How to validate a Credit Card Number?
Most credit card number can be validated using the Luhn algorithm, which is more or a less a glorified Modulo 10 formula!
The Luhn Formula:
- Drop the last digit from the number. The last digit is what we want to check against
- Reverse the numbers
- Multiply the digits in odd positions (1, 3, 5, etc.) by 2 and subtract 9 to all any result higher than 9
- Add all the numbers together
- The check digit (the last number of the card) is the amount that you would need to add to get a multiple of 10 (Modulo 10)
Luhn Example:
| Step |
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Total |
| Original Number: |
4 |
5 |
5 |
6 |
7 |
3 |
7 |
5 |
8 |
6 |
8 |
9 |
9 |
8 |
5 |
5 |
|
| Drop the last digit: |
4 |
5 |
5 |
6 |
7 |
3 |
7 |
5 |
8 |
6 |
8 |
9 |
9 |
8 |
5 |
|
|
| Reverse the digits: |
5 |
8 |
9 |
9 |
8 |
6 |
8 |
5 |
7 |
3 |
7 |
6 |
5 |
5 |
4 |
|
|
| Multiple odd digits by 2: |
10 |
8 |
18 |
9 |
16 |
6 |
16 |
5 |
14 |
3 |
14 |
6 |
10 |
5 |
8 |
|
|
| Subtract 9 to numbers over 9: |
1 |
8 |
9 |
9 |
7 |
6 |
7 |
5 |
5 |
3 |
5 |
6 |
1 |
5 |
8 |
|
|
| Add all numbers: |
1 |
8 |
9 |
9 |
7 |
6 |
7 |
5 |
5 |
3 |
5 |
6 |
1 |
5 |
8 |
|
85 |
| Mod 10: |
85 modulo 10 = 5 (last digit of card) |
| American Express |
34, 37 |
15 |
| Diners Club - Carte Blanche |
300, 301, 302, 303, 304, 305 |
14 |
| Diners Club - International |
36 |
14 |
| Diners Club - USA & Canada |
54 |
16 |
| Discover |
6011, 622126 to 622925, 644, 645, 646, 647, 648, 649, 65 |
16 |
| InstaPayment |
637, 638, 639 |
16 |
| JCB |
3528 to 3589 |
16 |
| Laser |
6304, 6706, 6771, 6709 |
16-19 |
| Maestro |
5018, 5020, 5038, 5893, 6304, 6759, 6761, 6762, 6763 |
16-19 |
| MasterCard |
51, 52, 53, 54, 55 |
16-19 |
| Visa |
4 |
13-16 |
| Visa Electron |
4026, 417500, 4508, 4844, 4913, 4917 |
16 |
