Identify the MRP and the applicable GST rate
If MRP is GST-inclusive, use: GST amount = MRP × GST rate ÷ (100 + GST rate)
If MRP is GST-exclusive, use: GST amount = MRP × GST rate ÷ 100
Calculate the base price if needed: Base price = MRP ÷ (1 + GST rate ÷ 100)
Calculate the final price if GST is added separately: Final price = Base price + GST amount
Example for 18% GST on an MRP of 118: GST amount = 118 × 18 ÷ 118 = 18
Example for 18% GST on a pre-tax price of 100: GST amount = 100 × 18 ÷ 100 = 18