GST amount = Original price × GST rate
GST-inclusive price = Original price + GST amount
GST-exclusive price = GST-inclusive price ÷ (1 + GST rate)
GST percentage = (GST amount ÷ Original price) × 100
If GST-inclusive price and GST-exclusive price are known, GST amount = GST-inclusive price − GST-exclusive price
If GST-inclusive price is known, GST rate = [(GST-inclusive price ÷ GST-exclusive price) − 1] × 100
If GST amount and original price are known, GST percentage = (GST amount ÷ Original price) × 100
Convert the GST rate to a decimal before calculating
Multiply the original price by the decimal GST rate to get the GST amount
Add the GST amount to the original price to get the total price