Both going to and present continuous are used to talk about future actions and events that have some present reality. So, for example, if we say that something is happening or going to happen, it is usually already decided or planned.
We are going to get new windows.
We are getting new windows.
As you can see, both sentences express nearly the same idea.
Both present continuous and be going to can be used to express the same idea. In some cases there is a difference of meaning.
The present continuous tense is common with verbs of movement.
I am just popping out to the café.
Are you coming to the party?
The present continuous tense is mainly used to talk about personal arrangements and fixed plans. Be going to can also be used to express the same idea; however, it puts an extra emphasis on the idea of intention.
- I am going to get a new job. (= I intend to get a job.)
- I am getting a new job. (= It is already decided / arranged. Here the focus is on the arrangement.)
- What are you doing this evening? (A question about arrangements)
- Are you going to do anything about that letter you received from the civic authorities? (A question about the intentions of the listener)
- I am seeing Peter tomorrow. (Here the emphasis is on the arrangement that already exists.)
- I am going to ask him to stop borrowing my car. (Here the emphasis is on the intentions of the speaker.)
Events outside people’s control
We do not normally use the present continuous to talk about events that are outside people’s control.
- It is going to snow before long. (NOT It is snowing before long.)
- Look at the sky. It is going to rain.
- Prices are going to fall.
The sentences ‘It is raining’ and ‘Prices are falling’ have altogether different meanings. They are used to talk about actions or situations that are in progress at the moment. Be going to is only used to talk about future events