sales.