Credit scores are formulated from formulas that noone knows for sure. When working with credit for a while, you can guestimate what makes a difference and what doesn't. There are lots of urban legends about what and what doesn't affect the score.

One very important variable is the ratio of balances to high limit. This is a ratio calculated from all of the outstanding balances vs what your max limits on all accounts are. In other words, if everything is maxed out.....even if you pay everything on time, your score will not be as high as it could be because you are considered "over extended". So, paying off an account and CLOSING it is not always the best course of action if scoring is the priority. That closed account is one LESS account towards that ratio. Paying it off or atleast down below 30% of the high limit but LEAVING IT OPEN will substantially increase your score vs paying it off and CLOSING IT alone.

Another thing that affects score and also ties in with the mentioned above is length of time account is in good standing. New accounts typically drop your score, whereas old accounts help it (as long as of course you pay it on time and keep the balance below 30% of the max). Typically, credit scores drop a little in the couple of months right AFTER you get new credit.

Obviously, how you pay affects the credit score the most. Old collections, past due accounts, bankrupcies, settlements, etc. all stay on for a very long time if not settled in full. They can even "re-up" or re-update the old account every 5-7 years technically making an old account "new" and therefore messing up your credit for yet another 5-7 yrs.

There are many more fallacies about scores. There is no real guarantee as to how much or how quick or exactly how much your making certain choices will make on your scores. The actual formulas are only known to the specific agencies themselves. So, there is no real exact way to know, only guestimates.