Information is constantly being supplied to our credit files. If you ever wonder why your scores won't stay the same every time you pull it, especially if the same accounts are reporting monthly, it's because the data on those accounts are changing daily.
~ Payments Made
~ Payments Missed
Also, closed and negative accounts are getting older, thus FICO scores it differently.
The key is to monitor for significant changes and fluctuations, that would signal an error, accounts you may not be aware of, or signs of identity theft.
By law, U.S. consumers are now entitled to a free copy of their credit report once annually. To get yours, visit a site such as AnnualCreditReport.com. You can pay extra for a scores, if you wish, but for now check out the data to ensure it's 100% accurate, complete, verifiable and timely.
If you need help learning how to read it and identify errors, check out my free 5-Day Credit Challenge: bit.ly/UnderstandMyCredit
Hope this helps!