A GSTIN — Goods and Services Tax Identification Number — is the unique 15-digit number assigned to every business registered under GST in India. It identifies the taxpayer, shows which state they are registered in, and is built around their PAN. You will find it on every GST invoice. Before you trust a vendor's GSTIN, you can verify it free on the GST portal — and you should, because it protects your input tax credit.
What is a GSTIN?
A GSTIN is a 15-digit alphanumeric code issued to each business registered under GST. It is unique to a taxpayer within a state and is derived from the business's PAN. Every registered seller must show their GSTIN on tax invoices, and buyers use it to claim input tax credit. One PAN can hold multiple GSTINs across different states.
Think of it as the GST equivalent of a registration plate: one number that tells the system exactly who is being taxed and where. For the wider context, see our pillar guide, GST for small businesses in India.
How is the 15-digit GSTIN format decoded?
The GSTIN is not random. Each part carries meaning, and once you know the structure you can read a lot from it.
- Digits 1–2 — State code: the numeric code of the registration state. For example, 27 is Maharashtra and 24 is Gujarat.
- Digits 3–12 — PAN: the 10-character PAN of the business or person.
- Digit 13 — Entity code: the number of registrations the entity has on the same PAN within that state.
- Digit 14 — default letter: currently set to "Z" for most taxpayers.
- Digit 15 — Check digit: a checksum used to validate the number.
So a GSTIN beginning with 27 followed by a PAN tells you the business is registered in Maharashtra under that PAN. This structure is stable and defined by the GST law.
How do you verify a GSTIN on the GST portal?
Verifying a GSTIN takes under a minute and is free. Do this before you record a new vendor.
- Go to gst.gov.in.
- Open the "Search Taxpayer" option and choose "Search by GSTIN/UIN".
- Enter the 15-digit GSTIN exactly as printed on the invoice.
- Complete the on-screen captcha and submit.
- Read the result — it shows the legal name, trade name, registration status (active or cancelled), state, and the type of taxpayer.
Check that the name and state match the vendor you are dealing with, and that the status is active. A cancelled or suspended GSTIN is a red flag.
Why does verifying vendor GSTINs protect your input tax credit?
This is the part that hits your money. Input tax credit (ITC) — the GST you have already paid on purchases — can only be claimed if your supplier is genuinely registered and actually files their returns.
If you book a purchase against a fake, cancelled or wrong GSTIN, you cannot claim the credit. Worse, if a supplier collects GST from you but never deposits it, your credit can be reversed and you may face interest. Verifying upfront filters out the risky vendors before the money leaves your account.
A quick verification habit pays for itself the first time it catches a bad number. To understand the credit rules end to end, read input tax credit for startups.
Managing many vendors makes manual checks tedious. Invodo stores vendor GSTINs against each record so your purchase and invoice data stays clean — see what the platform offers on our features page.
What should you do if a GSTIN is invalid?
If the portal returns an error or the details do not match, do not raise or accept the invoice as-is. Take these steps.
- Re-check the digits: a single mistyped character fails the check. Compare against the printed invoice carefully.
- Ask the vendor: they may have given an old GSTIN, or one registered in a different state.
- Check the status: if it shows cancelled or suspended, the vendor cannot legally charge GST under that number.
- Hold the credit: do not claim ITC on a purchase you cannot verify.
If a number stays invalid and the vendor cannot explain it, treat the GST component as unrecoverable and reconsider the relationship. When in doubt, confirm using the official tool on gst.gov.in or ask your CA.
Why your own GSTIN matters on every invoice
Verification runs both ways. Just as you check your vendors, your customers check you. A correct, active GSTIN printed clearly on your invoice is what lets your buyers claim their credit — and keeps them coming back.
Get your GSTIN onto every invoice automatically, with the right format and tax split, using Invodo. Explore the features and make GSTIN errors a thing of the past.
Put this into practice with Invodo
GST-compliant invoicing, e-invoicing, and purchase management built for Indian businesses.
Invodo Editorial
Reviewed by a Chartered Accountant
The Invodo editorial team writes practical, India-specific guides on GST and business finance. Compliance content is reviewed by a practising Chartered Accountant.
