GSTIN format: what the 15 characters mean
Every GST registration number (GSTIN) has the same structure. Take the sample 27AAPFU0939F1ZV:
| Characters | Sample | Meaning |
|---|---|---|
| 1–2 | 27 | State code (27 = Maharashtra) |
| 3–12 | AAPFU0939F | PAN of the business; the 4th PAN letter shows the holder type (F = firm / LLP, C = company, P = individual) |
| 13 | 1 | Number of the registration under this PAN in this state (1 = first) |
| 14 | Z | Default letter, Z for normal taxpayers |
| 15 | V | Check digit, calculated from the first 14 characters |
How GST number validation works
The checker runs the same mod-36 checksum the GST system uses. Each character becomes a value (0–9, then A = 10 … Z = 35); every second value is doubled; each result is split by 36 and the parts are added; the check digit is the character that brings the total to a multiple of 36. A single wrong or swapped character almost always breaks the check, which is why it catches typing errors on purchase bills before you file GSTR-1 or claim input tax credit.
A valid check digit does not prove the registration is active. For that, search the number on the official GST portal (Search Taxpayer on services.gst.gov.in) or press Fetch business name above.
How to verify a GSTIN on the GST portal
- Open services.gst.gov.in and choose Search Taxpayer → Search by GSTIN/UIN. No login is needed.
- Enter the 15-character GSTIN and the captcha.
- Read the legal name, trade name, constitution of business, date of registration, taxpayer type and the GSTIN status (Active, Suspended or Cancelled).
- Match the name and address with the bill. If the status is not Active, talk to the supplier before you claim credit.
The offline check on this page tells you in a second whether a number can exist at all, so you only need the portal for numbers that pass it.
GST state codes list
| Code | State / union territory |
|---|---|
| 01 | Jammu & Kashmir |
| 02 | Himachal Pradesh |
| 03 | Punjab |
| 04 | Chandigarh |
| 05 | Uttarakhand |
| 06 | Haryana |
| 07 | Delhi |
| 08 | Rajasthan |
| 09 | Uttar Pradesh |
| 10 | Bihar |
| 11 | Sikkim |
| 12 | Arunachal Pradesh |
| 13 | Nagaland |
| 14 | Manipur |
| 15 | Mizoram |
| 16 | Tripura |
| 17 | Meghalaya |
| 18 | Assam |
| 19 | West Bengal |
| 20 | Jharkhand |
| 21 | Odisha |
| 22 | Chhattisgarh |
| 23 | Madhya Pradesh |
| 24 | Gujarat |
| 26 | Dadra & Nagar Haveli |
| 27 | Maharashtra |
| 29 | Karnataka |
| 30 | Goa |
| 31 | Lakshadweep |
| 32 | Kerala |
| 33 | Tamil Nadu |
| 34 | Puducherry |
| 35 | Andaman & Nicobar |
| 36 | Telangana |
| 37 | Andhra Pradesh |
| 38 | Ladakh |
| 97 | Other Territory |
| 99 | Centre Jurisdiction |
Older GSTINs can still start with 28 (undivided Andhra Pradesh, now 37) or 25 (Daman & Diu, now merged into 26).
Why does a GST number show as invalid?
- A typing slip: the letter O typed for the digit 0, I for 1, or two characters swapped. The check digit catches almost all of these.
- A missing or extra character: a GSTIN is exactly 15 characters; spaces and dashes are ignored here.
- A PAN or TAN instead of a GSTIN: a 10-character PAN is not a GST number.
- A made-up number: if the supplier's GSTIN fails the check, ask for their registration certificate before you pay a bill with GST on it — input tax credit on a fake GSTIN will be reversed.
Why check a GSTIN before you bill or buy?
- Input tax credit: credit flows only when your supplier's GSTIN is right on the bill and they file their GSTR-1.
- Correct tax type: the first two digits tell you the buyer's state, which decides CGST + SGST or IGST — the GST invoice generator does this for you.
- Clean returns: a mistyped GSTIN in a B2B invoice puts the sale in the wrong place in GSTR-1.
Need the tax for a line item? Use the GST calculator or look the item up in the HSN code finder.