GST · 25 June 2026
What Is a GSTIN? Decoding the 15 Characters on Your Invoice
A GSTIN (Goods and Services Tax Identification Number) is the 15-character code that identifies a registered business under GST. It is not random: it is built from a 2-digit state code, the 10-character PAN of the business, a single entity digit, a default letter, and a checksum. Knowing how it decodes lets you sanity-check the GSTIN on any pakka bill, the field Rule 46 of the CGST Rules lists first on a tax invoice.
By Mrs. Swapna Patel
Last reviewed
25 June 2026
In this section
Answers
- What Is a GSTIN? Decoding the 15 Characters on Your Invoice
- What Is a Pakka Bill? The GST Invoice That Counts as Valid
- What Is a Kaccha Bill? Why the Rough Slip Has No GST Standing
- Why Move From a Kaccha Bill to a Pakka Bill?
- How to Upgrade From a Kaccha Bill to a Pakka Bill (GST Invoice)
- 5 GST Invoice Mistakes That Trigger a Tax Notice (And How to Fix Them)
- 7 Fields Every Skilled Professional Must Put on a GST Invoice: Rule 46 Checklist
- What Makes a GST Invoice Legally Binding — And Why Clients Pay Faster When It Is
- What Is a Bill of Supply? The GST Document Without Tax
- What Is an IRN (Invoice Reference Number) Under GST?
A GSTIN is a random registration number the GST department assigns.
A GSTIN is a structured 15-character code built from your state code and your PAN, so most of it is fixed and predictable, not random. It is the first field Rule 46 of the CGST Rules requires on a tax invoice.
What is a GSTIN?
Short answer
A GSTIN is the 15-character code that identifies a GST-registered business. It is the first thing Rule 46 of the CGST Rules requires on a tax invoice, because it ties the bill to a real, registered seller.
Every business that registers under GST is assigned one GSTIN per state it operates in. The same business can hold several GSTINs across states, but each is built on the same PAN. On an invoice, the GSTIN is what lets a buyer, or the tax department, confirm who issued it.
What do the 15 characters mean?
Short answer
The code splits into five parts: a state code, the business PAN, an entity digit, a fixed letter, and a checksum.
| Position | Characters | What it encodes |
|---|---|---|
| 1-2 | 2 digits | State code (the state where the business is registered) |
| 3-12 | 10 characters | The business's PAN (Permanent Account Number) |
| 13 | 1 character | Entity number, the count of registrations on that PAN in the state |
| 14 | 1 letter | A default letter, currently 'Z', reserved for future use |
| 15 | 1 character | A checksum used to validate the whole number |
The five segments of a 15-character GSTIN
Why does decoding the GSTIN matter?
Short answer
Because the PAN inside the GSTIN must match the seller, and a mismatch on a pakka bill is a warning sign before you claim credit on it.
- The state code tells you where the seller is registered, which feeds into whether the sale is intra-state or inter-state.
- The PAN (positions 3 to 12) should match the seller's name on the invoice. A GSTIN whose PAN does not fit the seller is a red flag.
- A buyer claiming input tax credit relies on the GSTIN being valid, so a wrong or fake GSTIN can put that credit at risk.
How do you verify a GSTIN?
Short answer
Use the Search Taxpayer tool on the official GST portal to confirm a GSTIN is real and active before relying on the invoice.
- Enter the GSTIN on the GST portal's Search Taxpayer page to see the legal name and registration status.
- An invoice with an inactive or cancelled GSTIN is not a safe basis for an input tax credit claim.
- Confirm the GSTIN on a supplier's first invoice; it rarely changes after that.
References & related
Primary sources
- Rule 46, Central Goods and Services Tax Rules 2017 — CBICGSTIN is a mandatory particular on every tax invoice.
- GST registration framework — CBIC GST portalStructure of the GST registration number assigned to a taxpayer.
- Search Taxpayer (GSTIN verification) — GST portal, GSTNOfficial tool to verify a GSTIN and its registration status.
Last reviewed: 25 June 2026