How to Check a GST Number: Format Check vs Verifying It on the GST Portal
Before you put a customer's GSTIN on a bill, check two things: that the number is correctly formed, and that it belongs to an active registration. Here is how to do both for free, and what each check can and cannot tell you.
BillBabu Team
BillBabu App Team
In short
- A GSTIN is the 15-character GST number of a registered business: a 2-digit state code, the 10-character PAN, an entity number, the letter Z and a check digit.
- A format check catches typing mistakes in seconds, using the check digit. Try our free GSTIN format check.
- A format check cannot tell you whether the GSTIN is real or active. For that, use Search Taxpayer on the GST portal. It is free and needs no login.
- Do both before the first B2B invoice to a new customer.
Why the buyer's GSTIN matters
When you sell to a registered business, their GSTIN goes on your invoice and into your GST return. Their input tax credit depends on it: the tax you charged shows up in their records only under the GSTIN you reported. A wrong digit means the credit does not reach your customer, and you get a phone call asking you to fix your return.
A wrong state code causes a second problem. It can make you charge CGST + SGST where IGST was due, or the other way round. Checking the number once, when you add the customer, avoids both.
How a GSTIN is built
Take the sample GSTIN 27AAPFU0939F1ZV:
| Characters | Example | Meaning |
|---|---|---|
| 1 to 2 | 27 | State code (27 is Maharashtra) |
| 3 to 12 | AAPFU0939F | The PAN of the business. Its 4th letter shows the type: P for an individual, F for a firm, C for a company |
| 13 | 1 | Entity number: 1 for the first registration under this PAN in the state, then 2 to 9, then A to Z |
| 14 | Z | Z by default |
| 15 | V | Check digit, worked out from the first 14 characters |
Some common state codes: 07 Delhi, 08 Rajasthan, 09 Uttar Pradesh, 10 Bihar, 19 West Bengal, 23 Madhya Pradesh, 24 Gujarat, 27 Maharashtra, 29 Karnataka, 32 Kerala, 33 Tamil Nadu, 36 Telangana, 37 Andhra Pradesh.
Step 1: check the format
The check digit is the clever part. It is calculated from the first 14 characters, so if any one of them is mistyped, the 15th usually no longer matches. That catches most typing errors before they reach your bill.
Our free GSTIN format check does three things: it confirms the state code, checks that the middle part has the shape of a PAN, and recalculates the check digit. It runs in your browser and takes a second.
What it cannot do is tell you whether the GSTIN was ever issued, or whether it is still active. A made-up number with a correct check digit passes a format check.
Step 2: confirm it on the GST portal
- Open Search Taxpayer on the GST portal. You do not need to log in.
- Choose Search by GSTIN/UIN, type the number and the captcha, and search.
- Read the result. It shows the legal name and trade name of the business, the date of registration, the status (Active, Suspended or Cancelled), the taxpayer type (Regular or Composition) and the state.
Match the legal name with what your customer told you. If the status is not Active, or the name is different, ask before you bill. If the portal shows Composition for a supplier of yours, remember that composition dealers cannot charge GST, so their bill to you should be a bill of supply without GST.
The portal also has Search by PAN, which lists all GSTINs registered under one PAN, handy when a customer has registrations in more than one state.
Format check vs portal search
| Format check | GST portal search | |
|---|---|---|
| Catches typing mistakes | Yes | Yes (the number will not be found) |
| Shows the business name | No | Yes |
| Shows if it is active | No | Yes |
| Shows Regular or Composition | No | Yes |
| Time | A second | About a minute, with a captcha |
Worked example: two customers, two problems
Sharma Electricals in Pune adds two new business customers.
- Customer A sends 27AAPFU0939F1ZX on WhatsApp. The format check fails on the check digit: the last character should be V. A quick call confirms the customer mistyped it. The correct GSTIN goes on a ₹23,600 invoice, so ₹3,600 of GST reaches the right buyer's credit.
- Customer B's GSTIN passes the format check, but the portal shows it as Cancelled. Sharma Electricals bills them as an unregistered buyer, without a GSTIN on the invoice, and tells them why. Putting a cancelled GSTIN on the bill would not have given them any credit anyway.
Adding GSTINs in BillBabu
When you add a party in the BillBabu app, the GSTIN field guides you as you type: it expects digits where the state code goes, letters and digits where the PAN goes, and so on, and shows the format (2-digit state code, 10-character PAN, entity, Z, check digit) under the box. BillBabu also stops you from adding the same GSTIN twice in one business. The party's state then decides whether your invoices carry CGST + SGST or IGST, as explained in CGST, SGST and IGST: which one goes on your bill.
BillBabu does not look the number up on the GST portal for you, so for a new business customer, do the portal search once. After that, every invoice uses the saved GSTIN. If you are registering your own business, see our GST registration guide, and once customers are set up, keep their dues in a party ledger.
GST portal steps checked on 4 October 2026, under the GST 2.0 rates in force since 22 September 2025. Rates can depend on the exact item, its price or its packing, so confirm your item in the CBIC rate notification or with your CA.
Frequently asked questions
Can I check a GST number without logging in?
Yes. Search Taxpayer on the GST portal works without a login. You only need to type a captcha.
If a GSTIN passes the format check, is it genuine?
Not necessarily. The format check only shows that the number is correctly formed. Only the GST portal can confirm that it was issued and is active.
What does the Z in a GSTIN mean?
The 14th character is Z by default for normal registrations. It has no meaning you need to act on.
Can I find a business's GSTIN from its PAN?
Yes. On the GST portal, Search Taxpayer has a Search by PAN option that lists the GSTINs registered under that PAN.
Save each customer's GSTIN once and bill without retyping. BillBabu is a GST billing app for Android, with a web app at app.billbabu.com. Make GST invoices and estimates, share them as PDFs and see who still owes you money. Every account starts with a 14-day free trial, and you do not need a card. Get BillBabu on Google Play or see plans and prices.
Tags
Related Articles
Voluntary GST Registration: Should Small Businesses Opt In?
2 min read
Annual Aggregate Turnover Under GST: What to Include and Why It Matters
2 min read
GST Exemptions: Nil-Rated, Exempt, and Zero-Rated Supplies Explained
2 min read
GST invoicing made easy for Indian small businesses
Create GST-compliant invoices & estimates, track payments, manage parties and inventory — all from your phone. 14-day free trial, no credit card needed.