A GSTIN that is typed wrongly once tends to stay wrong everywhere: on invoices, on returns and in your vendor master. The fix is to check the number when it is entered. Manage validates a GSTIN in the company form and in the Business ID screen, and this guide explains what a GSTIN is made of, what the check catches and what to do when a number is refused.
What a GSTIN is made of
A GSTIN has 15 characters. Reading from the left:
- Characters 1–2: the two-digit state code.
- Characters 3–12: usually the holder's PAN (five letters, four digits, one letter).
- Character 13: the registration count of that PAN within the state.
- Character 14: usually the letter Z.
- Character 15: a check character worked out from the first 14.
The check character is what makes a typing slip detectable. It is calculated from the other 14 characters using a checksum method known as Luhn mod 36, so changing one character, or swapping two, almost always makes the last character stop matching.
Not every GSTIN carries a PAN
Most regular taxpayers have their PAN inside the GSTIN, but not all. A tax deductor, for example, registers on its TAN, so a GSTIN such as 07DELA12345B1DE has a TAN in positions 3 to 12. Special registrations can have layouts of their own. A rule that insists on a PAN pattern would wrongly refuse these numbers, so a better check looks at the part every GSTIN has: the state code, 13 letters or digits and a matching check character.
What Manage checks
Manage applies one GSTIN rule in the company form and in Business ID, on the browser and on the server. A GSTIN is accepted when it:
- has 15 characters, starting with a two-digit state code followed by 13 letters or digits;
- ends with a check character that matches the first 14 characters.
Entries are saved in capitals, so you do not need to worry about case.
The company form also lets you enter several GSTINs, separated by commas. If one of them fails, the message names that GSTIN, so you do not have to hunt through the list. When the company's PAN is filled in, a GSTIN that does carry a PAN must carry the same one; a TAN-based GSTIN is not held to this.
What the messages mean
You seeWhat to check GSTIN must be 15 characters, with a two-digit state code followed by 13 letters or digitsA missing or extra character, a space or a dash, or letters in the state code. GSTIN does not add up: its last (check) character does not match the restOne character is probably mistyped. Compare it with the registration certificate or the GST portal. Each GSTIN should contain the PAN above (characters 3 to 12)The GSTIN belongs to a different PAN than the one in the form, or the PAN has a typo.Why one wrong character is costly
A mistyped GSTIN rarely fails on the day you enter it. It shows up later: a customer's GSTR-2B does not show your invoice against their registration, a supplier's invoice cannot be matched to your purchase books, or a notice asks you to explain a mismatch. Each of these takes far more time to untangle than the few seconds it takes to check the number at entry. Catching the slip at the form means the record you build on is already clean, which makes later reconciliation simpler. Our guide to GSTR-2B versus purchase register mismatches shows how such problems surface.
A quick routine for entering a GSTIN
- Copy the number from the registration certificate or the GST portal instead of retyping it.
- Enter the company's PAN first, so a mismatch is caught at once.
- If the check character is refused, read the number back from the source character by character. Look at 0 and O, 1 and I, and 5 and S in particular.
- Save, and confirm that the number looks the way the certificate shows it.
Business ID: the same rule, with clear messages
In Manage you create a Business ID, which maps to the companies you own. Its PAN and GSTIN fields are optional, but when you fill them in, the PAN must read like AAAAA9999A and the GSTIN must pass the check above. A refusal comes back as a sentence naming the field, shown on the Business ID screen, instead of a vague "could not save". Details saved before these rules were added are read back unchanged, and are checked only when their owner saves them again.
A check is not a registration lookup
Passing the check tells you the number is well-formed. It does not tell you that the registration is active or that it belongs to the party you think it does. Before you rely on a supplier or customer GSTIN for input tax credit or an invoice, verify it on the GST portal. See our GST tax invoice checklist for where the GSTIN appears on an invoice.
Key takeaways
- A GSTIN has 15 characters: state code, 13 letters or digits, and a check character.
- Not every GSTIN contains a PAN; TAN-based ones do not.
- Manage uses one rule for the company form and Business ID, and says which part is wrong.
- A valid-looking number still needs verification on the GST portal.
If you manage several companies under one login, Manage keeps each company's identifiers in one place. Our guide on workspace team and Company users explains who can open and edit them. For specific cases, please confirm with your chartered accountant.
