A GST number (GSTIN) is always exactly 15 characters, in a fixed format: a 2-digit state code, followed by 10 characters that are the business's PAN, followed by 3 more characters that identify the specific registration. Here's exactly how to read one, with a worked example.

The 15-character structure

Every GSTIN follows the same layout, in this order:

Position	Length	What it represents
1–2	2 digits	State code (where the business is registered)
3–12	10 characters	The business's PAN (Permanent Account Number) — identical to their income tax PAN
13	1 character	Entity number — which registration this is if the same PAN has multiple GST registrations in one state (usually "1")
14	1 character	Always the letter "Z" by default
15	1 character	Checksum digit — calculated from the other 14 characters, used to detect typos

Worked example

29ABCDE1234F1Z5 breaks down as:
• 29 — Karnataka
• ABCDE1234F — the business's PAN
• 1 — first GST registration for this PAN in this state
• Z — fixed default character
• 5 — checksum digit

This is an illustrative example only — it is not a real, active GSTIN.

State codes (most common)

The first two digits tell you which state the GSTIN was issued in — useful for spotting whether a client's GSTIN matches the state they claim to operate from, and for figuring out CGST/SGST vs IGST when you're invoicing:

Code	State
01	Jammu & Kashmir
02	Himachal Pradesh
03	Punjab
05	Uttarakhand
06	Haryana
07	Delhi
08	Rajasthan
09	Uttar Pradesh
10	Bihar
19	West Bengal
21	Odisha
22	Chhattisgarh
23	Madhya Pradesh
24	Gujarat
27	Maharashtra
29	Karnataka
32	Kerala
33	Tamil Nadu
36	Telangana
37	Andhra Pradesh

Full list of all 37 state/UT codes is published on the official GST portal — the table above covers the states most freelancers and agencies invoice most often.

How to tell if a GSTIN is valid (without calling the government)

It must be exactly 15 characters — anything shorter or longer is invalid
Characters 3–12 (the PAN portion) must follow standard PAN format: 5 letters, 4 digits, 1 letter
The 14th character is always "Z"
The first 2 digits must be a real, currently-used state code (01–37, with a few gaps)
The last character is a checksum calculated from the previous 14 — if it doesn't match, the number is either mistyped or fabricated

If you want to confirm a GSTIN is actually active and registered (not just correctly formatted), the only reliable way is the "Search Taxpayer" tool on the official GST portal — format validity and active-registration status are two different checks.

"Dummy" and "sample" GST numbers — what people actually need

A lot of searches for "dummy GST number" or "sample GST number" come from developers and freelancers testing an invoice template, a form, or a piece of software that validates GSTIN format — not from anyone trying to file with a fake number (which isn't legal). If that's you, the safest approach is:

Use a number that matches the format (15 characters, correct structure) but is clearly not a real business's registration — most developers use a well-known placeholder pattern for this.
Never submit a fabricated GSTIN in an actual invoice, GST return, or e-way bill — using one that isn't genuinely registered is a compliance problem, not a shortcut.
If you're testing your own software, check whether your GST software provider offers a proper sandbox/test mode instead of using a placeholder number in a live system.

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Why the format matters for your invoices

Beyond satisfying curiosity, the GSTIN format directly affects how you invoice: the state code in your client's GSTIN (not their billing address) determines whether you charge CGST+SGST or IGST. Two clients in the same city can have GSTINs registered in different states if their registered office differs from where you're actually doing the work — always go by the GSTIN's state code, not assumptions.

Frequently Asked Questions

How many characters does a GST number have?

Always exactly 15 — 2 digits for the state code, 10 characters for the PAN, 1 entity code, the fixed letter "Z", and 1 checksum digit.

What do the first two digits of a GSTIN mean?

They're the state code showing which state the GST registration was issued in — for example, 07 is Delhi, 27 is Maharashtra, 29 is Karnataka.

Is the PAN inside a GST number the same as the income tax PAN?

Yes — characters 3 through 12 of every GSTIN are exactly the business or individual's 10-character income tax PAN.

Can I use a dummy GST number for testing an invoice template?

For checking that a template displays and formats correctly, using a clearly fake, correctly-structured placeholder is common practice among developers. Never use a fabricated number on an actual invoice, GST return, or any document submitted for real compliance purposes.

How do I check if a GSTIN is actually real and active, not just correctly formatted?

Format validation (the checks in this guide) only confirms the structure is correct. To confirm a GSTIN is genuinely registered and active, use the "Search Taxpayer" tool on the official GST portal (gst.gov.in).

GST Number Format Explained: How to Read a GSTIN (With Examples)