You can always use whatever available balance you have on your credit card.  So yes, as long as you make the minimum payment and there is a remaining open balance you can use it.  However, in this situation you are being very risky for two reasons.  First of all, if you have maxed out your 500-dollar line of credit and only paid $50 on the balance, the interest on the remaining $450 will likely put you close to your limit.  This means that in actuality, you would not have $50 left to spend and trying to make a transaction for that amount may result in going over your limit or having your card declined.  Secondly, and most importantly, it’s never a good idea to max out your credit cards unless you plan to pay back a large part or all of the balance right away.  Potential lenders like to see that you are using your credit modestly and that you are not up to your neck in credit card debt across all of your accounts.