What is GSTIN?

Also called: GST Identification Number

A GSTIN is the fifteen-character number that identifies a business registered under GST, built from the state code, the holder's PAN and a check digit.

The first two characters are the state code — 20 for Jharkhand, 09 for Uttar Pradesh, 10 for Bihar. The next ten are the holder's PAN, which is why GST registration requires a PAN first. The thirteenth is the entity's registration count within that state.

Because the state code is embedded, a business operating in three states holds three GSTINs against one PAN, and files separately for each.

Why it matters

Your customers cannot claim input tax credit without a valid GSTIN on the invoice, so an incorrect one costs them money and you the relationship.

A worked example

Reading a GSTIN issued in Jharkhand: 20ABCDE1234F1Z5.

Illustrative figures. Your own numbers will differ — that is what the quote is for.
Characters 1–2	20 — the state code for Jharkhand
Characters 3–12	ABCDE1234F — the holder's PAN
Character 13	1 — the registration serial for that PAN in that state
Character 14	Z — fixed by default
Character 15	5 — a checksum

Because characters 3 to 12 are the PAN, a GSTIN and an income tax return can be tied together by anyone looking, which is exactly how the department reconciles GST turnover against declared income.

The statutory position

Each figure with the provision it comes from, so it can be checked.
What	Position	Source
Structure	15 characters: 2 state code, 10 PAN, 1 entity serial, 1 default, 1 checksum	Rule 8 read with Rule 10, CGST Rules 2017
One registration per state	A business operating in several states needs a GSTIN in each	Section 25(1), CGST Act 2017
Display obligation	The certificate and GSTIN must be displayed at the principal place of business	Rule 18, CGST Rules 2017

Not to be confused with

These get used interchangeably, including by tools that should know better. They are different things.

GST registration number

They are the same thing — GSTIN is the formal name for the number on the registration certificate. There is no second number.

PAN

The PAN is embedded inside the GSTIN, but the two are issued by different departments for different purposes and are quoted in different places.

ARN

An Application Reference Number is issued when you apply and lets you track the application. It is not a registration and confers no right to charge GST.

Questions people ask

Can I use one GSTIN across states?

No. Registration is state-wise, so stock held in a warehouse in another state needs a registration there. This catches out e-commerce sellers using fulfilment centres, where the platform's warehouse creates a registration obligation in that state.

How do I check whether a supplier's GSTIN is genuine?

The GST portal's search facility returns the legal name, status and registration date for any GSTIN. It is worth doing before claiming credit on a large invoice from a new supplier — a cancelled registration means the credit is not available.

What usually goes wrong

Operating from a second state on the first state's GSTIN
Quoting the GSTIN of a cancelled registration on invoices, so customers cannot claim credit
Typing the GSTIN wrongly on an invoice, which breaks the customer's GSTR-2B match
Not displaying the certificate at the premises, which is a separate contravention