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I had a general question about card numbers. Say there are 3E9 people on Earth, each with 3 cards. That's around 10 digits right there. There's 1 digit for che

I had a general question about card numbers. Say there are 3E9 people on Earth, each with 3 cards. That's around 10 digits right there. There's 1 digit for checksum. I imagine you'd want to leave space for least 1000 financial institutions around the world, so that's another 4 digits. Which means you can only have 100 transactions per person. None of this takes into account the fact that the same people are issued way more than 3 card numbers either. So my question is, how are we not close to running out of card numbers? How is this not even a problem yet?

umeshunni 11y ago
The short answer is that, in theory, we are running out. It's kept in check now by some amount of BIN & account number recycling by financial institutions. If you're curious about the number scheme, check out https://en.wikipedia.org/wiki/ISO/IEC_7812 https://en.wikipedia.org/wiki/ISO/IEC_7812
- codelitt 11y ago
  I don't believe we are that close to running out though, are we? Using the number scheme, this person calculated^1 that (assuming Amex starts issuing 16 digit cards) there would be 3*10^14 + 10^11 or 4.001e+14 possible combinations. [1]: https://www.reddit.com/r/theydidthemath/comments/3wj8eb/request_how_many_different_number_combinations/cxwmb7j https://www.reddit.com/r/theydidthemath/comments/3wj8eb/requ...
ball_of_lint 11y ago
This actually wouldn't be much of a problem for privacy because they could just have x different cards and cycle them through and just keep very good books on who got what.
ethagknight 11y ago
The date adds a few more digits, right?
driverdan 11y ago
> Say there are 3E9 people on Earth, each with 3 cards. You vastly overestimate the number of people with credit cards.
- scrollaway 11y ago
  It averages out. The people who do have credit cards are issued far, far more than 3 numbers in their lifetime due to cards expiring/being cancelled, promotional offers etc. I myself have had something like 10-15 different card numbers in the past 10 years, without actually trying.
- wfunction 11y ago
  I wasn't trying to come up with a lower bound, I was trying to make the numbers round off nicely and reasonably to make a point.

umeshunni 11y ago

The short answer is that, in theory, we are running out. It's kept in check now by some amount of BIN & account number recycling by financial institutions. If you're curious about the number scheme, check out https://en.wikipedia.org/wiki/ISO/IEC_7812 https://en.wikipedia.org/wiki/ISO/IEC_7812

codelitt 11y ago
I don't believe we are that close to running out though, are we? Using the number scheme, this person calculated^1 that (assuming Amex starts issuing 16 digit cards) there would be 3*10^14 + 10^11 or 4.001e+14 possible combinations. [1]: https://www.reddit.com/r/theydidthemath/comments/3wj8eb/request_how_many_different_number_combinations/cxwmb7j https://www.reddit.com/r/theydidthemath/comments/3wj8eb/requ...

ball_of_lint 11y ago

This actually wouldn't be much of a problem for privacy because they could just have x different cards and cycle them through and just keep very good books on who got what.

ethagknight 11y ago

The date adds a few more digits, right?

driverdan 11y ago

> Say there are 3E9 people on Earth, each with 3 cards. You vastly overestimate the number of people with credit cards.

scrollaway 11y ago
It averages out. The people who do have credit cards are issued far, far more than 3 numbers in their lifetime due to cards expiring/being cancelled, promotional offers etc. I myself have had something like 10-15 different card numbers in the past 10 years, without actually trying.
wfunction 11y ago
I wasn't trying to come up with a lower bound, I was trying to make the numbers round off nicely and reasonably to make a point.