How this calculation works
Adding GST applies the entered percentage to the taxable amount. Removing GST reverses that multiplication. An inclusive GST amount is not found by subtracting the rate percentage from the total.
Exclusive: total = base × (1 + rate/100); inclusive: base = total ÷ (1 + rate/100)A worked example
₹1,000 before GST at an entered 18% rate becomes ₹1,180, including ₹180 GST.
Good to know
Uses your entered rate only. It does not classify goods or services, determine an applicable rate, or model cess, input-tax credits or place-of-supply rules.
Why removing 18% GST does not mean subtracting 18%
An inclusive price is already 118% of its base when the entered rate is 18%. For a total of ₹1,180, the base is ₹1,180 ÷ 1.18 = ₹1,000. The tax is ₹180, which is about 15.25% of the inclusive total, even though it is 18% of the base.
This is a question about the denominator. Subtracting 18% of ₹1,180 would remove ₹212.40 and produce the wrong taxable value. Reversing a percentage increase requires division by its growth factor.
Use the correct rate before trusting the arithmetic
The rate field is an input, not a classification decision. Whether a supply attracts a particular rate, an exemption, cess or special treatment depends on the applicable rules. The calculator cannot determine those facts from an amount alone.
For invoice work, check the rate, tax basis and required rounding with the relevant official guidance or accounting process. This tool shows a total GST amount; it does not allocate tax between CGST, SGST and IGST or assess input-tax-credit eligibility.
A few questions, answered
Does this find the legally applicable GST rate?
No. You must enter the correct rate for the transaction.
Is the entered amount before or after GST?
Choose Add GST for an exclusive amount, or Remove included GST for an inclusive amount.