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understanding credit card number sequences

10/21/2012

6 Comments

 
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From the site makeuseof.com

Tip of the Day: Unfortunately, social security numbers aren't random either -- existing numbers can be somewhat predictable. However, the US Social Security Administration started assigning random numbers in June. Remember that SSNs aren't meant to be used for identification -- you're generally not obligated to provide your SSN if you're asked for it by a business

Credit Card Numbers Are Not Random: How To Read & Understand Them Yourself by Angela Alcorn

You may have heard before that credit card numbers follow a certain pattern and structure so that they can be validated before a transaction is accepted. However, it's one thing to know that the structure is there and another thing entirely to understand how credit card numbers work.

Why would this knowledge be useful? Well, if you run a small business that doesn't process credit card payments immediately, you could save yourself money by ensuring the card details are valid. If you don't, well it could still be fun to show off your skills at parties. Here's how you do it.

Learning Where The Numbers Come From Credit card numbers are not random. There's a special set of numbers to show information about the card issuer and another set to show information about the card holder. One other number is also important, but we'll come to that later.

The very first number is the Major Industry Identifier (MII) and it tells you what sort of institution issued the card.

  • 1 and 2 are issued by airlines.
  • 3 is issued by travel and entertainment.
  • 4 and 5 are issued by banking and financial institutions.
  • 6 is issued by merchandising and banking.
  • 7 is issued by petroleum companies.
  • 8 is issued by telecommunications companies.
  • 9 is issued by national assignment.
The first six digits are the Issuer Identification Number (IIN). These can be used to look up where the card originated from. If you have access to a list that details who owns each IIN, such as this list of popular IINs on Wikipedia, you can see who issued the card just by reading the card number.

Here's a few you might recognise:

  • Visa: 4*****
  • American Express (AMEX): 34**** or 37****
  • Diner's Club International: 36****
  • Mastercard: 51**** to 55****
The seventh digit to the second-to-last digit is the customer account number. Most companies use just 9 digits for the account numbers, but it's possible to use up to 12. This means that using the current algorithm for credit cards, the world can issue about a trillion cards before needing to change the system.



We often see 16-digit credit card numbers today, but it's possible for a card issuer to issue a card with up to 19 digits using the current system. In the future, we may see longer numbers becoming more common.

The very last digit of each credit card is the check digit, or checksum. It is used to validate the credit card number using the Luhn algorithm, which we will now explain in detail.

The Luhn Algorithm Validation Check The Luhn Algorithm is used to validate all sorts of numbers, including credit cards, IMEI numbers and some social security numbers. It's not designed to be a cryptographically secure hash function, but merely a way to check errors are not made when recording numbers. It is not foolproof, but is generally considered to be useful.

Take the credit card number and read the digits from the right. Double every other number and write them down - if you do it in the same order as your card is written it will help with clarity. Now, wherever you have calculated a double-digit number, change it so that it reads as "first digit + second digit" (in other words, sum the digits of the products). Finally, take your calculations and add those numbers to the numbers remaining on your card that you didn't double. A legitimate credit card number will give you a result that is divisible by 10.

For instance, let's use a number I've just made up: 4634 8932 1298 2767. I'll enter it into a table to make it easier to understand the steps.

Try it yourself using the card from the picture earlier in this article. What can you learn from it?

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6 Comments
Credit Repair Services link
9/13/2013 08:44:12 pm

This was a nice post and I think it is pretty easy to see from the other comments as well that this post is well written and informative. Keep up the good work.

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Hhgregg link
11/11/2013 07:21:30 pm

At the same time need to see which is the best credit card for us

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mobile payments link
4/3/2014 08:37:54 pm

I was looking for the matter you shared through journal. it's quite fascinating and clearly terribly informative on behalf of me. For the buyer facing business owner, it's vital to grasp that master card transactions are returning from legitimate establishments.

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credit card debt relief link
5/29/2020 10:37:51 am

I speak from bitter experience when I write this article, as I had to claw my way out to get out of card debt in the past. What I want to make clear is that it does not matter how much you have to repay, you must realise that there is a way to get out of credit card debt.

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Heather link
1/2/2021 12:12:05 am

Great reading yourr blog

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