Does a valid check digit mean the GSTIN is real?

No. The check digit proves the number is internally consistent, which catches typos and invented numbers. It cannot tell you whether the registration exists, is active, or belongs to the business named on the invoice. Only a search on the official GST portal can confirm that.

What do the fifteen characters mean?

The first two digits are the state or union territory code. The next ten characters are the PAN of the registered person. The thirteenth is the entity number for that PAN within that state, so a second registration in the same state gets a 2. The fourteenth is Z, currently unused. The fifteenth is a checksum computed from the first fourteen.

Why does my supplier have several GSTINs?

Registration is state-wise. A business operating in four states holds four GSTINs, all built on the same PAN. The one that belongs on your invoice is the one for the state that made the supply.

How is the check digit calculated?

Each of the first fourteen characters is converted to a value from 0 to 35, multiplied by an alternating factor of 1 or 2 working from the right, and the quotient and remainder of that product divided by 36 are added together. The check character is whatever value brings the running total up to the next multiple of 36.

GSTIN validator

Paste a 15-character GSTIN. This checks the pattern, the state code and the checksum, and shows you the PAN inside it. It catches typos, not fraud.

GSTIN

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Enter a GSTIN above.

What this checks, and what it cannot

A GSTIN carries its own error detection. The last character is derived arithmetically from the other fourteen, so changing any single character almost always breaks the checksum. That makes this an excellent typo catcher: a number mistyped from a paper invoice will nearly always fail here.

It is not a fraud check. A determined person can construct a well-formed GSTIN that has never been issued to anyone. Structure and existence are different questions. For existence, use the search on the official GST portal, which will also tell you the legal name, the registration date and whether the registration is active or cancelled.

That last part matters more than most people realise. Input tax credit depends on your supplier actually reporting the supply, and a supplier whose registration was cancelled midway through the year is a credit problem waiting to surface at reconciliation. If a supplier is new to you and the invoice is large, check the portal, not just the checksum.

Reading the number

Position	Characters	Meaning
1-2	27	State or union territory code. 27 is Maharashtra, 09 is Uttar Pradesh, 29 is Karnataka.
3-12	AAPFU0939F	PAN of the registered person. The fourth character tells you the entity type: P for individual, C for company, F for firm or LLP, H for HUF, T for trust.
13	1	Entity number for this PAN within this state. A second registration in the same state becomes 2.
14	Z	Fixed. Reserved for future use.
15	V	Checksum computed from the previous fourteen characters.

Common questions

Does a valid check digit mean the GSTIN is real?: No. The check digit proves the number is internally consistent, which catches typos and invented numbers. It cannot tell you whether the registration exists, is active, or belongs to the business named on the invoice. Only a search on the official GST portal can confirm that.
What do the fifteen characters mean?: The first two digits are the state or union territory code. The next ten characters are the PAN of the registered person. The thirteenth is the entity number for that PAN within that state, so a second registration in the same state gets a 2. The fourteenth is Z, currently unused. The fifteenth is a checksum computed from the first fourteen.
Why does my supplier have several GSTINs?: Registration is state-wise. A business operating in four states holds four GSTINs, all built on the same PAN. The one that belongs on your invoice is the one for the state that made the supply.
How is the check digit calculated?: Each of the first fourteen characters is converted to a value from 0 to 35, multiplied by an alternating factor of 1 or 2 working from the right, and the quotient and remainder of that product divided by 36 are added together. The check character is whatever value brings the running total up to the next multiple of 36.

Last reviewed 2026-09-10. Written and maintained by Kartikeya Mishra.