What Is A Credit Card Number?

You probably get asked for the credit card number whenever you make a purchase online and you can see the long string of numbers printed on the front of your card, but you may wonder what is the credit card number and what do the numbers in it mean.

The credit card number is the long number on the front of your credit card that is typically between 14 and 16 digits long and serves as the identifier for your credit card account to make transactions, payments or interact with your credit card company.

Read on to find out exactly what the credit card number is, interesting information about it and things you may not know about the format.

What do the numbers on a credit card mean?

The long credit card number on the front of your card is actually composed of a few different sections which have their own specific meaning.

The first two characters on the card are used to identify the Issuing Network - the vast majority of credit cards will be a Visa, Mastercard or American Express and you may have heard of other issuing networks such as Discover or Diners Club although these are much more rare.

Visa and Mastercard use their networks for both credit cards and debit cards using the same first numbers while American express only issues credit cards and schemes like Maestro are exclusive to debit and prepaid cards.

If you look at the long number on the front of your card, you'll most probably notice that the first two digits are one of the following:

Issuing NetworkFirst two digitsLength of credit card number
American Express34, 3715
Diners Club30, 36, 38, 39, 54, 5514 except U.S. where it's 16
Mastercard22-27 and 51 - 5516
Visa41 to 4916

The next 4 digits of a credit card number are usually the numbers that identify the bank or Financial Services company that has issued your credit card.

Together with the first 2 digits, the first 6 digits are known in the industry as the Bank Identification Number or the BIN.

The rest of the credit card number is assigned by your credit card company to identify your account. Some banks use the first two of these digits (i.e. digits 7 and 8 from the overall number) to identify different internal products, countries or regions, but there is no standard way that these numbers are structured.

Why are credit card numbers different lengths?

Most credit card numbers have 16 digits. You'll recognise these neatly arranged in 4 groups of 4 on the front of your card and if your card is Visa or Mastercard, this is what you'll be used to.

Some find it surprising to find out that not all credit cards have 16 digits. There is no set agreed number and the range is from 12 to 19.

If you look at the front of an American Express card, for example, you'll notice that their card number have only 15 digits - these are shown as groups of 4, 6 and 5.

If you've ever seen a Diners Club card, they have just 14 digits in the UK (but 16 in the US and Canada).

No major UK credit card companies offer cards with more than 16 digits although some rare business cards do as do some old style Maestro debit cards.

The choice of how many numbers to use is generally up to each Issuing Network. 16 seems to be an agreed optimal compromise between having as many possible card number options and still making it easy for customers to use.

As most payment processors and card payment terminals work with multiple different schemes, it's a bad idea to do something that is very different to the established networks as it will make it harder for all of those terminals to work with you as well.

Diners Club was the company that first invented credit cards so they originally went for shorter numbers as they didn't necessarily anticipate the entire world adopting to their system a few decades later.

Are the three digits on the back part of the credit card number?

All credit cards have an additional few numbers that are there for security when making payments.

The CVV number on the back of a credit card is not part of the credit card number.
The CVV number on the back of a credit card is not part of the credit card number.

These are often called CVV or CVC numbers and are usually found on the back of the card. Sometimes the last few digits of the number from the front is printed in front of the 3 additional digits making it even more confusing.

To make things even more difficult, American Express have a 4-digit equivalent and instead of printing it on the back they stick it right on the front of the card - usually in the top right hand corner.

Al though these numbers are often called "the last 3 digits", they are in fact not part of the credit card number. They exist simply as an additional code that is used to process transactions where the cardholder is not present.

The reason why this system exists is because these additional digits are the only part of the information on the card that is not coded into the chip or the magnetic stripe on the back. This means that even if somebody steals all the information from your card, they won't have those extra digits and they won't be able to make payments online or remotely.

Are credit card numbers randomly assigned?

When looking at the long card number, you might wonder whether a computer randomly comes up with these numbers to print onto the card when you first apply or get a card reissued. Is there any logic to it?

The answer is yes - there's more to it than you might think!

In general, other than the BIN number at the front of the card, each bank or credit card company has the flexibility to decide how to produce credit card numbers.

In many cases the first 2 digits of the remaining credit card number are used to group customers by region, product type or an internal record system. The rest of the numbers are usually assigned one of two ways: sequentially or randomly generated.

Random number generation is much more secure and produces a number that doesn't tell you much about anything. It is operationally slightly more difficult because you have to have good enough systems to check and prevent you issuing the same card number twice.

Some providers opt for sequential numbering - you'll know if your credit card is using sequential numbers if you see a load of zeros in the middle of your card starting from the 7th or 9th digit.

Sequential numbering is a really poor way of assigning numbers. In 2016 Tesco Bank was in the news for losing over £2 million because hackers figured out that all of their credit card numbers were sequential which meant the expiry dates would also match on sequential cards (seeing as they must have been printed a few seconds apart).

Even so, some credit card companies including MBNA still issue sequentially numbered cards.

The Luhn Checksum formula for credit card numbers

There is one other little known secret to how credit card numbers are generated. Virtually all credit card numbers follow the Luhn Checksum formula to help avoid customers accidentally mistyping their number when ordering items online.

The formula is simple - start from the back of the card number and do the following:

Take every 2nd number and multiply it by 2. If the new number is greater than 9, add the two digits of the new number to make the new number.

So if you use 8 as an example, then doubling it gets you 16 and you then add 1 and 6 to make 7.

After you've gone and doubled every other number, write out the new "doubled" card number down - write all the odd numbers as they are and the even numbers in the doubled format as above starting from the right.

Now add all of the numbers together. Valid credit card numbers always have the sum as a multiple of 10! Try it on your own credit card!

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