I will and I’m going to

Future actions

Study the difference between will and (be) going to:

Sarah is talking to Helen:
SARAH: Let's have a party
HELEN: That's a great idea. We'll invite lots of people.

will ('ll): We use will to announce a new decision. The party is a new idea.

Later that day, Helen meets Dan:
HELEN: Sarah and I have decided to have a party. We're going to invite lots of people.

(be) going to: We use (be) going to when we have already decided to do something. Helen had already decided to invite lots of people before she spoke to Dan.

• 'Gary phoned while you were out.'  'OK. I'll call him back.'
  'Gary phoned while you were out.'  'Yes, I know. I'm going to call him back.'
• 'Anna is in hospital.'  'Oh really? I didn't know. I'll go and visit her.'
  'Anna is in hospital.'  'Yes, I know. I'm going to visit her this evening.'

Future happenings and situations (predicting the future)

• I think the weather will be nice later. or
  I think the weather is going to be nice later.
• Those shoes are well-made. They'll last a long time. or
  Those shoes are well-made. They're going to last a long time.

• 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.