English/Parts of Speech/Verbs/Tenses/Future with 'going to' and 'will'

When talking about a planned or arranged future, 'going to' plus an infinitive is used:

• I'm going to buy a new computer next week.
• John is going to call me later.
• We are going to go on a date this weekend.

On the other hand, 'will' is used for decisions made at the time of speaking:

• I will call Bob now and see when he is coming.
• I will see who is at the door.