As known to all, GSTIN (Goods and Services Tax Identification Number) is a 15 digit ID.
Knowing the structure of the GSTIN is important for a business for the following reasons:

1. To ensure that one’s suppliers have quoted the correct GSTIN in their invoices
2. To ensure that one mentions their own GSTIN correctly in invoices to customers – as input tax credit is dependent on this
3. To ensure that appropriate tax (whether IGST or CGST and SGST) are charged .e.g. If Supplier state code and “Place of supply” state code are different, then IGST will be charged

The 15 digit ID comprises of –

1. 2 digits signifying the state code;

Digit 1 and 2: GST State Code List of India: This state code list under GST, is prescribed as per the Indian Censes of 2011, and is as follows:

2. 10 digit PAN number;

Digits 3 – 12 represent the PAN of the entity, so that a nexus can be established between the GST and the PAN database.

3. 1 digit signifying number of registrations;

Digit 13 is Entity code, which signifies number of registration that an entity has taken within a particular state. It would be pertinent to note that a new registration in a different state will have GSTIN starting with a different state code. A registered person with single registration within a State would have number 1 as 13th digit of the GSTIN. If the same registered person gets a second registration for a second business in the same State, the 13th digit of GSTIN assigned to this second entity would be 2  and so on.

4. 2 digits having default and checksum values

Last two digits are for the purpose of check digit.