GSTIN verification has two parts: a format check, which catches a mistyped GST number in seconds, and a status check on the GST portal, which confirms the registration exists and is active. This guide shows how to verify a GST number end to end, how the check character in the GSTIN format is worked out, and what to look at before you pay a supplier or claim input tax credit. The portal's Search Taxpayer page needs no login, only the GSTIN and a captcha.
How to verify a GST number in two steps
First run the GSTIN through the validator above to confirm the state code, PAN and check character. Then search it on the GST portal under Search Taxpayer, which works without login and shows the registration status, legal name, trade name and effective date of registration.
- Check the format above. If the check character fails, ask the supplier to resend the number before going further.
- On the GST portal, open Search Taxpayer, choose search by GSTIN/UIN, enter the number and the captcha, and click Search.
- Compare the legal name, trade name and principal place of business with the invoice or quote.
- Click Show Filing Table, pick the financial year and see which returns the supplier has filed. Show Return Filing Frequency tells you whether it files monthly or quarterly.
If you log in first, the same search also shows a GST compliance rating from 0 to 10, whether the taxpayer is Aadhaar authenticated, its annual aggregate turnover and the share of tax it pays in cash (GST portal manual: Search Taxpayer).
GSTIN format: how is the check character calculated?
The 15th character of a GSTIN is a check character worked out from the first 14 with a mod-36 method. Each character gets a value from 0 to 35, alternate characters are doubled, and the total fixes the last character. No official specification is published, but this method matches every GSTIN printed in the CBIC notifications we tested.
- Give each character a value: digits keep their value, A is 10, B is 11, and so on up to Z at 35.
- Multiply the 1st, 3rd, 5th and other odd-position characters by 1, and the even-position characters by 2.
- If a product is 36 or more, replace it with the quotient plus the remainder after dividing by 36. For Z in 14th place, 35 × 2 = 70 becomes 1 + 34 = 35.
- Add the 14 results, divide by 36 and subtract the remainder from 36. The answer, on the same 0 to Z scale, is the check character (36 counts as 0).
Example. Take the first 14 characters of a made-up GSTIN, 27AAACB1234C1Z. The adjusted values are 2, 14, 10, 20, 10, 24, 11, 2, 2, 6, 4, 24, 1 and 35, which add up to 165. 165 divided by 36 leaves 21, and 36 minus 21 is 15, which is F. The full example GSTIN is 27AAACB1234C1ZF, and the validator above shows "Matches" for it.
What a valid GSTIN format does not prove
A GSTIN that passes the format check is only well formed. With this method, any single mistyped character always changes the expected check character, and more than 99% of swapped neighbouring characters are caught too. The check cannot tell whether the number was ever issued, is still active, or belongs to the business named on the invoice.
That is why the second step matters. Only the portal confirms that a GSTIN was issued and shows its status and any cancellation date. The PAN inside the GSTIN also gives you a quick sense check: its 4th letter shows the type of holder, and its 5th letter is the first letter of the holder's name, or of the surname for an individual (Income Tax Department).
Watch out. An invoice from a made-up "Bluepeak Foods Private Limited" quoting 27AAACB1234C1ZF fits: C for company, B for Bluepeak. If the same invoice quoted a GSTIN whose PAN has P as the 4th letter, which means an individual, the number probably belongs to someone else. Check before you pay.
What should you check before claiming input tax credit?
Input tax credit depends on the supplier, not just the number. You need a tax invoice from a supplier registered under the CGST Act (section 16(2)(a)), and since 1 January 2022 the invoice must appear in your FORM GSTR-2B after the supplier reports it in GSTR-1 or the invoice furnishing facility (rule 36(4)).
- Confirm the status is active and the effective date of registration is on or before the invoice date.
- Use the filing table to see that the supplier is filing GSTR-1. Monthly filers are due by the 11th of the next month, and quarterly filers by the 13th after the quarter (see the GST return due date calendar).
- Check your own GSTIN on every purchase invoice. Rule 46 requires a registered buyer's GSTIN on the tax invoice, and an invoice reported against a wrong GSTIN will not reach your GSTR-2B.
- Re-check vendors periodically, not only at onboarding. The bulk mode above takes up to 200 GSTINs at a time.
For a company supplier, the CIN and LLPIN lookup helps confirm that the legal name on the GST portal matches the company's MCA record.
When does a GSTIN change?
A GSTIN is tied to a PAN and a state. A business gets a new GSTIN for each state it registers in, for each extra registration in the same state, and when a change in constitution changes its PAN. A change of name, address, partners or directors keeps the same GSTIN.
| Event | Effect on the GSTIN | Rule |
|---|---|---|
| Starts supplying from Karnataka as well | New GSTIN with code 29, for example 29AAACB1234C1ZB | Section 25(1) |
| Takes a separate registration for a second place of business in Maharashtra | New GSTIN with entity character 2, for example 27AAACB1234C2ZE | Section 25(2) |
| A proprietorship becomes a company, so the PAN changes | Fresh registration in FORM GST REG-01 and a new GSTIN | Rule 19(1), proviso (d) |
| Change of legal name, address, partners or directors | Same GSTIN; apply in FORM GST REG-14 within 15 days of the change | Rule 19(1) |
All GSTINs in this table are made-up examples based on the same example PAN.
GSTIN, TRN, ARN and UIN: which number is which?
Only the GSTIN is a registration number. The TRN is a temporary reference used while you complete the application, the ARN is the application reference you use to track it after submitting Part B, and a UIN is issued to bodies such as UN agencies and embassies instead of a GSTIN.
- TRN. Generated once your PAN, mobile number and email are verified in Part A of FORM GST REG-01 (rule 8(3)). You log in with it to finish Part B.
- ARN. Lets you track the application once Part B is submitted. Statuses include Pending for Processing, Pending for Clarification, Approved and Rejected.
- GSTIN. The 15-character number on your certificate in FORM GST REG-06.
- UIN. For UN bodies, embassies, government offices and other notified persons. The same Search Taxpayer page accepts it.
Some GST TDS registrations are based on a TAN instead of a PAN (section 25(6) proviso; rule 10(1)(b)). In such a number, characters 3 to 12 follow the TAN pattern instead, and the validator labels them as a TAN rather than rejecting them. Confirm such numbers on the GST portal.
Common mistakes when you check a GST number
Most errors come from misread characters or from treating a format check as proof that a supplier is genuine. A format check is a filter; the portal search is the confirmation.
- Reading the letter O for zero or I for one. In 27AAACB1234CIZF, with the letter I as the 13th character, the entity character still looks valid, but the expected check character becomes Y, so the validator flags it.
- Matching only the trade name. The legal name is the one tied to the PAN.
- Checking a vendor once and never again.
- Ignoring the state code. A supplier billing from Pune should normally quote a GSTIN starting with 27; another code is worth a question.
If you sell goods or issue B2B invoices at scale, see whether the e-invoice and e-way bill checker applies to you as well.
How Ofin Legal can help
If you need your own GSTIN, Ofin Legal files GST registration from ₹1,499, and the GST registration checker tells you whether you must register. Our professional accounting team can also take over your GST return filing, including matching purchase invoices with GSTR-2B.
