GST Inclusive vs Exclusive: How to Calculate GST Correctly

Learn how to add GST to a base price and extract GST from an inclusive price.

GST calculations are often confusing because an invoice can show either a taxable value before GST or a final price that already includes GST. The mathematical operation is different in each case.

GST-exclusive price

If ₹1,000 is the taxable value and the applicable GST rate is 18%, GST is ₹180 and the final amount is ₹1,180.

GST-inclusive price

If ₹1,180 is already inclusive of 18% GST, the GST component is calculated as 1,180 × 18 ÷ 118 = ₹180. The taxable value is ₹1,000.

Why the denominator changes

An inclusive amount represents 100% of the base plus the GST percentage. At 18%, that total is 118%, so extracting GST uses 18/118 rather than 18/100.

Important

The calculator does not determine which GST rate or classification applies to a product or service. Confirm the applicable tax treatment from current official GST guidance.