Study the difference between will and (be) going to:
Sue is talking to Erica:
Sue : Let’s have a party.
Erica : That’s a great idea. We’ll invite lots of people.
Will (‘ll): We use will when we decide to do something at the time of speaking.
The speaker has not decided before. The party is a niw idea.
decision now |=== I'll ... ===> past __________ now _______ future
Later that day, Erica meets Dave:
Erica : Sue and I have decided to have a party. We’re going to invite lots of people.
Dave : –
(be) going to : We use (be) going to when we have already decided to do something.
Erica had already decided to invite lots of people before she spoke to Dave.
decision before |======= I'm going to ... ===> past __________ now _______ future
“Daniel called while you were out.” “OK. I’ll call him back.”
“Daniel called while you were out.” “Yes, I know. I’m going to call him back.”
“Anna is in the hospital.” “Oh really? I didn’t know. I’ll go and visit her.”
“Anna is in the hospital.” “Yes, I know. I’m going to visit her tonight.”
Future happenings and situations (predicting the future)
Sometimes there is not much difference between will and going to. For example, you can say:
I think the weather will be nice latter.
I think the weather is going to be nice latter.
When we say something is going to happen, we think this because of the situation now
Look at those black clouds. It’s going to rain. (not It will rain)
(We can see that it is going to rain from the clouds that are in the sky now.)
I feel terrible, I think I’m going to be sick. (not I think I’ll be sick)
(I think I’m going to be sick because I feel terrible now.)
Do not use will in this type of situation.
In other situations, use will:
Tom will probably get here at about 8:00.
I think Jessica will like the present we bought for her.
These shoes are very well made. They’ll last a long time.