How to Calculate GST: Add or Remove GST from Any Price
Simple formulas to add GST to a price, find the GST inside an inclusive price, and split it into CGST and SGST, with worked examples at 5% and 18%.
Goods and services tax, or GST, is added to the price of most things you buy. Shops and freelancers often need to do two opposite calculations: add GST to a price, or find out how much GST is already inside a total. Both take one step once you know the right formula.
Adding GST to a price
GST amount = price × rate ÷ 100 Total price = price × (1 + rate ÷ 100)
A service costs 2,500 before tax, at 18% GST. The GST is 2,500 × 0.18 = 450, and the total is 2,500 × 1.18 = 2,950.
Removing GST from an inclusive price
Price before GST = total ÷ (1 + rate ÷ 100) GST included = total × rate ÷ (100 + rate)
A bill of 2,950 includes 18% GST. The price before tax is 2,950 ÷ 1.18 = 2,500, and the GST inside it is 2,950 × 18 ÷ 118 = 450.
At 5%, an inclusive price of 1,050 is 1,050 ÷ 1.05 = 1,000 before tax, with 50 of GST.
The most common mistake
Taking 18% off the total does not give the price before tax. 18% of 2,950 is 531, which would leave 2,419. That is too low, because the 18% was charged on 2,500, not on 2,950. Always divide by 1 plus the rate.
CGST, SGST and IGST
In India, GST on a sale within one state is split equally between the centre and the state. 18% GST on 2,500 becomes 9% CGST (225) plus 9% SGST (225). For a sale from one state to another, the full 18% (450) is charged as IGST instead.
The same maths works for VAT
Countries with VAT use exactly the same formulas. At the UK's 20% rate, a price of 60 including VAT is 60 ÷ 1.2 = 50 before VAT, so the VAT is 10, which is one sixth of the total.
Tip GST rates differ by product and are revised from time to time. Check the current rate for your item before you invoice.
Try it yourself: GST & VAT CalculatorAdd GST or VAT to a price, or remove it from a price that already includes taxOpen →Common questions
How do I add 18% GST to an amount?
Multiply the amount by 1.18. 1,000 becomes 1,180, of which 180 is GST.
How do I find GST from a total that includes it?
Multiply the total by the rate and divide by 100 plus the rate. For 1,180 at 18%: 1,180 × 18 ÷ 118 = 180.
Is CGST plus SGST the same as IGST?
Yes, in total. Within a state the tax is split into CGST and SGST; between states it is charged as IGST at the full rate.