A Present, past and future
Read this paragraph from Rachel’s letter to her aunt and uncle.

This is my last year at college, so I’ll be leaving in June. And I’ve already got a job! In
September I’m starting work at a bank in London. So I’ll be free for most of the
summer. I’m going to spend six weeks travelling around the US. My friend Vicky is
coming with me. (She finishes college at the same time as me.) We’re really looking
forward to the trip. We might go to Canada too. Vicky has friends in Toronto.

When we talk about the present or the past, we use verb forms to say what is happening now, what
happened yesterday, and so on. Vicky has friends in Toronto.

We know about things in the present and in the past because they are already real. But talking about the future is more of a problem. There is no single form in English that we can always use for the future. There are many different ways of talking about the future, depending on how we see a future event. It may be something that is fairly sure to happen, but on the other hand it may be just a plan or an intention, or it may be something that you think will happen but you can’t be sure about.
B Verb forms used for the future
Here are some examples of verb forms used to express the future.
Be going to I’m going to spend six weeks in the US. (an intention)
Will I’ll be free for most of the summer, (neutral future)
Present continuous         I’m starting work in September, (an arrangement)
Present simple                   She finishes college at the same time, (a timetable)
Will be doing I’ll be leaving in June, (in the course of events)

Very often there is more than one possible form that could be used.
She’ll finish college in June. She finishes college in June.
She’s finishing college in June. She’ll be finishing college in June.
Rachel could use any of these in her letter.
C Will
We often use will as a neutral way of expressing the future, but it is not ‘the future tense’. It is only one of the forms we can use. In some situations will is not the right word.
After college I’m going to travel around the US. Here Rachel is saying what she intends to do in the future. We cannot use will here.
D Being sure and unsure
We cannot always be sure about the future. To show that we are unsure we
can use might or could
We might go to Canada. It could snow soon.
To show how sure or unsure we are, we often use phrases like I’m sure, definitely, I expect, I (don’t) think and probably.
I’m sure it’ll be all right. We’re definitely going to be at the meeting.
I expect everyone will be going home. Rachel will probably be late.
I think I’m going to sneeze. I don’t think Tom’s coming tonight.

 

Source : Oxford Practice Grammar