"My passport will expire in three months."
This sentence is from my textbook. I'm wondering why it's not written as "My passport *expires* in three months."
Here is an example from LDOCE Online:
My driving licence expires in March.
In this case, it goes with the present tense, which is grammatically correct to me, because we're taught that when it comes to a sure thing to happen in the future, we should use the present tense instead of the future tense. Why is this sentence in the future tense? Is it correct? I have a feeling that it may have something to do with "in three months," right? Thank you.