GST Number (GSTIN) Validator
This GSTIN validator checks whether a GST number is genuinely well-formed. It verifies the 15-character structure, looks up the state code, checks the embedded PAN pattern, and — unlike simple format checkers — computes the real mod-36 check digit to confirm the final character is correct. Paste a GSTIN and see exactly what passes or fails.
Typing auto-converts to uppercase. Validation runs as you type.
What the validator checks
- Length & pattern — exactly 15 characters in the correct arrangement.
- State code (1st–2nd) — matched against the official GST state code list, with the state name shown.
- PAN (3rd–12th) — the 10-character block must follow the PAN pattern (AAAAA9999A).
- Entity code (13th) — indicates the number of registrations for that PAN in the state.
- Default letter (14th) — normally the letter "Z".
- Checksum (15th) — recomputed with the mod-36 algorithm and compared to the entered character.
How the GSTIN checksum works
Each of the first 14 characters is converted to a value (0–9 for digits, 10–35 for A–Z). Working right to left, values are multiplied by an alternating factor of 1 and 2; each product is reduced by adding its quotient and remainder when divided by 36. The check character is (36 − (sum mod 36)) mod 36, mapped back to a digit or letter. If it does not match the 15th character, the GSTIN is invalid.
FAQ
How is a GSTIN validated?
A valid GSTIN is 15 characters: a 2-digit state code, a 10-character PAN, a 13th entity digit, the letter Z, and a final mod-36 check character. This tool checks all of these.
Does a valid checksum mean the business is registered?
No. It only confirms the number is well-formed. To confirm active registration, verify on the official GST portal.
Why did my GSTIN fail?
The tool lists the exact reason — wrong length, invalid state code, bad PAN pattern, or a mismatched checksum digit.
Related tools
PAN Validator
Check a PAN and its entity type.
State Codes
Full GST state code list.
GST Bill Generator
Live GSTIN check while billing.
Guide: GSTIN format
What each digit means.
GST Calculator
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HSN Finder
Find HSN codes and rates.
Last updated: 2 July 2026.