How to Calculate GST: Add, Remove and Split (India Guide)

GST math seems simple until you try to extract tax from an inclusive price by hand and get it wrong. Here's how to add, remove and split GST correctly.

Adding GST

GST amount = base price × rate ÷ 100. On ₹1,000 at 18%, GST is ₹180, total ₹1,180. The GST calculator does this and the reverse instantly.

Removing GST (the tricky one)

To find the base inside an inclusive price: base = final price × 100 ÷ (100 + rate). For ₹1,180 inclusive of 18%, base = 1,180 × 100 ÷ 118 = ₹1,000 — NOT ₹1,180 minus 18%. Subtracting the rate from an inclusive price is the most common GST mistake.

The CGST/SGST split

For sales within a state, GST splits into two equal halves: 18% becomes 9% CGST + 9% SGST. Inter-state sales use IGST at the full rate. The calculator shows the split automatically.

Common rates

5% (essentials), 12% (processed foods), 18% (most goods and services — the default), 28% (luxury). Always confirm the current rate for your product category.

For freelancers and shops

State clearly whether your quote is GST-inclusive or exclusive. Pair invoices with the invoice generator and a UPI QR code for easy payment.