GST Number Validator

Instantly validate GSTIN formats, verify state codes, and double-checkchecksum validation math.

GSTIN Input

Verification Report

Length Check (15 Chars): -
Format Regex structure: -
State Code check: -
Mathematical Checksum: -

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In-Depth Guide to GSTIN Formats and Modulo 36 Checksum Validation

The Goods and Services Tax Identification Number (GSTIN) is a unique 15-digit alphanumeric identifier assigned to every business registered under the GST Act in India. Validating the GSTIN on vendor invoices is essential for accountants and business owners to ensure accurate tax filings and secure **Input Tax Credit (ITC)**.

Deconstructing the 15-Digit GSTIN Structure

Every GST number is systematically built from government registration data, coded as follows:

[State Code: 2 Digits] [PAN: 10 Chars] [Entity: 1 Digit] [Default: Z] [Check Digit: 1 Digit]
  • State Code (Digits 1–2): Matches the 2011 Census state codes (e.g. `07` for Delhi, `27` for Maharashtra). Our tool cross-references this prefix to identify the registered state.
  • Business PAN (Digits 3–12): The Permanent Account Number mapping the legal entity registered with the Income Tax department (five letters, four numbers, and one check letter).
  • Entity Code (Digit 13): Represents the order of business registrations this entity holds in that state (starts at `1` and increments to `2`, `3` ... then letters `A` to `Z`).
  • Default Digit (Digit 14): Currently set to the letter **`Z`** by default for all GST numbers.
  • Check Digit (Digit 15): A checksum character mathematically computed from the first 14 characters.

The Modulo 36 Checksum Mathematical Algorithm

The government computes the 15th digit using the official **Modulo 36 checksum formula** to catch transcription errors. Alphanumeric values `0–9` evaluate to `0–9`, and letters `A–Z` map to `10–35`. The algorithm assigns weight factors of `1` (for odd indices) and `2` (for even indices) to characters 1 through 14, sums the factored results, and performs modulo-36 division. The remainder defines the 15th validation character.

Because malicious actors can generate fake numbers that happen to pass this mathematical checksum, you should use our **Two-Step Verification Flow**. If our local checksum test passes, click the "Verify Active Status on Govt Portal" button. It copies the GSTIN to your clipboard and redirects you to the official registry search where you can paste the number to confirm the active state of the business in one click.

After verifying your vendor's GSTIN, you can compute exact billing distributions and CGST/SGST splits using our GST Calculator. For validating contact registration details of customers, check out our Email Validator.

Frequently Asked Questions

How do I check if a GST number is mathematically valid?
The first 14 digits of a GST number are computed using a base-36 weight product sum. The resulting remainder is divided by 36 to calculate the 15th character. This tool runs this checksum validation automatically.
How does the live lookup verify fake GST numbers?
If local checksum tests pass, you can click the 'Verify Active Status on Govt Portal' button. This automatically copies the GSTIN to your clipboard and opens the official GST search page where you paste the number to confirm active registry status.