You just have to watch it. Soldiers earn 2.5 days of leave per month while on AD. At most, your BCT is going to be 2.5 months which would give you 6.25 days of leave.
If you end up in a situation like I did, my BCT fell over Christmas Exodus which was approximately 14 days of leave. This made me go in the hole on leave, and then "debt repayment" began when I resumed normal drills. I spent the next 5 months and an AT paying that back in little chunks. They don't really give you the choice either, it just comes out of your pay automatically based on some percentage of what you owe.
Now you'll hear about doing the hometown recruiter thing for paying off some of your leave time during a break like that, but unfortunately my BCT company wouldn't accept those forms from any of us NG soldiers.