Future Tense(1)

Will and Be going to
I think I will go home at 4 today.
I think I am going to go home at 4 today.

When I am sure about the future:
I will go for a walk later today.
I am going to go for a walk later today.
No difference

Predictions about the Future:
He is going to graduate this year.
He will graduate this year.
No difference

A Prior Plan
= a plan that we made before we speak
BE GOING TO
I am going to see my friend this weekend.
(We talked last night and decided we both were free.)
Not WILL