Choosing the structure to use to express the future is one of the most difficult areas for learners. It is best for the speaker to consider how he or she is thinking about the future situation or activity, not about the situation or activity itself.
* Will/Won't is used to give simple facts about the future.
I'll be 65 in June.
* Will/ Won't is used to make predictions based on your opinions.
It won't be easy to get a new job.
* May, might and will with I think, I guess, maybe, probably, etc., are used to talk about future activities, facts, situations, and predictions when the speaker is less than 100 percent certain about them.
I may go on for a master's degree.
I might not be able to go.
It might rain.
We'll probably move to Arizona.
* Going to is used to talk about plans or decisions already made.
I'm going to retire in June.
* Going to is used to talk about events that are already in progress or on the way.
We're going to have a baby.
* Going to is used to talk about predictions based on current evidence or knowledge.
It's going to snow tonight.
The present continuous is used to talk about planned events and activities. It is often used to talk about fixed arrangements with times and places.
What are you doing this weekend? = What arrangement have you made?
I'm graduating in June. = This is a fixed date.
Be able to
* The form be able to is similar in meaning to can. It is followed by the base form of a verb.
* It is used frequently after modal verbs.
I hope I'll be able to go.
I might not be able to afford it.
* It is also commom after would like to and going to.
I'd like to be able to go.
I don't know if I'm going to be able to go.
Cambridge University Press.