Dear Liz: am going to pay off one of my daughter’s private student loans. One has a balance of $8,500 at 4% interest and the other is for $7,500 at 6%. Which one should I pay off?

Answer: You have a lucky daughter, either way.

In addition to balances and rates, the other variable you need to consider is whether the rates are fixed or adjustable. These days, many private student loans have fixed rates, but in the past most of this debt had variable rates. Variable rates mean higher costs and larger payments when interest rates rise.

If both loans have variable rates, or both are fixed, then paying off the highest rate debt first makes the most sense. If the lower rate loan is variable and the higher rate one is fixed, you’ll have to guess whether interest rates are likely to rise enough in the next few years to instead pay the larger balance first. Some people might want to pay off a variable debt just to eliminate the uncertainty, while others are willing to gamble that rates aren’t likely to jump two full percentage points before the loan is scheduled to be paid off.