Regular expression to match credit card expiration date

Question

I have the following pattern which I'm trying to use to match credit card expiration dates:

(0[1-9]|1[0-2])\/?(([0-9]{4})|[0-9]{2}$)

and I'm testing on the following strings:

It should only match the first four strings, and the last 3 should not be a match as they are invalid. However the current pattern is also matching the last string. What am I doing wrong?

Maybe I'm just a little confused but are you sure your parenthesis are correct around the `[0-9]{4}` area? — BlackVegetable, Dec 06 '13 at 18:00
@BlackVegetable I'm new to regex - what's the problem with the parentheses? — Snowman, Dec 06 '13 at 18:03

score 45 · Accepted Answer · answered Dec 06 '13 at 18:00

45

You're missing start of line anchor ^ and parenthesis are unmatched.

This should work:

re = /^(0[1-9]|1[0-2])\/?([0-9]{4}|[0-9]{2})$/;

OR using word boundaries:

re = /\b(0[1-9]|1[0-2])\/?([0-9]{4}|[0-9]{2})\b/;

Working Demo: http://regex101.com/r/gN5wH2

answered Dec 06 '13 at 18:00

anubhava

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He/she might *not* want the starting anchor in his/her regex though. – BlackVegetable Dec 06 '13 at 18:01
Crazy! Why did the anchor change things? – BlackVegetable Dec 06 '13 at 18:07
@BlackVegetable: See working demo and play with regex there. I have created a demo for you to understand better with color coding: http://regex101.com/r/oN1uO1 Basically optional `/` make it match last 4 digits without anchor `^` – anubhava Dec 06 '13 at 18:11
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Ah, that is subtle. On a related note, that tester is amazing. – BlackVegetable Dec 06 '13 at 18:16

DavidRR · Answer 2 · 2018-02-20T13:10:28.033

Since we're talking about a credit card expiration date, once you have validated the input date string using one of the fine regex expressions in the other answers, you'll certainly want to confirm that the date is not in the past.

To do so:

Express your input date string as YYYYMM. For example: 201409
Do the same for the current date. For example: 201312
Then simply compare the date strings lexicographically: For example: 201409 ge 201312.

In Perl, ge is the greater than or equal to string comparison operator. Note that as @Dan Cowell advised, credit cards typically expire on the last day of the expiry month, so it would be inappropriate to use the gt (greater than) operator.

Alternatively, if your language doesn't support comparing strings in this fashion, convert both strings to integers and instead do an arithmetic comparison.

forgivenson · Answer 3 · 2013-12-06T18:08:11.890

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Move a right paran:

^(0[1-9]|1[0-2])\/?(([0-9]{4}|[0-9]{2})$)

The end anchor wasn't being applied to the [0-9]{4} option, so more numbers were allowed.

edited Dec 06 '13 at 18:08

answered Dec 06 '13 at 18:00

forgivenson

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This still matches the last string. – Snowman Dec 06 '13 at 18:05
I see it matches the end of the last string (not the whole thing). Add the start of line anchor to fix that. See edit. – forgivenson Dec 06 '13 at 18:07

Regular expression to match credit card expiration date

3 Answers3

Working Demo: http://regex101.com/r/gN5wH2