Observe the following examples to know the difference between “to be going to and will”:
- I’m going to get married on 1 June 2012.
- I will catcth the mouse, if it comes into the room again.
- I’m going to turn on the lamp because it’s dark.
- I will play poker with my friend tomorrow.
“To be going to” is used to tell a fixed plan. But “will” is used to tell a prediction about something.
We may use “to be going to” to tell something that has been planned. But “will” is used to tell something that it may happen or not in the future.