GST inclusive vs exclusive: a worked invoice example

From an exclusive price

If the taxable value is ₹1,000 and the rate is 18%, the GST is ₹180 and the invoice total is ₹1,180. For an intra-state sale, CGST is ₹90 and SGST is ₹90. The taxable value never changes because tax was added after it was set.

Taxable value: ₹1,000.00
CGST 9%:       ₹90.00
SGST 9%:       ₹90.00
Invoice total: ₹1,180.00

From an inclusive price

If the customer pays ₹1,180 including 18% GST, the taxable value is 1,180 ÷ 1.18 = ₹1,000. The tax is ₹180. Extracting tax uses division, not subtraction of 18% of the gross amount — 18% of ₹1,180 is ₹212.40, which is the common error.

Gross amount:  ₹1,180.00
Taxable value: ₹1,000.00  (1,180 ÷ 1.18)
GST total:     ₹180.00
CGST / SGST:   ₹90.00 each

Rates and rounding

Common GST slabs in India are 5%, 12%, 18% and 28%, with special rates for some goods and services. The rate that applies depends on the classification of what you supply, not on what is convenient for the invoice.

Round at the invoice level according to your accounting policy, and keep the taxable value and tax lines internally consistent. A calculator result is a check, not a substitute for professional tax advice.

A quick sanity check

Tax should always be less than the gross for inclusive prices, and the taxable value should be less than or equal to the gross. If your calculated tax exceeds the difference between gross and net, you have applied the rate in the wrong direction.