# Why every Visa card number starts with 4

URL: https://www.paydude.io/resources/why-card-numbers-start-with-4
Type: Guide
Published: 2026-09-06 · Updated: 2026-09-06
Summary: The first digit of a card number is an industry identifier, the first six or eight are the issuer, and the last is a checksum. What each part means.

**A card number is a structured identifier, not a random string.** The first digit says which industry issued it, the first six or eight say which institution, the last is a checksum — and only the digits in between are actually your account.

## Summary

The first digit is the Major Industry Identifier: 4 and 5 are banking. The first six to eight digits identify the issuing institution. The final digit is a Luhn checksum, not account data. This is why a checkout form knows your card brand before you finish typing.

## What each part means

**A 16-digit card number, by section**

| Digits | Name | What it identifies |
| --- | --- | --- |
| 1 | Major Industry Identifier | The sector — 4 and 5 are banking and finance |
| 1–6 (or 1–8) | Issuer Identification Number | The specific bank or issuer |
| 7 to 15 | Account identifier | The cardholder's account at that issuer |
| 16 | Check digit | A Luhn checksum over everything before it |

## Who has which prefix

**Network prefixes**

| Network | Starts with | Typical length |
| --- | --- | --- |
| Visa | 4 | 16 |
| Mastercard | 51–55, and part of the 2 range | 16 |
| American Express | 34, 37 | 15 |
| Discover | 6011, 64, 65 | 16 |
| Diners Club | 36, 38 | 14 |

American Express is the visible oddity: 15 digits rather than 16, a legacy of having built its own system rather than adopting the bank-card conventions. It is also why some checkout forms handle Amex badly — a hard-coded 16-digit assumption breaks on it.

## What the BIN reveals

Because the first six to eight digits identify the issuer, they also reveal a good deal about the card without contacting anyone.

- **The network**, which is why the correct logo appears as you type.
- **The issuing bank**, and therefore usually the country of issue.
- **The card type** — debit, credit, prepaid, corporate — which determines what it costs to accept.
- **Whether a surcharge applies**, since international and commercial cards are priced differently.

> **Six digits is no longer enough:** The six-digit identifier space was running out, so the networks moved to eight-digit IINs. Any system that assumed six — and many did, for decades — has had to be updated to avoid misidentifying newer cards.

## Why this matters to a merchant

BIN lookup is how a processor knows, before authorization, whether a transaction will attract an international or commercial-card surcharge. It is the mechanism behind the situational fees on every rate card — including [ours](https://www.paydude.io/pricing).

It is also how fraud systems flag geographic mismatches, and how a checkout can decide whether to trigger [3D Secure](https://www.paydude.io/resources/what-is-3d-secure).

## Sources

- ISO/IEC 7812 — identification cards, identification of issuers.
- Published network BIN ranges from Visa, Mastercard, American Express and Discover.
- Card network guidance on the migration from six-digit to eight-digit issuer identifiers.

**Situational fees, published up front** Including exactly what international and commercial cards cost. — [See the rate card](https://www.paydude.io/pricing)

## Frequently asked questions

### Why do Visa cards start with 4?

Because 4 is Visa's assigned Issuer Identification Number range under ISO/IEC 7812. The first digit is the Major Industry Identifier, and both 4 and 5 are allocated to banking and finance. Mastercard uses 5 (and part of the 2 range), American Express 34 and 37, Discover 6011 and others.

### What is a BIN or IIN?

The first six — increasingly eight — digits of a card number, identifying the institution that issued it. BIN stands for Bank Identification Number and IIN for Issuer Identification Number; IIN is the current standard term for the same thing.

### Can you tell anything about a card from its number?

The network, the issuing bank, and usually the card type and country. That is why checkout forms display the right card logo as you type, and why fraud systems can flag a card issued in one country being used in another.

### Why did BINs expand from six digits to eight?

The six-digit space was running out. The card networks moved to eight-digit identifiers to create more room for issuers, which is why systems that hard-coded a six-digit assumption have had to be updated.