GSTIN Format and Validation: What Each of the 15 Characters Means

Every business registered under GST in India gets a GSTIN — a 15-character Goods and Services Tax Identification Number. It appears on every tax invoice, and when you sell to another business, their GSTIN goes on your bill too. A wrong GSTIN can cost the buyer their input tax credit, so it pays to know how the number is built and how to spot a mistake.

The 15 characters at a glance

The example above is only to show the layout — it is not a real business.

1. State code (characters 1 and 2)

The first two digits show the state or union territory where the business is registered. They always have two digits, so Delhi is 07, not 7. The state code also decides how GST is charged on a sale: when the seller’s and the buyer’s state codes match, the bill shows CGST + SGST; when they differ, it shows IGST.

Code 25 (Daman and Diu) is no longer used since the 2020 merger with Dadra and Nagar Haveli, which uses 26. Code 28 belonged to Andhra Pradesh before the state was divided; Andhra Pradesh now uses 37.

2. PAN (characters 3 to 12)

The next ten characters are the PAN of the business or proprietor. A PAN always has five letters, four digits and one letter — for example ABCDE1234F. So characters 3–7 must be letters, 8–11 digits and 12 a letter. If that pattern breaks, the GSTIN is wrong.

3. Entity number (character 13)

One PAN can hold more than one GST registration in the same state — for example, two business verticals. The 13th character counts them: 1 for the first registration, 2 for the second, and after 9 it continues with letters A to Z.

4. The letter Z (character 14)

For regular taxpayers the 14th character is Z. If you see anything else in this position on an ordinary business’s GSTIN, check the number again.

5. Check character (character 15)

The last character is calculated from the first 14 using a fixed formula, so it catches most typing mistakes — a swapped digit or a wrong letter changes what the check character should be. It can be a digit or a letter.

How to check a GSTIN before you put it on a bill

1. Count the characters. It must be exactly 15, with no spaces.
2. Read the state code. Is it one of the codes in the table, and is it the state you expect for that customer or supplier?
3. Check the PAN part. Five letters, four digits, one letter.
4. Look at character 14. For a regular business it should be Z.
5. Confirm it is active. The pattern only tells you the number is well-formed. To be sure the registration is real and active, use Search Taxpayer on the official GST portal (gst.gov.in), which shows the legal name and status.

Watch out for look-alike characters when someone reads a GSTIN out over the phone: 0 and O, 1 and I, 5 and S, 8 and B.

Check a GSTIN here — free

Type or paste a GSTIN below. Our free checker tests steps 1 to 4 and the check character in one go, and shows what each part means. It only checks the format — step 5 on the GST portal is still needed.

Why it matters for your shop

• Your customers’ input tax credit. A business buyer can claim GST credit only if their correct GSTIN is on your invoice and in your GST return.
• The right tax on the bill. The state code decides CGST + SGST or IGST. Charging the wrong one means correcting the bill later.
• Clean GST returns. Wrong GSTINs on B2B bills show up as mismatches when your buyers reconcile their purchases.

How RetailCore helps

In RetailCore, a business customer’s GSTIN is saved with the customer, so you type it once and it appears on every bill to them. When the customer is from another state, RetailCore applies IGST by itself. Your own GSTIN, the state of supply and the tax breakup print on every invoice, and GSTR-1 and GSTR-3B reports are ready from the same bills.