What Is a BIN (Bank Identification Number)? The Complete Guide

Every credit card number tells a story before you even get to the account digits. The first six to eight numbers — known as the BIN (Bank Identification Number) — reveal the card network, the issuing bank, the card type, and even the country of origin.

If you've ever wondered why a Visa card always starts with a 4, or how payment processors instantly know which bank issued a card, the answer is the BIN.

This guide breaks down everything: what BINs are, how they work, why the industry is shifting to 8-digit IINs, and how you can look up any BIN instantly using our free BIN Checker tool.

What Is a BIN (Bank Identification Number)?

A BIN, or Bank Identification Number, is the first six to eight digits of a credit card, debit card, or prepaid card number. These digits identify the institution that issued the card.

When you swipe, tap, or type your card number into a payment form, the BIN is the very first thing the system reads. It tells the payment processor:

• Which card network handles the transaction (Visa, Mastercard, American Express, etc.)
• Which bank or financial institution issued the card
• What type of card it is (credit, debit, prepaid, corporate)
• Which country the card was issued in

Think of it as the card's ID badge. Before the merchant's payment system even checks whether you have enough money, it uses the BIN to route the transaction to the right network and the right bank.

A Quick Example

Take this card number: 4532 0151 2345 6789

The first six digits (453201) are the BIN. With just those six numbers, a BIN lookup reveals: Visa network, credit card, issued by a specific bank in a specific country.

Want to try it? Paste any BIN into the Namso BIN Checker to see the full breakdown — network, issuer, type, and country — in seconds.

BIN vs. IIN: What's the Difference?

You'll see both terms used interchangeably, but there's a technical distinction:

• BIN (Bank Identification Number): The original term — refers to the first 6 digits of a card number. Defined under ISO/IEC 7812.
• IIN (Issuer Identification Number): The updated, official term. Same standard (ISO/IEC 7812), but renamed because not all card issuers are banks. Think fintechs, prepaid card companies, and corporate expense platforms.

The Shift to 8-Digit IINs

Historically, BINs were 6 digits long. That gave the industry roughly 1 million possible BIN combinations — which seemed plenty when the system was designed decades ago.

But the explosion of new card issuers — neobanks, fintechs, buy-now-pay-later providers, virtual card platforms — created a BIN shortage. The industry was literally running out of unique 6-digit prefixes.

Solution: In April 2022, the major card networks began the transition to 8-digit BINs (officially called IINs). This expands the available combinations from 1 million to 100 million — enough to handle decades of growth.

In practice: Most people (and most systems) still say "BIN." Old and new formats coexist. If you're working with payment processing, be prepared to handle both 6-digit and 8-digit identifiers.

Note: The total card number length (typically 16 digits for Visa/Mastercard) stays the same. The 8-digit IIN just means more of those digits are allocated to identifying the issuer, and fewer to the account number.

How BIN Numbers Are Structured

Every card number follows a specific anatomy. Let's break it down digit by digit.

The MII (Major Industry Identifier)

The very first digit of any card number is the MII — it identifies the industry category of the issuer.

This is why a Visa card always starts with 4 and an Amex always starts with 3 (specifically 34 or 37). The MII is baked into the card's DNA.

Full BIN Structure

After the MII, the remaining BIN digits narrow down the specific issuer:

Card Number:  4  5  3  2  0  1  5  1  2  3  4  5  6  7  8  9
              ├─────────────────┤  ├──────────────────┤  ├──┤
              BIN / IIN (6-8)      Account Number        Check
              (Issuer ID)          (Unique to holder)    Digit

• Digits 1–6 (or 1–8): The BIN/IIN — identifies network + issuer + card type + country
• Digits 7–15 (or 9–15): Account number — unique to each cardholder
• Digit 16: Check digit — calculated using the Luhn algorithm to catch typos and errors

Common BIN Ranges by Card Network

Here's a quick reference of BIN prefixes for the major card networks:

Visa

Visa has the widest BIN allocation — the entire 4xxx range gives them approximately 100,000 possible 6-digit BINs.

Mastercard

Mastercard uniquely spans two MII ranges (2 and 5), which is unusual and was done to accommodate growing demand.

American Express

Amex cards are 15 digits (not 16), and the BIN structure is tighter — only two 2-digit prefixes for the entire network.

Discover

Other Networks

Pro tip: Use the Namso BIN Checker to look up any specific BIN and see the exact network, issuer bank, card type, and country.

How to Look Up a BIN

There are two common approaches:

1. Use a BIN Checker Tool

The fastest method. Enter the first 6–8 digits of any card number into a BIN lookup tool and get instant results:

• Card network (Visa, Mastercard, Amex, etc.)
• Issuing bank name
• Card type (credit, debit, prepaid)
• Card level (classic, gold, platinum, corporate)
• Country of issue with flag
• Currency associated with the issuer

The Namso BIN Checker provides all of this for free, with no registration required.

2. BIN Database / API Lookup

For developers and businesses processing payments at scale, BIN databases offer programmatic access:

• BIN list databases — downloadable CSV/JSON files with millions of BIN entries
• BIN APIs — real-time lookup endpoints for payment systems
• ISO 8583 standards — the messaging format that transmits BIN data between payment processors

Most commercial payment processors (Stripe, Adyen, Braintree) perform BIN lookups internally as part of transaction routing. But if you're building your own payment system or doing fraud analysis, you'll want direct BIN database access.

BINs in Payment Processing

When you use your card at a store or online, the BIN kicks off a chain reaction that happens in milliseconds:

The Transaction Flow

1. You tap/swipe/enter your card number
2. Merchant's POS or payment gateway reads the BIN (first 6–8 digits)
3. BIN lookup identifies the card network → Transaction routes to Visa, Mastercard, etc.
4. Card network identifies the issuing bank → Transaction forwarded to your bank
5. Issuing bank checks your account → Sufficient funds? Credit limit? Fraud flags?
6. Authorization response sent back → Approved or declined, within ~2 seconds

The BIN is what makes step 2–4 possible. Without it, the payment system wouldn't know where to send the transaction.

Why BINs Matter for Merchants

Merchants and payment processors use BIN data for:

BINs in Fraud Prevention

BINs are a first line of defense in payment fraud detection. Here's how:

Common BIN-Based Fraud Checks

BIN Velocity Attacks

A common fraud pattern called BIN attack (or card testing) works like this:

1. Fraudster obtains a valid BIN (e.g., from a stolen card)
2. Generates thousands of card numbers using that BIN + random account numbers
3. Tests them against small-value transactions to find valid combinations
4. Uses valid cards for larger purchases

Payment processors detect this by monitoring transaction velocity per BIN range. When they see an unusual spike of attempted transactions from the same BIN, they flag and block them.

For developers: When testing payment systems, use Namso Gen to generate valid test card numbers instead of using real card ranges. Test cards pass Luhn validation but are flagged as test cards by payment gateways, keeping your testing safe and compliant.

BIN Ranges and Card Levels

BINs don't just identify the network and bank — they also encode the card level:

Merchants pay different interchange fees depending on the card level. A transaction on a Visa Signature card costs the merchant more in processing fees than the same amount on a Visa Classic debit card. BIN lookup reveals the card level, which helps merchants forecast processing costs.

Testing with BINs: How Namso Gen Helps

If you're a developer testing payment integrations, you need card numbers that:

• ✅ Pass Luhn algorithm validation
• ✅ Match real BIN patterns (so your system processes them correctly)
• ✅ Are recognized as test cards (so no real money moves)

Namso Gen lets you generate card numbers based on specific BINs. Enter a BIN, and the tool produces valid test card numbers that match that BIN's network, type, and format. This is invaluable for:

• Payment form validation — Does your checkout accept the card formats your users carry?
• Gateway integration testing — Does your system correctly route transactions for different networks?
• BIN-based logic testing — Does your fraud detection flag the right card types?
• Localization testing — Do country-specific card formats work correctly?

For gateway-specific test cards, check our complete reference guide.

Frequently Asked Questions

What does BIN stand for?

BIN stands for Bank Identification Number. It refers to the first six to eight digits of a payment card number that identify the issuing institution and card network. The more formal, updated term is IIN (Issuer Identification Number), since not all card issuers are traditional banks.

How many digits is a BIN?

Traditionally, BINs are 6 digits. However, the payment industry began transitioning to 8-digit BINs (IINs) in April 2022 to accommodate the growing number of card issuers worldwide. Both formats currently coexist.

Is a BIN the same as an IIN?

Functionally, yes. IIN (Issuer Identification Number) is the updated, official name under ISO/IEC 7812. The term "BIN" persists because it's been used for decades and most people in the industry still say BIN. The main difference is that IIN acknowledges that issuers aren't always banks.

Can I find out which bank issued a card from the BIN?

Yes. A BIN lookup reveals the issuing bank, card network, card type (credit/debit/prepaid), card level (classic/gold/platinum), and the country of issuance. Use the Namso BIN Checker to look up any BIN for free.

Is it legal to look up BIN numbers?

Yes. BIN information is not sensitive or private data. BIN databases are publicly available and widely used by merchants, payment processors, and fraud prevention systems. Looking up a BIN is standard practice in the payments industry.

Why do Visa cards always start with 4?

The first digit of a card number is the MII (Major Industry Identifier). The number 4 is assigned to the banking and financial sector, and within that range, Visa was allocated all BINs beginning with 4. Mastercard was assigned the 51–55 and 2221–2720 ranges. These allocations are governed by ISO/IEC 7812.

What is a BIN attack?

A BIN attack (also called card testing) is a fraud technique where attackers take a known valid BIN and generate thousands of possible card numbers, then test them against merchant payment systems with small transactions. Payment processors detect this through BIN velocity monitoring — watching for unusual transaction spikes from the same BIN range.

How do BINs help prevent fraud?

BINs enable multiple fraud detection checks: country mismatch detection (card issued in a different country than the billing address), card type anomalies (prepaid card used for high-value purchase), velocity monitoring (many cards from the same BIN range used rapidly), and known fraud BIN tracking (BIN ranges with high historical fraud rates).