What is GST Calculator?
Work out GST in both directions: add GST to a base price, or strip it out of a total that already includes it. The CGST and SGST split is shown automatically, which is what you need when preparing an invoice or checking a bill.
How to use GST Calculator
- Choose “Add GST” if your amount is before tax, or “Remove GST” if the amount already includes it.
- Enter the amount.
- Select the applicable GST rate — 3%, 5%, 12%, 18% or 28%.
- Read off the base amount, GST, the CGST + SGST split and the final total.
Why use this tool?
Works both ways
Reverse GST calculation is the part people get wrong most often — you cannot simply subtract 18% from an inclusive price. This handles the correct formula for you.
CGST and SGST split included
Intra-state invoices must show the tax halved into CGST and SGST. That breakup is calculated automatically.
Frequently asked questions
How do I remove GST from an inclusive amount?
Divide by (1 + rate/100) — so for 18% GST you divide the total by 1.18 to get the base. Subtracting 18% is a common mistake and gives the wrong answer; this calculator uses the correct formula.
What is the difference between CGST, SGST and IGST?
For sales within a state, GST is split equally into CGST (central) and SGST (state). For sales between states, the same total is charged as a single IGST instead.
Is this tool really free?
Yes, completely free with no limits, no watermarks, no account and no trial period. Because everything runs on your own device, there are no server costs to pass on to you.