How the GST calculation works
Adding GST (when your price is exclusive of tax): GST = base × rate ÷ 100, and the total is base + GST. Removing GST (when your price already includes tax): base = amount ÷ (1 + rate ÷ 100), and the GST is the difference.
For an intra-state supply the GST is split equally into CGST and SGST; for an inter-state supply the whole amount is IGST. The total tax is the same either way — only the split changes.
When you are ready to turn these numbers into compliant documents, our GST billing software applies the right tax automatically, and our guide to the GST invoice format shows exactly what each invoice must contain.
FAQs
How do I add GST to an amount?
Multiply the base amount by the GST rate. For example, ₹1,000 at 18% GST is ₹180 GST, giving a total of ₹1,180. This calculator does it instantly and also splits the tax into CGST and SGST, or IGST.
How do I remove GST from an inclusive price?
Divide the GST-inclusive amount by (1 + rate/100). For ₹1,180 at 18%, the base is ₹1,180 ÷ 1.18 = ₹1,000, so the GST portion is ₹180. Use the "Remove GST" mode for this.
What is the difference between CGST, SGST and IGST?
For a sale within the same state (intra-state), GST is split equally into CGST and SGST. For a sale between states (inter-state), the whole amount is IGST. The rate total is the same either way.
Which GST rate should I use?
Common GST slabs are 0%, 5%, 12%, 18% and 28%, with 3% for items such as gold. The correct rate depends on the specific goods or service — check the rate that applies to you or ask your CA.
Is this GST calculator free?
Yes, it is completely free with no sign-up. For turning these figures into compliant GST invoices and books, Vastuguruji Books has a free plan too.