What Is a GSTIN and How Is It Structured?

What is a GSTIN and how is it structured?

A GSTIN is the 15-character identification number issued to every person registered under GST in India. The first two characters are the state code, the next ten are the holder’s PAN, the thirteenth indicates the number of registrations that entity holds in that state, the fourteenth is the letter Z by default, and the fifteenth is a checksum character computed from the preceding fourteen.

Reading the fifteen characters

State code, then PAN, then an entity number, then Z, then a check character. Because the PAN sits inside it, two GSTINs belonging to the same legal entity in different states share their middle ten characters — which is a quick way to confirm that two registrations really are the same business.

The check character

The final character is computed from the first fourteen using a modulo-36 algorithm. That means a mistyped GSTIN can usually be detected instantly without contacting the portal at all, which is what a validator does.

Why it matters on an invoice

A B2B tax invoice without a valid customer GSTIN cannot be reported correctly and the customer’s input credit can be challenged. It is the single most common cause of a rejected GSTR-1.

Can one business have more than one GSTIN?

Yes. Registration is state-wise, so an entity operating in four states holds four GSTINs, all sharing the same PAN in characters three to twelve.

How can I tell if a GSTIN is valid?

The format and the check character can be verified offline, which catches almost all typing errors. Whether the registration is currently active is a separate question only the GST portal can answer.

Is the GSTIN the same as a PAN?

No, but it contains one. Characters three to twelve of a GSTIN are the holder’s PAN.