How is a GSTIN structured?

15 characters — a 2-digit state code, the entity's 10-character PAN, a 1-character entity number, the reserved letter Z, and a base-36 check digit computed over the first 14 characters.

What is the PAN inside a GSTIN?

Characters 3 to 12 of the GSTIN are the holder's 10-character PAN (Permanent Account Number), in the pattern of five letters, four digits and one letter — for example AAAAA0000A.

What does the state code at the start mean?

The first two digits are the GST state code identifying the place of registration — for example 27 is Maharashtra, 29 is Karnataka, 22 is Chhattisgarh. The validator decodes it to the state name.

How is the GSTIN check digit calculated?

It is a base-36 check over the first 14 characters. Each character maps to 0-35 (0-9 then A-Z), is multiplied by an alternating factor of 1 and 2, and the quotient plus remainder of dividing each product by 36 are summed. The check value is (36 − sum mod 36) mod 36, mapped back to a character.

Why is the 14th character always Z?

The 14th character is currently reserved and set to the letter Z by default in the GSTIN scheme. The 13th character is the entity (registration) number for that PAN within the state.

Does a valid GSTIN mean the business is registered and active?

No. A pass confirms the number is well-formed — correct length, valid state code, valid PAN pattern, and matching check digit. Only a lookup on the official GST portal confirms an active registration.

Is my GSTIN sent anywhere?

No. The check digit is computed entirely in your browser — privacy-first, the GSTIN never leaves your device and no GST portal lookup is made.

India GSTIN Validator

This tool validates the format of a 15-character India GSTIN (GST Identification Number). It decodes the state code, checks the embedded PAN, and recomputes the check digit offline — useful for catching typos on invoices and in vendor records before filing.

How it works

A GSTIN is 15 characters with a fixed structure:

Position	Length	Meaning
1–2	2	State code (e.g. 27 = Maharashtra)
3–12	10	Holder’s PAN (AAAAA0000A pattern)
13	1	Entity number for that PAN in the state
14	1	Reserved (currently Z)
15	1	Base-36 check digit

The validator decodes the state code to a name, verifies the embedded PAN pattern (five letters, four digits, one letter), and recomputes the GSTN base-36 check digit over the first 14 characters: each character maps to 0–35 (0–9 then A–Z), is multiplied by an alternating factor of 1 and 2, and the quotient and remainder of dividing each product by 36 are summed; the check value is (36 − sum mod 36) mod 36. It compares that to the 15th character.

Example

For 22AAAAA0000A1Z5:

State code 22 → Chhattisgarh
PAN = AAAAA0000A → matches the valid pattern
Entity number 1, reserved Z
Check digit recomputed over the first 14 characters and compared to 5

If the recomputed digit matches, the GSTIN is well-formed.

This is privacy-first: the check digit is computed locally with no GST portal lookup. A valid result means the number is well-formed — verify an active registration on the official GST portal.