What a GSTIN is made of
A GST Identification Number (GSTIN) is 15 characters long. It is built from the state and the business’s PAN, so most of it can be checked without going online.
| Position | Example (27AAPFU0939F1ZV) | Meaning |
|---|---|---|
| 1–2 | 27 | State or UT code (27 = Maharashtra) |
| 3–12 | AAPFU0939F | PAN of the business: 5 letters, 4 digits, 1 letter. The 4th letter is the holder type (C company, P individual, F firm, H HUF…) |
| 13 | 1 | Registration number for this PAN in the state (1 for the first, 2 for the second, then letters after 9) |
| 14 | Z | “Z” by default for normal registrations |
| 15 | V | Check digit calculated from the first 14 characters |
How the check digit works
The 15th character is a check code computed from the first 14. Each character is turned into a number (0–9 stay as they are, A = 10 up to Z = 35). The values are multiplied alternately by 1 and 2, each product is split into its quotient and remainder when divided by 36, and these are added up. The check character is the one that brings the total to a multiple of 36. Because of this, a single mistyped character, or most swaps of two neighbouring characters, produces the wrong check digit and the validator flags it.
We tested the validator against GSTINs that large companies publish on their invoices and websites, and every real number passed while mistyped versions failed.
What the validator cannot tell you
A valid format only proves the number could exist. It does not prove the registration is active, that it belongs to the business in front of you, or that it was not cancelled. Before claiming input tax credit or making a large sale on credit, look the number up on the GST portal’s Search Taxpayer page and check the legal name, trade name, status and date of registration.
State codes
Common codes: 07 Delhi, 08 Rajasthan, 09 Uttar Pradesh, 10 Bihar, 19 West Bengal, 20 Jharkhand, 21 Odisha, 23 Madhya Pradesh, 24 Gujarat, 27 Maharashtra, 29 Karnataka, 32 Kerala, 33 Tamil Nadu, 36 Telangana, 37 Andhra Pradesh. Code 38 is Ladakh, 26 is Dadra and Nagar Haveli and Daman and Diu, 97 is used for Other Territory and 99 for the Centre Jurisdiction.
Common mistakes
- O and 0, I and 1 mixed up. The PAN part is letters-digits-letter in a fixed pattern, so the validator points out where a letter or digit is in the wrong place.
- Old Andhra Pradesh code 28. Businesses in Andhra Pradesh after the 2014 reorganisation use 37; 28 still appears on some old registrations.
- The wrong state on the invoice. The first two digits tell you the buyer’s registered state. If it differs from yours, a supply delivered there is usually inter-state (IGST).
- Using a GSTIN from an old letterhead. Registrations get cancelled; always check the status on the portal for big orders.
Official sources
- GST portal: Search Taxpayer by GSTIN/UIN
- CBIC tax information portal (CGST Act, Rules and notifications): Rule 10 of the CGST Rules (certificate of registration and GSTIN).
Checked on 28 October 2026.