GSTIN Verifier — Format & Mod-36 Checksum

A GSTIN is a 15-character alphanumeric ID issued by GSTN. The first 2 digits are the state code (01 = Jammu & Kashmir, 27 = Maharashtra, 29 = Karnataka, 33 = Tamil Nadu, etc.). Characters 3-12 are the taxpayer's 10-character PAN. Character 13 is the entity number (how many GSTINs this PAN already has in the same state — usually '1'). Character 14 is reserved as 'Z'. Character 15 is a Mod-36 checksum that verifies the previous 14 characters.

GSTN uses the charset 0-9 then A-Z (36 symbols, indexes 0-35). For each of the first 14 characters, multiply its index by 1 if its position is odd-indexed (1st, 3rd, 5th... in 1-based counting) or by 2 if even-indexed. For each product, take quotient + remainder when divided by 36, and add to a running sum. The check digit is (36 − (sum mod 36)) mod 36, looked up back in the charset. This catches almost all single-character typos and most digit transpositions.

Yes. A single PAN can have one GSTIN per state where the business has operations or warehousing — and within a state, separate GSTINs per business vertical (since 2017 GST rules). The 13th character of the GSTIN counts these: the first registration for a PAN in a state is 1, the second is 2, ..., 9, then A, B, ..., up to Z (so up to 35 registrations per PAN per state). This is why two GSTINs from the same company can share characters 3-12 but differ in 1-2 and 13.

Always before filing a GSTR-1 with their invoice. A wrong GSTIN means your buyer will not be able to claim Input Tax Credit, which usually leads to payment disputes and amended returns. Verify at three points: (1) when onboarding a new vendor or B2B customer, (2) before issuing or accepting the first invoice, and (3) periodically — businesses get cancelled, so an annual sweep of your master data prevents nasty surprises during reconciliation.

No. A valid checksum only proves the GSTIN is well-formed — i.e., it could plausibly have been issued. It does not prove the business is currently registered, active, or compliant. For real-time status (Active / Cancelled / Suspended / Provisional), legal name, principal place of business, and return-filing history, you must hit the official GST portal at gst.gov.in or use a paid GSTN-authorised API. This tool covers step 1 (cheap, instant); the portal covers step 2 (slow, definitive).

The Mod-36 checksum is excellent at catching single-character substitution (typing O instead of 0, I instead of 1, 5 instead of S, B instead of 8) and most adjacent transpositions inside the PAN block. It will also catch wrong state codes outside 01-37, missing characters (any length other than 15), and the missing 'Z' in the 14th position. It will not catch errors that happen to produce a valid checksum by accident — those are statistically rare (~1 in 36) but possible, which is why a final lookup on gst.gov.in is the right belt-and-braces approach for high-value transactions.