A GSTIN is the number a business gets when it registers under GST. It goes on every tax invoice, every return and every e-way bill, and a buyer needs your GSTIN on the invoice to claim input tax credit.
How the 15 characters are built
| Position | What it holds | Example |
|---|---|---|
| 1 to 2 | State code | 24 for Gujarat |
| 3 to 12 | The business's PAN | AABCP1234Q |
| 13 | Entity number for the same PAN in that state | 1 |
| 14 | Z by default | Z |
| 15 | Check character | 5 |
So 24AABCP1234Q1Z5 belongs to a business in Gujarat. The same company registered in Maharashtra would have a GSTIN starting with 27 and the same PAN in the middle.
Why it matters day to day
The first two digits of your GSTIN and your buyer's GSTIN decide whether an invoice carries CGST and SGST or IGST. A wrong digit in a buyer's GSTIN means their credit does not show in their GSTR-2B, and the correction falls on you. You can check any GSTIN on the search page of the GST portal before you bill a new party.
Registration is needed once turnover crosses the threshold, ₹40 lakh for most goods suppliers and ₹20 lakh for service providers, with lower limits in some states (as of October 2026), and from the start for inter-state sellers of goods and most e-commerce sellers.