1. Add GST to a price
GST = P × R ÷ 100 · Total = P × (1 + R ÷ 100)
P = ₹750, R = 5% → GST ₹37.50, Total ₹787.50.
2. Remove GST from an inclusive price
P = T ÷ (1 + R ÷ 100) · GST = T − P
T = ₹4,720, R = 18% → P = ₹4,000, GST = ₹720.
3. GST share of an inclusive price
GST = T × R ÷ (100 + R)
At 18% the GST is 18/118 = 15.254% of the total; at 5% it is 5/105 = 4.762%; at 40% it is 40/140 = 28.571%.
4. CGST, SGST and IGST
CGST = SGST/UTGST = P × (R ÷ 2) ÷ 100 · IGST = P × R ÷ 100
P = ₹12,345, R = 18% → CGST ₹1,111.05, SGST ₹1,111.05 (total ₹2,222.10); IGST would be ₹2,222.10.
5. Discount then GST
Taxable = P × Q × (1 − D ÷ 100) · Total = Taxable × (1 + R ÷ 100)
P = ₹2,000, Q = 2, D = 10%, R = 18% → taxable ₹3,600, GST ₹648, total ₹4,248.
6. Multi-item totals
Total GST = Σ (taxable value of each line × its rate ÷ 100)
Compute and round tax per line (or per rate group), then add — never apply one rate to a mixed bill.
Rounding rule used here
Amounts are kept exact in decimal arithmetic and each tax amount is rounded to the nearest paisa, with half a paisa rounded up. No binary floating-point is used, so ₹0.10 × 3 is exactly ₹0.30.
Ready to try? Open the GST calculator.
Last reviewed 29 October 2026.