GST Number Format – Decode the GSTIN Structure

If you’ve ever received a tax invoice or filed a GST return, you’ve likely come across a 15-digit code called the GST number. It’s more than just a registration ID—it’s the unique tax identity of every GST-registered business in India. Knowing how to decode this number can help you avoid fraud, validate documents, and stay compliant. Whether you’re a small trader or a large company, understanding the GSTIN structure is essential for smooth business operations.

What is a GST Number (GSTIN)?

A GSTIN, or Goods and Services Tax Identification Number, is a unique 15-digit alphanumeric code assigned to every taxpayer registered under the GST regime. It is mandatory for businesses exceeding the prescribed turnover threshold to obtain a GSTIN. This number is used for all GST-related activities, including filing returns, claiming input tax credit, and issuing invoices. The GSTIN replaces previous tax identification numbers, bringing all indirect tax registrations under a single, unified system.

Format of GST Number in India

The GSTIN is structured as a 15-digit alphanumeric code, where each segment holds specific significance. This structure not only ensures uniqueness but also encodes vital information about the taxpayer, such as their state, PAN, and registration details. Here’s a quick overview of what each part represents:

1. 1–2 digits: State Code
   Represents the state or union territory as per the Indian Census 2011. For example, ‘27’ stands for Maharashtra, ‘07’ for Delhi, and ‘29’ for Karnataka.
2. 3–12 digits: PAN of the Business or Entity
   These ten characters are the Permanent Account Number (PAN) of the business or individual. PAN is mandatory for GST registration.
3. 13th digit: Entity Code
   Indicates the number of registrations a business entity has within a state under the same PAN. For the first registration, it is ‘1’; for the second, ‘2’, and so on. After ‘9’, it continues with the alphabet's ‘A’ to ‘Z’.
4. 14th digit: Default ‘Z’
   This digit is kept as ‘Z’ for all regular taxpayers. It is reserved for future use or special categories.
5. 15th digit: Checksum Digit
   This is an alphanumeric character used as a checksum for error detection, ensuring the authenticity of the GSTIN.

Example of a GSTIN and Explanation

Let’s take a sample GSTIN: 27ABCDE1234F1Z5

1. 27 – State code for Maharashtra
2. ABCDE1234F – PAN of the business
3. 1 – First registration under this PAN in Maharashtra
4. Z – Default value
5. 5 – Checksum digit

This GSTIN indicates that the business is registered in Maharashtra, with a PAN of ABCDE1234F. It is their first GST registration in the state, and the GSTIN is valid according to the checksum.

Also Read : Benefits of Filing Income Tax Return (ITR) 2025

How to Verify a GST Number Online?

To ensure authenticity, it’s important to verify GST numbers, especially when dealing with new vendors or partners. You can do this in just a few steps:

1. Visit the official GST Portal:www.gst.gov.in
2. Click on ‘Search Taxpayer’ and select ‘Search by GSTIN/UIN’.
3. Enter the GSTIN and the captcha code, then click ‘Search’.
4. The portal will display the business’s legal name, registration status, and other details if the GSTIN is valid .

If valid, the portal will display details like the business name, registration status, type of taxpayer, and address.

Importance of Understanding GSTIN Structure

Here’s why decoding and validating the GST number is important:

1. Avoiding Fraud: Verifying GSTIN helps you avoid fraudulent invoices and fake tax credits.
2. Accurate Filing: Entering the correct GSTIN ensures that input tax credits are allocated to the correct party.
3. Invoice Compliance: Using the correct GST number structure is mandatory for legal invoicing and helps avoid penalties.
4. Tracking Transactions: Authorities use GSTIN to track transactions across states and maintain transparency.

Businesses that wrongly record GSTINs may lose tax credits or attract notices from tax departments.

Difference Between GSTIN and GSTN

The Goods and Services Tax Identification Number (GSTIN) and the Goods and Services Tax Network (GSTN) are two key terms frequently used in India’s GST system. While they may sound similar, they serve distinctly different purposes within the tax ecosystem.

Understanding the distinction between GSTIN and GSTN helps businesses navigate GST compliance smoothly and leverage the system effectively.

How to Spot Fake GST Numbers?

Fake GST numbers are commonly used in fraudulent invoices, so verifying them is crucial. Here are key ways to identify fake GSTINs:

1. Check Format: Ensure the GSTIN follows the correct 15-digit structure — state code (2 digits), PAN (10 characters), entity number, default letter ‘Z’, and checksum digit.
2. Verify Online: Use the official GST portal (www.gst.gov.in) or trusted third-party tools to check GSTIN validity and business details.
3. Match Business Information: Confirm that the GSTIN matches the supplier’s name and address as listed on the invoices.
4. Check Registration Status: Ensure the GSTIN is active, not suspended or deregistered.
5. Monitor Filing History: Look for consistent GST return filings by the supplier.

Always report suspicious GSTINs to the GST authorities for action. Verifying GST numbers helps prevent fraud and ensures smooth, compliant business transactions.

Conclusion

Decoding the GSTIN structure empowers businesses and individuals to verify the authenticity of GST numbers, avoid fraud, and ensure proper tax compliance. Always check the GSTIN on the official portal before entering into business transactions or claiming input tax credit. This verification process helps confirm the taxpayer’s legal name, registration status, and business details—essential steps not only for compliance but also when applying for a business loan, where accurate GST data supports loan eligibility. Using the official GST portal or trusted verification tools ensures accuracy and protects your business interests. Staying vigilant with GSTIN validation promotes transparency and smooth compliance in India’s tax ecosystem.

FAQs

Q.1. What does each digit in the GSTIN represent?

A. The first two digits are the state code, the next ten are the PAN, the 13th is the entity number, the 14th is a default ‘Z’, and the 15th is a checksum digit.

Q.2. How can I check if a GST number is valid?

A. Visit the GST portal (www.gst.gov.in), use the ‘Search Taxpayer’ feature, enter the GSTIN, and view the registration details.

Q.3. Is GSTIN the same as a GST registration number?

A. GSTIN is the official registration number assigned to every GST-registered taxpayer.

Q.4. Can a business have more than one GSTIN?

A. A business can have multiple GSTINs if it operates in more than one state or has multiple business verticals in the same state. Each registration will have a unique 13th digit in the GSTIN.

Q.5. Is PAN mandatory for GST registration?

A. Yes, PAN is mandatory for GST registration, except for non-resident taxable persons, who may use a different identification number.

Q.6. What should I do if I find an invalid GSTIN on an invoice?

A. Do not proceed with the transaction. Report the issue to the concerned authorities and verify with the supplier.

Disclaimer:

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