Everybody have at least a credit card in their wallet. We know for sure that this card is useful. But how much do we know about these cards.

Here is a little trick about how the numbers are generated and how to validate a credit card.

Let’s get started.

### Major Industry Identifier

The first digit is the Major Industry Identifier.It designates the category of the entity which issued the card.

**1 and 2 are airlines**

**3 is Travel and entertainment.**

**4 and 5 are banking and financial**

**7 is petroleum**

**8 is telecomunications**

**9 is national assignment.**

### Issuer Identification Number(IIN)

The first 6 digits are Issuer Identification Number. It will identify the institution that issued the card.

**Visa 4xxxxx**

**Mastercard 51xxxx – 55xxxx**

**Discover 6011xx, 644xxx and 65xxxx**

**Amex 34xxxx and 37xxxx**

Cards can be looked up by their IIN. A card that starts with 37621 is a Singapore airlines krisflyer American express gold card. 529962 designates a prepaid Much music mastercard.

### Person’s account number

The 7th and following digits , excluding the final digits are the person’s account number. This leaves a trillion possibilities if the maximum of 12 digits is used. Most cards use just 9 digits.

### Checksum

The final digit is the check digit or checksum. It is used to validate the credit card number using the Luhn algorithm.

### How to validate a credit card.

Lets take the above credit number for example:

**7 2 5 3 3 2 5 6 7 8 9 5 1 2 4 5**

And double every other digit from the right

*(7×2)* 14 *(5×2)* 10 *(3×2)* 6 *(5×2)* 10 *(7×2)* 14 *(9×2)* 18 *(1×2)* 2 and finally *(4×2)* 8

Add these new digits to undoubled ones

**2 3 2 6 8 5 2 5**

All double digits are added as a sum of their digits for example 14 = 1 + 4

**1+4+2+1+0+3+6+2+1+0+6+1+4+8+1+8+5+2+2+8+5**

**It gives a total of 124**

A credit card number is valid only when the final sum is divisable by 10. In the case of our example, it is a fake credit card number or an invalid one.

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