I don't have a formula either.
I pay my bills on time too but I used to have a lot of accounts that I opened up at stores, cc promotions, etc. All of them with barely used and with zero balances. Then I had a friend of mine (a business major) once tell me that just having all those accounts is detrimental to my FICO, so I closed a bunch of them.
I'm wondering, is there any truth to that? Can anyone else confirm this?