Thanks for the info, everyone. The primary is extremely financial responsible and carries no debt. Is able to make expensive purchases and always pays off balance once statement hits. This was the first time I noticed. I’ve been an AU on this account for over 20 years. It’s probably happened before but I didn’t pay attention. Now that I know what happened I won’t panic. Interestingly, I went on the payments tab in my online account today and could see the full balance. So that is indeed what caused the increase in balance.