What Is a GSTIN? The 15 Digits of a GST Number Explained

A GSTIN (Goods and Services Tax Identification Number) is a unique 15-character code assigned to every GST-registered business in India. The first 2 digits are the state code, the next 10 are the business's PAN, the 13th is the entity/registration number, the 14th is "Z" by default, and the 15th is a check digit.

The structure, digit by digit

• Digits 1–2: State code (e.g. 27 = Maharashtra, 24 = Gujarat, 29 = Karnataka, 33 = Tamil Nadu).
• Digits 3–12: The 10-character PAN of the business or owner.
• Digit 13: Entity number — how many registrations the PAN holds in that state.
• Digit 14: Usually "Z" (reserved).
• Digit 15: A check digit used to validate the whole number.

Why the format matters

Because the structure is fixed, you can sanity-check a GSTIN at a glance: the state code should match where the business operates, and the embedded PAN should match the business's PAN. A number that breaks the format is invalid.

Read the reputation, not just the registration

Knowing a GSTIN is genuine is step one. Step two is knowing if they pay. Look up any GSTIN on HisaabScore to see both. Also read: How to check a GST number online.