How a GSTIN is built
A GSTIN (GST Identification Number) has 15 characters. Each part means something, which is why a format check can catch many errors before you put a wrong number on an invoice or e-way bill.
| Characters | Part | What it contains |
|---|---|---|
| 1–2 | State code | The GST state code where the person is registered (for example 24 for Gujarat) |
| 3–12 | PAN | The holder’s PAN: 5 letters, 4 digits, 1 letter. The 4th letter shows the holder type |
| 13 | Entity number | 1–9, then A–Z: the count of registrations under the same PAN in that state |
| 14 | Default letter | “Z” for regular registrations |
| 15 | Check character | Calculated from the first 14 characters |
Check character formula
Each of the first 14 characters is given a value (0–9 for digits, 10–35 for A–Z). Values in odd positions are multiplied by 1 and in even positions by 2. Each product is split into quotient and remainder when divided by 36, and both are added to a running total. The check character is the one whose value equals (36 − total mod 36) mod 36.
Example (illustrative)
A Rajkot pipe manufacturer is given a buyer’s GSTIN over the phone and types 24ABCDE1234F1Z followed by the last character. The tool reads 24 as Gujarat, ABCDE1234F as the PAN (its 4th letter, D, is not one of the standard holder-type letters, so it shows “Other”), 1 as the first registration and Z as the default letter. If the last character does not match the calculated check character, the tool tells you which character it expected, a strong sign that one character was misheard.
Common mistakes
- Confusing the letter O with zero, or I with one, especially in the PAN part.
- Treating a “valid format” result as proof that the buyer is registered. Always check live status on the GST portal for new parties.
- Using a GSTIN from another state for the same business. The state code must match the registration that is actually supplying or receiving the goods.
Bulk check
Switch to Bulk to paste up to 500 GSTINs, one per line or as a column copied from Excel or a CSV file with a “GSTIN” header. Each row shows status, state, PAN and the reason for any error, and repeated GSTINs are flagged. Download the result as CSV to fix your customer master before filing returns.
In the E-Way Easy app, entering a buyer’s GSTIN fills in the buyer name, address, state and PIN automatically, which avoids most typing errors in the first place.