A GSTIN looks like a longer, scarier version of a PAN, but it's actually more transparent — every part of its 15 characters has a defined meaning, and unlike a PAN, its final check digit follows a publicly documented formula that can actually be verified.
The five parts
A GSTIN breaks down as: 2-digit state code + 10-character PAN + 1 entity code + a literal "Z" + 1 check digit.
- State code — the first two digits identify the state or union territory the registration is under (e.g. 27 is Maharashtra, 29 is Karnataka, 07 is Delhi). A business registered in multiple states holds a separate GSTIN per state, each sharing the same embedded PAN but a different state code.
- PAN — characters 3 through 12 are the exact 10-character PAN of the business or individual the GSTIN belongs to, embedded directly. This is why a GSTIN reveals the entity's PAN outright, unlike most other identifiers.
- Entity code — the 13th character indicates the registration number for that PAN within that state, for businesses with multiple GST registrations under the same PAN and state.
- "Z" — the 14th character is always the literal letter Z, reserved for future use. If it's anything else, the GSTIN isn't validly formatted.
- Check digit — the 15th and final character, calculated from the first 14 using a defined algorithm.
The check digit actually is verifiable
Unlike PAN's undocumented 10th-character algorithm, GSTN has published the GSTIN check-digit formula: a base-36 Luhn-like checksum computed over the first 14 characters, with alternating weights and a final modulo-36 step. That means, unlike a PAN, you can mathematically confirm whether a GSTIN's final character is internally consistent with the rest of it — genuinely useful as a first-pass sanity check on an invoice or vendor form before it goes further.
Worth being precise about what that check actually proves, though: a matching check digit confirms the GSTIN is internally well-formed — the 15 characters are mathematically consistent with each other. It doesn't confirm the GSTIN was actually issued to a real, currently-registered business; that still requires checking the government's GST portal directly, the same limitation format validation always has.
Using the tool
Our GSTIN Validator parses all five parts, names the state from the embedded code, extracts the embedded PAN, and calculates the check digit to confirm it's internally consistent — flagging a mismatch as "unconfirmed" rather than an outright rejection, since a live portal lookup is the only way to fully confirm a GSTIN is genuinely registered.
Try it here: GSTIN Validator.