Only the credit scoring companies can tell you for sure - they do not publish their criteria. The best guessers contend that the total amount of credit available to you and the total balance as a percentage of the available use are key issues in your score. If you agree with this contention, then you should keep the credit line open and not use it while you pay it down - if you want your sibling off the account, you might be able to transfer the balance to a new account that she does not have access to while maintaining the credit limit. As you pay down, your score should increase. If you close the account, the credit limit will decrease as your balance decreases, so it will appear that you are maxed out on that account. Depending on how much other credit you have and what percentage is used will be determinative of your resulting score.