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GST Number Validator

Finance & Global IDs

Check if a GST number follows the correct 15-character format — state code, PAN, entity code, and checksum. Runs in your browser, no signup needed.

Reviewed by the thecalcu.com team · Last updated July 19, 2026

What is a GST?

A GST Number Validator checks whether a GSTIN (Goods and Services Tax Identification Number) conforms to the official 15-character format defined by the Goods and Services Tax Network (GSTN). GST was introduced in India on 1 July 2017 as a unified indirect tax, replacing a patchwork of central and state levies including VAT, service tax, and excise duty. Every business that registers under GST, mandatory above the prescribed turnover threshold, receives a unique GSTIN that identifies the taxpayer, their state, and their PAN.

A GSTIN is not a random identifier: each of its 15 characters carries specific meaning. The first two digits encode the state code (01–37), the next ten characters are the taxpayer's PAN number, the thirteenth character is an entity number for businesses with multiple registrations in one state, the fourteenth is always the letter Z, and the fifteenth is an alphanumeric checksum. A single character in the wrong position or character class makes the entire number invalid.

This validator checks the format of the GSTIN instantly as you type. It also breaks down each segment, telling you the state the number corresponds to, the embedded PAN portion, and the entity and checksum characters, so you can spot exactly where a typo occurred.

Important: format validation confirms the structure is correct; it does not verify that the GSTIN is currently registered, active, or in good standing with the GSTN portal. For live registration lookup, use the official GST portal. For related Indian financial ID validation, see the PAN Validator.

Why Use a GST Number Validator?

Entering or copying a GSTIN incorrectly is a common and costly mistake. An invalid GSTIN on a tax invoice means the buyer cannot claim the Input Tax Credit (ITC) for that purchase, a direct financial loss. Similarly, filing a GSTR return with an incorrect supplier GSTIN causes a mismatch that the GSTN flags and requires an amendment.

Common situations where format errors cause problems:

  • A vendor provides their GSTIN verbally or in a chat message and a digit or letter is transposed during entry into your accounting software
  • An e-commerce seller onboarding a new vendor collects GSTINs via a form and wants to catch format errors at submission rather than during invoice reconciliation
  • A developer building a billing or ERP system needs to validate GSTINs at the point of data entry before the record is saved
  • An accountant reconciling GSTR-2A with purchase invoices wants to quickly confirm which supplier GSTINs are structurally malformed

A single validation step before the number is used, in an invoice, a return, or a vendor record, prevents downstream corrections that require portal amendments and often involve penalties or delayed ITC claims. Use the GST Calculator to compute tax amounts once you have confirmed the GSTIN is valid.

Who Should Use This Validator?

Accountants and tax professionals handling GST invoicing, return filing, and ITC reconciliation, confirm vendor GSTINs before entering them into accounting software to prevent GSTR-2A mismatches.

E-commerce and marketplace operators onboarding sellers, validate GSTINs at registration to catch typos before they propagate into invoices and returns.

Developers building billing, ERP, or procurement systems, add GSTIN format validation to the data-entry layer, using the same regex this tool implements.

Business owners and sole proprietors who issue or receive GST invoices and want to confirm the GSTIN printed on a document is structurally correct before accepting it.

Startups and small businesses new to GST who want to understand the format of their own GSTIN, the segment breakdown makes the structure legible for the first time.

If you need to verify the embedded PAN, use the PAN Validator. To calculate the GST amount on a transaction, use the GST Calculator.

What Insights Does the GST Validator Give You?

When the GSTIN is valid, the validator provides a full segment breakdown:

  • State, the two-digit state code and the corresponding state name (e.g. 29, Karnataka)
  • PAN portion, the 10-character PAN embedded in characters 3–12
  • Entity number, the registration sequence for this entity in that state
  • Checksum, the final alphanumeric character

This breakdown is useful when you receive a GSTIN and want to confirm it is registered in the expected state, or when you want to extract the PAN portion for cross-referencing.

When the GSTIN is invalid, the validator identifies the specific rule that failed, wrong length, invalid state code, PAN portion in the wrong format, or wrong character in position 14.

Scope: format validation only. The validator cannot tell you whether the GSTIN is currently active, whether the business has filed returns, or whether the registration has been cancelled or suspended.

How to use this GST calculator

  1. Open the GST Number Validator on this page.
  2. Type or paste the GSTIN into the GST Number field. The validator automatically converts lowercase letters to uppercase, so you do not need to manually capitalise.
  3. The result badge updates instantly. A green Valid badge confirms the GSTIN matches the correct 15-character format.
  4. If the badge shows Invalid, read the error message, it specifies whether the length is wrong, the state code is out of range, or a specific segment has the wrong character pattern.
  5. Fix the character that is causing the failure, common issues are a digit where a letter is expected in the PAN portion, a wrong state code, or a missing character, and the badge updates immediately.
  6. For a valid GSTIN, review the segment breakdown in the details section to confirm the state code and embedded PAN match what you expect.

Formula & Methodology

The validator applies the official GSTN format rule using a regular expression:

/^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$/

| Position | Characters | Rule |
|---|---|---|
| 1–2 | State code | Two digits, 01–37 |
| 3–7 | PAN letters | Five uppercase letters (A–Z) |
| 8–11 | PAN digits | Four digits (0–9) |
| 12 | PAN check letter | One uppercase letter (A–Z) |
| 13 | Entity number | One character: 1–9 or A–Z |
| 14 | Fixed | Must be Z |
| 15 | Checksum | One alphanumeric character (0–9 or A–Z) |

Valid example: 29ABCDE1234F1Z5
State: 29 (Karnataka) | PAN: ABCDE1234F | Entity: 1 | Fixed: Z | Checksum: 5

Invalid example: 99ABCDE1234F1Z5
State code 99 is outside the valid range of 01–37, making the GSTIN invalid.

The check is synchronous and purely client-side, no external API calls are made. The state name lookup uses a static map of Indian state codes defined in GST rules.

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Frequently Asked Questions

A GST Number Validator checks whether a GSTIN (Goods and Services Tax Identification Number) follows the correct 15-character format prescribed by the GSTN (Goods and Services Tax Network). Every registered business in India is assigned a unique GSTIN when they register under GST. This tool verifies the structural format of that number, it does not confirm whether the GSTIN is currently active or registered with the GSTN portal.
A GSTIN is exactly 15 characters long: the first two digits are the state code (01–37), characters 3 to 12 are the taxpayer's PAN number (5 uppercase letters, 4 digits, 1 uppercase letter), character 13 is the entity number (1–9 or A–Z, used when a business has multiple registrations in the same state), character 14 is always the letter Z, and character 15 is an alphanumeric checksum.
Each segment of a GSTIN carries specific information. The two-digit state code identifies the state of registration (for example, 29 is Karnataka, 27 is Maharashtra, 07 is Delhi). The next 10 characters are the taxpayer's PAN, linking the GST registration directly to the income tax record. The entity number (character 13) distinguishes multiple registrations held by the same entity in one state. Character 14 is a fixed 'Z', and character 15 is a checksum digit.
No. This validator checks that the number follows the correct 15-character format, state code, PAN structure, entity code, Z, and checksum position. It does not connect to the GSTN portal or any government database. To verify whether a GSTIN is active and registered, visit the official GST portal at gst.gov.in and use the 'Search Taxpayer' feature.
Your GSTIN appears on your GST registration certificate issued by the GSTN after successful registration. It is also printed on your GST invoices (mandatory for B2B supplies), your e-way bills, and your GSTR filings. If you are a buyer verifying a vendor's GSTIN, ask for their registration certificate or check the invoice they have issued you.
No. Validation runs entirely inside your browser. Your GSTIN is never sent to any server, stored, or logged. The check is performed client-side using a regex pattern applied to the text you enter. You can safely validate your own or a vendor's GSTIN without any privacy concern.
The first two digits of a GSTIN identify the Indian state or union territory where the business is registered. For example, 07 is Delhi, 27 is Maharashtra, 29 is Karnataka, and 33 is Tamil Nadu. State codes run from 01 (Jammu & Kashmir) to 37 (Andhra Pradesh). If a number starts with a code outside 01–37, it is not a valid GSTIN.
Yes. A business operating in multiple states must obtain a separate GST registration, and therefore a separate GSTIN, in each state where it has a presence (office, warehouse, or supply point). A business can also have multiple registrations within a single state if it has distinct business verticals. In both cases, the entity number (character 13 of the GSTIN) distinguishes each registration.
GSTN (Goods and Services Tax Network) is the government-owned technology company that manages the IT infrastructure for the GST system in India, the portal, invoicing, returns, and the taxpayer database. GSTIN (Goods and Services Tax Identification Number) is the unique 15-character identifier assigned to each registered taxpayer. This validator checks the format of a GSTIN.
A GSTIN can be structurally valid (correct format) but still be rejected because: the registration has been cancelled or suspended, the PAN embedded in the GSTIN does not match the taxpayer's records, or the business has not filed returns and the portal has flagged the registration. Format validation cannot catch these conditions, only a live GSTN lookup can confirm active status.
A GSTIN embeds the taxpayer's PAN directly as characters 3–12. This design links GST registration to income tax records automatically. If the PAN portion of a GSTIN is structurally incorrect (wrong character pattern), the GSTIN itself will fail format validation. Use the [PAN Validator](/pan-validator-india/) to check the PAN portion separately if needed.
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