How various credit card numbers are on a visa credit card?

Pretty much all credit cards own sixteen, but if you're trying to fake one...er, they hold a pattern to them, so upright luck guessing a pattern that corresponds beside an expiration date.

Answers: Credit cards have 16, except for American Express which I believe have 15 numbers

On a side note...

All American Express cards start next to 3
All Visa cards start with 4
All Mastercards start next to 5
All Discover cards start with 6

And specifically your useless fact for the time. :)

four groups of four totalling 16