About this tool

GST Calculator

Calculate inclusive or exclusive GST with CGST, SGST, and IGST breakdowns.

The GST Calculator runs both directions on the same screen. In Add GST mode it multiplies the taxable value by the rate (tax = amount × rate ÷ 100); in Extract GST mode it divides a tax-inclusive figure by (1 + rate ÷ 100) to recover the base, then takes the difference as tax. That tax is halved into CGST and SGST for an intra-state supply, or reported in full as IGST for an inter-state one. All of it is plain JavaScript arithmetic inside a React useMemo hook that re-runs on every keystroke — no submit button, no API call, no upload — with amounts formatted through Intl.NumberFormat in the en-IN locale, so figures render in rupees with Indian lakh and crore digit grouping.

How to use GST Calculator

1. 1

   Open GST Calculator on AltFTool — it loads instantly in your browser.

2. 2

   Type the amount, then tap a rate — 0, 3, 5, 12, 18 or 28% — or load one of the three presets.

3. 3

   Choose Add GST to build a total from a net figure or Extract GST to pull the taxable value out of an inclusive one, then set CGST + SGST for an intra-state supply or IGST for an inter-state supply.

4. 4

   Read the six result cards — taxable value, GST amount, CGST, SGST, IGST and final amount — then copy the report or download it as gst-calculation-report.txt.

Why use GST Calculator

• Both directions, one screen

  Toggle between Add GST and Extract GST without retyping anything — the amount, rate and supply type carry across, and all six figures update as you type.

• Every tax head shown separately

  Taxable value, GST amount, CGST, SGST, IGST and final amount each get their own card, so an intra-state supply reads as two equal halves and an inter-state one as a single IGST line.

• One-tap presets and reset

  Three presets load a complete scenario at once — a ₹10,000 standard invoice at 18%, an ₹11,800 bill to extract, and a ₹50,000 interstate quote — and Reset returns the form to ₹10,000 at 18%, intra-state.

• Free, no account, nothing uploaded

  All six rate slabs and both modes are available without signup, and the arithmetic executes entirely in your browser — the amounts you type never leave the device.

Common use cases

• Pricing an invoice from a net figure — ₹10,000 at 18% shows ₹1,800 GST and an ₹11,800 total, already split into ₹900 CGST and ₹900 SGST.
• Working backwards from an all-in price a customer was quoted, so an ₹11,800 receipt at 18% resolves to ₹10,000 taxable value and ₹1,800 tax.
• Switching a quote to an inter-state supply, where the whole tax sits in IGST instead of being halved across CGST and SGST.

Frequently asked questions