Some credit card companies refuse to provide information on customer's credit limits to the credit bureaus, I'm looking at you Capitol One (Note: They stopped doing this recently). Since the credit bureaus need this information to calculate your credit score, they are forced to estimate your limits based on the information they do have, namely your monthly balances. A common technique is to assume the highest balance you have ever had on a card is your credit limit, which is going to be lower than your actual credit limit if you never max out your cards, and consequently make your utilization % higher.
Now why, one must ask, would a credit card agency refuse to provide this information that might wind up reducing the credit scores of their valued customers? I mean if those customers had worse credit they would have to pay higher interest rates and..... Ohhhhhh!
Even if you pay off your balance in full each month, it doesn't mean your utilization for that card is $0/credit limit. Your payment cycle and how it correlates to their reporting cycle force them to use a snapshot on the day the reports are due that may not represent the true nature of how you are paying your cards.
Paying off credit card balances in full every month is an excellent
credit habit, but doesn't mean that one's lender will report a zero
balance to the credit bureaus," says Craig Watts, spokesman for FICO,
the company whose credit scoring model bears its name.
That seems to be what's happening to you. According to Steve Katz,
spokesman for credit bureau TransUnion, banks generally report a
cardholder's account information to the bureaus about once every 30
days, but it can really vary. For example, Chase says it reports the
current card balance on the 13th or 14th of every month. Citi,
American Express and Wells Fargo each say it reports the account
balances listed on cardholders' monthly statements. Bank of America
says it reports account balances 30 to 45 days after payment is
Source: "Improving a great credit score comes down to timing"