What is the order when the system deducting my credits?

To put it simply, credits that soonest to expire will cost first. 

For example, if you are a Basic subscriber and have 100 credits rolling over from last month to this month, now you have 300 credits in total. When you use our products in this circumstance, the system will deduct the credits from last month first, because they are sooner to expire. And the system will start to deduct this month's credits only when the 100 credits from last month are used up.