GST Reverse Calculator

Taxable value = Inclusive amount ÷ (1 + GST rate ÷ 100)

GST amount = Inclusive amount − Taxable value

For intra-state supplies the GST amount is split into equal CGST and SGST halves. For inter-state supplies the whole amount is IGST.

A customer paid ₹11,800 including 18% GST. Taxable value = 11,800 ÷ 1.18 = ₹10,000, so GST = ₹1,800 — CGST ₹900 and SGST ₹900 within the same state.

Retail India runs on round numbers. A customer pays ₹500 for a haircut, ₹2,000 for a repair or scans a UPI QR for the exact bill total, and nobody writes the tax separately at the counter. Your books, however, need the split: the taxable value feeds turnover and the tax component feeds your output liability. Reverse calculation is the bridge between what the customer paid and what the return expects.

The extraction formula divides rather than subtracts. Dividing the inclusive amount by one plus the rate as a decimal isolates the base; the remainder is tax. At 18% this means the tax is roughly 15.25% of the inclusive figure, not 18% of it — a gap that grows with the slab and quietly distorts a full month of collections if you subtract instead of divide.

This also matters for reconciliation. Payment gateways, marketplaces and card settlements report gross inclusive amounts net of their own commission, so you need the inclusive-to-taxable step before you can match settlement reports with your sales register or explain a GSTR-1 versus GSTR-3B difference to your accountant.