GST calculator
Add or remove GST at any slab, split into CGST and SGST for a supply within a state or a single IGST across one.
The value before tax.
A supply within one state carries CGST and SGST; one across states carries IGST.
Leave blank for a supply made today. Fill it in to compute at the rates that applied then.
Invoice total
₹11,800.00
| Taxable value | ₹10,000.00 |
|---|---|
| CGST at 9% | ₹900.00 |
| SGST at 9% | ₹900.00 |
| Total GST | ₹1,800.00 |
| Invoice total | ₹11,800.00 |
| GST rounded to the rupeeSection 170 rounds tax payable to the nearest rupee. | ₹1,800 |
How this worksShow
How GST is worked out
GST is charged on the transaction value of a supply. Adding it is a multiplication; taking it back out of a tax-inclusive price is not, because the tax is a share of the total rather than of the value underneath it. Dividing by 1.18 and dividing by 0.82 are different sums, and the second one is the common mistake.
| Rule | Figure | Statutory basis |
|---|---|---|
| Adding GST to a value | value × rate | s.15, CGST Act 2017 |
| Taking GST out of a price | price × 100 ÷ (100 + rate) | s.15 read with Rule 35, CGST Rules 2017 |
| Within one state | CGST and SGST at half the rate each | s.9, CGST Act 2017 and s.9 of the corresponding State GST Act |
| Between two states | IGST at the whole rate | s.5, IGST Act 2017 |
| Tax payable | rounded to the nearest rupee | s.170, CGST Act 2017 |
Why the date of supply matters
The slabs changed. From 22 September 2025 the live rates are 5% and 18%, with a 40% demerit rate on a narrow list, alongside nil, 3% on bullion and 0.25% on rough diamonds. 12% and 28% are no longer slabs anybody can charge.
They still matter, though, which is why this calculator asks for a date rather than dropping them: a credit note against an older invoice, a revised return or a departmental notice all need the rate that applied to the supply, not the rate that applies now. Leave the date blank and you get today’s slabs.
The paisa nobody notices
Splitting tax into CGST and SGST looks like dividing by two, and on most figures it is. On an odd paisa it is not: tax of ₹1,234.57 halves to ₹617.285, and rounding each component on its own gives two figures of ₹617.29 that add up to ₹1,234.58 — a paisa of tax that exists on neither the invoice nor the return.
- This calculator splits in whole paise and gives the odd one to CGST, so the two components always add back to the tax.
- The tax on a GST-inclusive price is taken as total minus value, never as value times rate, so the three figures always reconcile.
- Section 170 rounding is shown as its own line rather than applied to the working, because the invoice and the return round at different points.
Rates and thresholds as at 10 September 2026. This page is an estimate, not professional advice, and it is not a filing.
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This page works one figure at a time. ComplyADI reads your ledgers, applies the same rules across every transaction, and shows you what is due before the date rather than after it.