A credit card statement is one of the few times when a negative number is a good thing financially. Charges on a credit card, which increase your balance, show up as a positive number on a statement. Payments and credits, on the other hand, post as negative numbers. If you're paying your bills on time, which you should if you want to avoid interest charges, the negative numbers on your credit card statement will equal or exceed the total of the charges you incur.
TL;DR (Too Long; Didn't Read)
Negative numbers on a credit card statement indicate credits or payments. These negative numbers are used to offset charges, which are listed as positive numbers.
Credit Card Statement Formatting
Credit card companies generally list purchases as positive numbers and refunds as negative numbers. For example, if you purchase a shirt from a retailer for $25, you'll see a line item on your statement for $25. If you return the shirt for a refund, you'll see a negative $25, or $25 in parenthesis. When you make a payment from your checking or savings account to pay off your credit card, the payment will also appear as a negative number.
Credit Card Balances
If you want to pay off your credit card in full, you'll need to make enough payments to offset all your charges. In credit card statement accounting, your negative line items must equal your positive line items, which are your charges. However, if you overpay the account, your negative entries will exceed your positive balance, leaving you with a credit. For instance, if you pay $100 to your credit card company when your balance is $75, you'll have a $25 credit balance. That credit will remain on your account until you charge something, at which time that credit will help offset the new purchase. You can also request a check from the card issuer to pay back the amount that they now owe you.
One way that you could end up with a credit balance is if you make a return. If you forgot that you returned something during the month, for example, and just pay off the statement balance from the prior month, you might end up with a credit. The same is true if you receive a statement credit for qualifying promotional activity that your credit card company might offer, such as a $150 credit for opening a new account and spending a minimum amount over a certain period of time.