Future

We use a number of difference verb forms to refer to the future (= "the time after now") in English.
(1) will + Verb
(2) be + going to + Verb
(3) Present Simple
(4) Present Progressive
(5) will + be + Verb-ing (and other forms)

1. Will

There is a future auxiliary will (or 'll ) + Verb which is used in the following ways.

1.1. Prediction

We use will + Verb for prediction or describing something we know, or expect, will happen. Let's see examples below.
(1) It'll be windy tomorrow. There will be rain in places.
(2) My horoscope says that next year will bring me success and happiness.

1.2. Immediate future decision

We use will + Verb to express a decision about the immediate future. Let's see examples below.
Ex: "Which t-shirt do you want?" "I'll take the white one, please."

2. Be + going to + Verb

This is very frequently used to talk about plans or intentions. The decision has been made before the moment of speaking. Let's see examples below:
(1) "Do you remember that job I was talking about? I'm going to accept it." "Ah, good, you've made up your mind about it."
(2) "What are you going to do when you grow up?" "I'm going to be a policeman."

Be + going to is also used for something in the future for which we have present evidence. Let's see examples below:
(1) It's going to rain. ("I can see the clouds.")
(2) John's running well. He's going to* break a few records this afternoon.
(3) The doctor said, "You're going to have to have some some surgery."

* Very often we can use either will or be going to for the same predictions. For example, in (2), we could say: "He'll break a few records this afternoon." But in the main clause of conditional sentences we cannot usually replace will by be going to.
Ex: If you take this road you will get home quicker. (NOT: If you take this road you are going to get home quicker.)

How to choose between will and be going to in expressing the speaker's or hearer's intention:
Especially in speech we often use will and be going to to express intention. But the meaning can be slightly different:
(I) Will focuses on what intentions are formed at the moment of speaking; for example, when we make a promise or an offer, or ask for a decision:
(1) "The bus has gone. What will you do now?" "Don't worry - we'll order a taxi."
(2) "I'll see you tomorrow, okay? Bye."

(II) Be going to talks about an intention we already have:
(1) "What are you going to do this evening?" "I'm going to put my feet up and rest."
(2) "This year we're going to rent a cottage in the country."

3. Present Simple

The Present Simple is used for future certainties: for example, for times fixed in time-tables, in the calendar, in our diary. Let's see examples below:
(1) It's the 4th of March next Monday, isn't it?
(2) My English language course finishes next week.
(3) What time does your plane take off?

The Present Simple is more often used for the future in some subordinatte clauses. We use the Present Simple instead of will mainly in clauses of time and in conditional clauses. Examples of words which begin these clauses are:
(1) If : If it snows, the match will be cancelled.
(2) When : When the princess arrives, the band will play some music.
(3) While : I'll take a photo while you are on the dance floor.
(4) Before : Before the princess arrives, the band will play some music.
(5) Until : Let's wait indoors until the train comes.
(6) After : After the princess arrives, the band will play some music.
(7) Unless : Unless I find the tickets, we won't be able to go to the theatre.
(8) As soon as : I'll call you as soon as I'm ready.
(9) In case : I'll bring an umbrella, just in case it rains.

There are also some that-clauses and WH- clauses which have a Present Simple verb for the future. For example, after hope, whatever, or which:
(1) I hope (that) you have a pleasant journey.
(2) Don't get lost, whatever you do.
(3) The team which wins tomorrow's match will be the best team in the world.

4. Present Progressive

This structure is used for talking about future plans or arrangements (but these plans are not so fixed as with the Present Simple). Let's see some examples below:
(1) I'm meeting him next week.
(2) Next summer, the rock group is touring the U.S.A.
(3) Their friends are driving to England at the weekend.
(4) "When are you leaving?" "On Sunday."

5. Will + be + Verb-ing (and other forms)

These are some other ways of talking about the future:
(1) Will + be + Verb-ing (future progressive):
Ex: Next week I'll be talking about how to use a microphone.

(2) Is + to + Verb or are + to + Verb:
Ex: The USA President is to visit Canada.

(3) Be + about + to + Verb (= near future)
Ex: The mayor is about to announce the result of the election.

(4) Be + on the point of + Verb-ing (= near future):
Ex: The oil company is on the point of making an important decision.

I hope this article helps. If you have any question, please leave a comment below.