GSTIN Number Format: What Each of the 15 Characters Means

Every registered business in India gets a GSTIN — a 15-character number that must appear on its tax invoices, returns and e-way bills. The number is not random: each part encodes something, and the last character is a check digit that catches most typing mistakes.

Knowing the GSTIN format helps you spot errors before they reach your invoice or GSTR-1, where a wrong customer GSTIN can cost that customer their input tax credit.

What is a GSTIN?

GSTIN stands for Goods and Services Tax Identification Number. It is issued when your GST registration is approved and is printed on the registration certificate (Form REG-06). It is based on your PAN and your state, which is why one business can hold several GSTINs — one per state, and sometimes more than one within a state.

You will need a GSTIN — yours and often your customer's — on:

• tax invoices, debit notes and credit notes,
• e-invoices (the IRP validates both GSTINs),
• e-way bills,
• returns such as GSTR-1 and GSTR-3B.

How is a GSTIN structured?

A GSTIN has 15 characters in five parts:

Position	Length	Meaning	Example (27AAAPA1234A1Z5)
1–2	2 digits	State code (as per Census 2011 coding)	27 = Maharashtra
3–12	10 characters	PAN of the registered person	AAAPA1234A
13	1 character	Entity number — registrations of that PAN in the same state	1 = first registration
14	1 character	Reserved; "Z" by default	Z
15	1 character	Check character (checksum)	5

Characters 1–2: state code

The first two digits tell you the state or union territory in which the registration is held. This is how you know whether a supply to that customer is likely intra-state or inter-state — though the final answer depends on the place of supply, not just the GSTIN.

Characters 3–12: PAN

The middle ten characters are the PAN of the business. The fourth character of a PAN indicates the type of holder — for example P for an individual, F for a firm, C for a company, H for a HUF, and T for a trust. In the GSTIN this falls at position 6. So if a customer claiming to be a private limited company gives you a GSTIN with "P" at position 6, the registration is in an individual's PAN, which is worth a second look.

Character 13: entity number

This shows how many registrations the same PAN holds in the same state. It is commonly a digit for the first few registrations and continues with letters after that. Most small businesses have "1".

Character 14: "Z" by default

Reserved for future use. Normal registrations carry "Z".

Character 15: check character

Calculated from the first 14 characters using a checksum algorithm. If any single character is mistyped, the check character will usually no longer match, which is how GSTIN validators catch typos without contacting the portal.

GST state codes table

These are the codes you will see most often:

Code	State / UT	Code	State / UT
01	Jammu and Kashmir	21	Odisha
02	Himachal Pradesh	22	Chhattisgarh
03	Punjab	23	Madhya Pradesh
04	Chandigarh	24	Gujarat
05	Uttarakhand	27	Maharashtra
06	Haryana	29	Karnataka
07	Delhi	30	Goa
08	Rajasthan	32	Kerala
09	Uttar Pradesh	33	Tamil Nadu
10	Bihar	34	Puducherry
18	Assam	36	Telangana
19	West Bengal	37	Andhra Pradesh
20	Jharkhand	38	Ladakh

The full list includes all states and UTs, and code 97 is used for "Other Territory" and 96 for "Foreign Country" in certain e-invoice and return fields. Your billing system should use the same codes when it prints the state code next to the place of supply.

Worked example: decoding a customer's GSTIN

A Nagpur electrical distributor receives a purchase order with GSTIN 29ABCFR4321K2Z8 (illustrative). Reading it:

1. 29 — the customer is registered in Karnataka. The distributor is in Maharashtra (27), so for goods delivered to Karnataka the supply is inter-state and IGST applies.
2. ABCFR4321K — the PAN. The fourth PAN character is F, so the customer is a firm (partnership).
3. 2 — this is the firm's second registration in Karnataka, perhaps a separate branch registered as a distinct business vertical.
4. Z — default.
5. 8 — the check character.

On a ₹2,40,000 order at 18%, the distributor raises an invoice with IGST of ₹43,200, total ₹2,83,200, and prints the customer's GSTIN, the place of supply "29 – Karnataka", and its own GSTIN beginning 27.

If the clerk had typed 29ABCFR4321K2Z3, the check character would not match and a validator would reject it before the invoice was saved — exactly the kind of error that otherwise surfaces months later when the customer complains that the invoice is missing from their GSTR-2B.

How to validate a GSTIN

Validation happens in two layers:

1. Format and checksum check. Confirms 15 characters, the right pattern (2 digits, 5 letters, 4 digits, 1 letter, 1 alphanumeric, Z, 1 alphanumeric) and a correct check character. Instant and offline. Try our GSTIN validator.
2. Portal search. On gst.gov.in, use Search Taxpayer > Search by GSTIN/UIN. This shows the legal and trade names, the status (Active, Cancelled, Suspended), the registration date, the constitution and the taxpayer type (regular or composition). Check that the legal name matches the purchase order.

Run the portal search when onboarding any new supplier or B2B customer, and periodically for large accounts. A cancelled supplier GSTIN means you may not be able to claim ITC on their invoices; a composition customer cannot claim ITC either.

Where must a GSTIN appear?

Your own GSTIN and, for B2B supplies, the recipient's GSTIN are mandatory on several documents. A quick reference:

Document	Your GSTIN	Customer's GSTIN
Tax invoice	Yes	Yes, if the customer is registered
Bill of supply	Yes	Yes, if registered
Credit note / debit note	Yes	Yes, if registered
Receipt voucher for advances	Yes	Yes, if registered
E-invoice (IRN)	Yes	Yes — the IRP validates it
E-way bill	Yes	Yes, or "URP" for an unregistered recipient
Signboard at place of business	Yes (displayed)	—

On a B2C invoice to a consumer there is no customer GSTIN; the place of supply and, where required, the customer's address are recorded instead. If a business buyer forgets to give you its GSTIN, the sale is treated as B2C in your GSTR-1 and the buyer cannot claim credit until you amend it — ask for the GSTIN at the quotation stage.

How is the GSTIN different from PAN, TAN and UIN?

Number	Length	Issued by	Used for
PAN	10	Income Tax Department	Income tax identity; embedded inside the GSTIN
TAN	10	Income Tax Department	Deducting and depositing TDS under income tax
GSTIN	15	GST system	Charging and paying GST, filing GST returns
UIN	15	GST system	Notified bodies such as embassies and UN organisations to claim GST refunds

The relationship to remember: one PAN, many GSTINs. If you change your business constitution — for example, a proprietorship becomes a private limited company — the PAN changes, so a new GSTIN is needed; the old one cannot simply be amended to the new PAN.

What should you do when a GSTIN check fails?

A failed check is not always a typo. Work through these steps before you save the customer or supplier:

1. Re-read the source document. Most failures are a 0 read as O, a 1 read as I, or two characters swapped while copying from a photo or PDF.
2. Count the characters. Exactly 15, no spaces or hyphens. Strip spaces before validating.
3. Check the state code against the address. A Nashik address with a GSTIN starting 29 is either a Karnataka branch or a mistake. Ask which registration the purchase belongs to.
4. Search the GSTIN on the portal. If the status is cancelled or suspended, do not issue a B2B invoice against it without clarifying, because the buyer may not be able to claim credit.
5. Match the legal name. The name on the portal should match the name on the purchase order. If a different business appears, you have been given the wrong number.
6. Record the verification. Note the date you checked and keep a screenshot or export of the result for large accounts.

Symptom	Likely cause	Action
Check character mismatch	Typing error	Ask the customer to resend the GSTIN
Valid format, "no record found"	Number never issued, or a typo that happened to pass the checksum	Ask for the registration certificate
Status "Cancelled"	Registration cancelled	Treat as unregistered unless the customer shows a revocation
State code differs from billing address	Branch registration elsewhere	Confirm which registration should be billed

Spending two minutes on these checks at onboarding avoids credit notes, amended returns and an unhappy customer months later.

Common mistakes with GSTINs

• Typing a GSTIN by hand on each invoice. Store it once in the customer master and reuse it.
• Using the PAN where a GSTIN is needed, or vice versa.
• Assuming state from the customer's billing address. Use the GSTIN state code and the place of supply rules.
• Not re-checking status. A GSTIN that was active last year may be cancelled now.
• Lowercase letters or spaces pasted from email, which fail validation on the e-invoice portal.
• Printing a branch's GSTIN on an invoice raised from another state. Each state registration invoices its own supplies.
• Confusing a composition dealer's GSTIN with a regular one. The format is identical; only the portal search shows the taxpayer type.

How billing software prevents GSTIN errors

Billing Software by Betterwork validates the format and check character when you add a customer, derives the state from the first two digits to suggest CGST+SGST or IGST, and carries the GSTIN into e-invoices, e-way bills and GSTR-1 exports so it is typed only once.

Key takeaways

• A GSTIN has 15 characters: state code (2), PAN (10), entity number (1), "Z" (1) and check character (1).
• The state code tells you where the registration is held; one PAN has a separate GSTIN in each state.
• Position 6 of the GSTIN is the PAN holder-type letter (P, F, C, H, T…).
• A checksum validator catches typos instantly, but only a portal search confirms the registration is active.
• Wrong customer GSTINs cost your customer their input tax credit — validate at entry, not at return time.

This guide is general information, not tax advice. Rules last checked on 20 October 2026; confirm with your tax professional for your situation.