GST number format, explained

The 15-character layout

Every GST registration number follows the same pattern. Read from left to right, the first two characters locate the registration, the next ten identify the taxpayer through its PAN, and the last three distinguish the registration and protect against errors. Below is a sample number used for illustration only.

1. State code27Two digits for the state or union territory where the registration sits. 27 is Maharashtra.
2. PANAAFCE7126DThe ten-character PAN of the business or person. Positions 3 to 7 are letters, 8 to 11 digits and 12 a letter.
3. Entity number1Tells apart several registrations held under the same PAN in one state.
4. Fixed ZZThe 14th character is Z in the standard format. It is reserved for future use.
5. Check characterUA computed character, from 0-9 or A-Z, that helps catch typing mistakes.

Reading the PAN inside a GSTIN

The PAN is the part most people recognise. Its fourth letter says what kind of person or entity holds it, which is useful when you are checking a supplier’s details against a document. In the sample, AAFCE7126D has a C in the fourth position, which marks a company.

The PAN is issued by the Income Tax Department. A GSTIN does not replace it, and an invoice that quotes only the PAN is not a substitute for a GST number where one is required.

Entity number, Z and state codes

The entity number is usually 1 for the first registration a PAN holds in a state. When the same PAN is registered again in that state, for example for another place of business or a separate line of activity, the number moves on to 2, 3 and so on, and then to letters. The fixed Z that follows is a placeholder in the standard format. Its presence is a quick sign that the number is in the correct shape.

For the two digits at the start, use the code list in the GST state code guide. Codes such as 07 for Delhi need their leading zero, and a number that begins with a code belonging to another state suggests the wrong registration was copied.

How the check character is calculated

The final character is not random. It is derived from the first fourteen characters, so a single mistyped letter or digit will usually produce a check character that no longer matches. Here is the method, using the sample number:

1. Give every character a value: digits 0 to 9 keep their value, and A to Z count from 10 to 35.
2. Multiply each value by 1 in odd positions (1, 3, 5 … 13) and by 2 in even positions (2, 4, 6 … 14).
3. Split each product into base-36 parts: the number of full 36s, plus the remainder. Add the two together. A product of 70 becomes 1 + 34 = 35.
4. Add all fourteen results to get a total. In the sample it is 186.
5. Take 186 modulo 36, which leaves 6. Subtract that from 36 to get 30, and the character with value 30 is U.

Common typing mistakes

Most errors come from characters that look alike. The positions have rules, so some slips are obvious once you look at the structure.

If the format check fails, compare the number character by character with the source document before you assume the registration is wrong. The fix is usually a typing error. The bulk GSTIN lookup runs this format and check-character test on every entry before it sends any request, so a typo is caught without using a lookup.

What a valid format does and does not prove

A valid format is a first filter, not a verdict. It tells you that the number is well formed and that its check character agrees with the rest of it. It cannot tell you whether the business is active, whether the registration has been cancelled, or whether a particular invoice is genuine. For those checks, look up the registration on the official GST portal and compare the legal name, trade name and address with your records.

The GST search help page explains GSTIN lookups, business profiles and return records.

Frequently asked questions