Be going to is used when we want to emphasise our decision or the evidence in the present. Be going to is often used in a similar way to will
There are several grammatical structures in the English language to describe future activities. Three of them are the present simple tense, present continuous tense and be going to + verb.
Present tenses for future
With the future time expressions (next Friday, tomorrow) both the present simple and present continuous are used for definite plans and arrangements in the near future. The future time must be mentioned, otherwise the sentence would have a present meaning.
I am watching TV. (a present activity: I am doing it just now.)
I am watching TV tonight. (a future activity – I will do it tonight, it is my plan.)
The present continuous for future is more personal and informal.
I am leaving on Sunday. (I have decided to leave on Sunday, it is my plan.)
I leave on Sunday. (Someone else has decided it, it is someone’s plan for me.)
The present simple for future is typically used in official statements and timetables.
The new shopping centre opens on 1 March.
The bus arrives at 6.55.
The present continuous is the most usual way of expressing one’s personal plans in the near future.
We are going on holiday to Italy in summer.
Be going to
1. Be going to + verb is used to show intentions. We use this structure for decisions that we made before the moment of speaking.
I am going to clean the car and you can pack the suitcase.
We are going to reconstruct our house.
2. Be going to is also used to express your opinion that something is certain to happen. There is evidence for your prediction.
Our team is going to win. (It is 4:0 and two minutes left. I am sure we will win the match.)
The planes are going to land. (They are coming closer and closer to the airport.)
Sometimes we can use either the present continuous or be going to with a little difference in meaning.
I am travelling to France in May. (my personal plan)
I am going to travel to France in May. (my personal intention)