FinCalculator
Business & SME APIWeb Calculator UI

Free GST Invoice Totals API (CGST, SGST, IGST) (2026)

For invoicing tools and freelancer platforms. The discount comes off before tax (CGST rule 46(k)); a same-state supply splits the rate into CGST and SGST, each rounded to the paisa on its own; another state is IGST; an export under LUT is IGST 0%. GET takes one amount; POST a JSON body `{ items: [{ quantity, unitPrice }], discount, gstRate, supply, currency }` for line items.

Interactive API Playground & Live Test

GET/api/v1/invoice

Query Parameters

Invoice value before discount and tax

'intra' (client in your state), 'inter' (another state), 'export' or 'none' (not registered for GST); default intra

GST rate in % (default 18)

Discount in %, taken off before tax (default 0)

Export only: true to charge IGST instead of exporting under LUT (default false)

3-letter ISO code for the amount in words (default INR)

curl -X GET "https://fincalculator.in/api/v1/invoice?amount=80000&supply=intra&gstRate=18&discount=0&exportWithIgst=false&currency=INR" \
  -H "Accept: application/json"
Live JSON Response (HTTP 200 OK)
Click "Execute Live API Request" below...

Request Parameters Schema

ParameterTypeRequiredDescription / Notes
amountnumberRequiredInvoice value before discount and tax
supplystringOptional'intra' (client in your state), 'inter' (another state), 'export' or 'none' (not registered for GST); default intra
gstRatenumberOptionalGST rate in % (default 18)
discountnumberOptionalDiscount in %, taken off before tax (default 0)
exportWithIgstbooleanOptionalExport only: true to charge IGST instead of exporting under LUT (default false)
currencystringOptional3-letter ISO code for the amount in words (default INR)

Related Business & SME APIs

GET /api/v1/gst-itcFree GST Input Tax Credit (ITC) Calculator APIGET /api/v1/edf-deadlineFree EDF (Export Declaration Form) Deadline APIGET /api/v1/startup-burn-rateFree Startup Burn Rate & Cash Runway APIGET /api/v1/rental-yieldFree Rental Yield & Property Income API

Frequently Asked Questions (FAQs)

Is the Free GST Invoice Totals API (CGST, SGST, IGST) free to use in production apps?
Yes! All FinCalculator REST APIs are completely free, zero-auth, open-CORS, and edge-cached for high performance across global web and mobile applications.
What is the rate limit for /api/v1/invoice?
Endpoints are cached at the edge for 24 hours. There are no restrictive rate limits for standard web traffic and mobile applications.