GSTIN Validator & Checksum Checker
Paste any 15-digit GSTIN to verify its format and official check digit live — and decode the state, embedded PAN and entity number instantly.
- Free — no sign-up
- Instant, on-screen results
- Built by our CA · CS team
- Rules cited on the page
Fill in the details — the answer on the right updates as you go.
Position-by-position breakdown
15 positions · format contract| Position | Meaning | Value / Status |
|---|
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Disclaimer: This validator checks GSTIN structure and the official checksum digit only. A structurally valid GSTIN may still be cancelled, suspended or not yet issued. Verify live status on the official GST portal before relying on it for input tax credit.
How a GSTIN is built
A GSTIN (Goods & Services Tax Identification Number) is a 15-character alphanumeric code assigned to every registered taxpayer. It is not random — each block of characters carries meaning, and the final digit is a mathematical check digit that guards against typos.
The format is captured by the regular expression ^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$. Passing this regex means the shape is right; the checksum test below confirms the digits are internally consistent.
The checksum algorithm
The 15th character is a base-36 check digit. It is computed only from the first 14 characters, so any single typo in those characters almost always breaks the checksum — that is what makes it a useful sanity check.
Map to base-36
Each of the first 14 characters is converted to a number: 0–9 → 0–35 and A–Z → 10–35. So "0" is 0, "9" is 9, "A" is 10, "Z" is 35.
Apply the factor
Multiply each value by an alternating factor — 1 for the 1st character, 2 for the 2nd, 1, 2, and so on across all 14 positions.
Fold each product
For every product, compute floor(product / 36) + (product mod 36) and add it to a running total. This "digit-sum in base 36" keeps large products in range.
Derive the check digit
Take (36 − (total mod 36)) mod 36, then map that number back to a character (0–35 → 0–9, A–Z). If it equals the 15th character, the checksum is valid.
Worked example for the default 27AAPFU0939F1ZV: running the 14 characters 27AAPFU0939F1Z through the steps above yields a check digit of V, which matches the 15th character — so it is checksum-valid. Change that last V to any other letter and the checksum test fails immediately.
GST state codes reference
The first two digits identify the state or union territory of registration. These are the official GST state codes (aligned to the 2011 Census codes).
Key terms explained
GSTIN vs GST number
They are the same thing — "GSTIN" is the formal name for the 15-character GST registration number printed on invoices and the registration certificate (Form GST REG-06).
Embedded PAN
Characters 3–12 are the taxpayer's PAN. A GSTIN and PAN should always agree — if the PAN block is malformed, the GSTIN cannot be genuine.
Entity / registration number
Position 13 shows how many registrations that PAN holds in that state. The first registration is "1"; additional ones run 2–9 then A–Z.
Format valid ≠ active
A GSTIN can be perfectly formed and still be cancelled or suspended. Always confirm live status on the GST portal before claiming input tax credit against it.
Questions people ask
Short answers on GSTIN Validator (Checksum). Tap a question to open it.
01How does GSTIN validation work?
A GSTIN is 15 characters: a two-digit state code, a ten-character PAN, an entity code, the letter Z, and a check digit computed from the first fourteen characters using a modulo-36 algorithm. The check digit is what proves the number is well formed.
02Does a valid checksum mean the GSTIN is active?
No. The checksum only confirms the number is structurally correct. A GSTIN can pass the check and still be cancelled or suspended, so verify the status on the GST portal before relying on it.
03Why should I verify a supplier's GSTIN?
Because your input tax credit depends on the supplier being registered and actually reporting the invoice. Dealing with a cancelled GSTIN means the credit will not appear in your GSTR-2B and will be denied.
04Can I check the PAN behind a GSTIN?
Yes — characters 3 to 12 of the GSTIN are the PAN of the registered person, which lets you tie a GST registration to the same entity's income-tax records.
05What if a customer gives me an invalid GSTIN?
Do not issue a B2B invoice against it. Treat the supply as B2C until a valid, active GSTIN is provided, because a wrong GSTIN in GSTR-1 cannot pass credit and will need amendment later.
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Disclaimer: This tool gives indicative results for general guidance only and is not professional advice. Please verify with a qualified CA before acting on the numbers.