# Weird & Wonderful random maths fact 👀 💳

There are 4 simple steps that anyone can take to check if a credit card number is real! 💳

Credit cards have 16 numbers. The first 15 are decided by the bank but the last number uses a mathematical algorithm based on the other numbers. This “check digit” is used to check a credit card number is correct and that no errors have been made. ✅

Follow the steps below with your credit card number to check this works! 🤗

1. Beginning with the check digit (last digit), double every 2nd number (i.e. double the number to the left of the check digit and every other number after that, working from right to left)

2. If any of the answers to the above gives a 2 digit number then add these 2 numbers together (i.e. 14 ➡️ 1+4=5)

3. Add up all these values plus the digits of the credit card number that were not doubled to get one number.

4. Adding the value of the check digit to this number should give a value that is divisible by 10! So if you didn’t already know your check number then you can find it by working out the 1 digit number you would need to add to your answer to give a multiple of 10! 👀🙌🏻 (i.e. if your answer is 46 then your check digit should be 4!)

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