Future tenses

General information

I admit that talking about the future is one of the most confusing aspects of English. We don't just think about when we're going to do something, we also take into account how we consider it.
In Spanish there's not much difference between lo haré mañana and lo voy a hacer mañana. In English, however, we receive unspoken information according to what people say. I'll do it tomorrow, for example, tells us that the decision to do it has just been made. I'm going to do it tomorrow tells us that the decision was made earlier and that it is now an intention.
This may sound confusing, but in fact it's very precise. Just a little difficult at first...

Will
Structure: will do something
Will is used to talk about a future fact:

He'll be 24 tomorrow.
The Mayor will open the new musem next Tuesday.
The money will go into your account at the end of the month.

Will can be used to make a prediction:

I think it will be hot and sunny tomorrow.
If you take an aspirin, you'll soon feel better.
Valencia will win the league this year.

Will is also used to express an intention or decision made at the moment of speaking. Immediately after this decision, going to is probably the most appropriate form to use:

It's very hot in here. I'll open the window.
I'll have a cheeseburger and large fries.
Pub or cinema? No, I think I'll stay in instead.

Going to

Structure: going to do something

Going to is used to talk about a future intention when a decision has already been made:

When I leave university, I'm going to be a doctor.
They're going to meet us in the pub after the film.
When I leave school I'm going (to go) to university.

When we use 'going to go', we often omit 'to go' and just say 'going'.

Going to is also used to talk about future predictions when there is evidence that something is going to happen:

Look at those clouds. It's going to rain.
I haven't done any revision. I'm going to fail the exam.
He's beaten all the other players. He's going to score!

Present simple

The present simple is used to talk about future timetables, itineraries and so on.

My train leaves at 9 o'clock tomorrow night.
My birthday falls on a Friday this year.
The match starts at 3 o'clock.

Present continuous

Spanish people are not generally happy using this because it sounds strange to them. However, English people use it all the time to refer to the future.

It's used to talk about future arrangements (a word which doesn't have an exact translation in Spanish). An arrangement is similar to an intention, but involves more preparation or organisation. In other words you have to phone someone, or put it in your diary, or promise yourself something.

I'm having lunch with my parents tomorrow. (I rang them)

He's leaving work at the end of the month. (He's told his boss)

She's meeting me in the pub later. (We spoke to each other at the end of class)

I'm seeing that film tomorrow afternoon. (I promised myself)

Future continuous

Structure: will be doing something

The future continuous is used to talk about an activity that will be in progress before and after a particular time:

Don't ring me at 9 o'clock. I'll be having dinner.
This time next week I'll be lying on the beach wondering what to have for lunch.
Don't come so early. I'll still be getting ready.

It is also used to refer to a future event that will happen in the normal course of things, in other words it doesn't have anything to do with intentions, time of decision, type of plan etc. This event will occur as time passes. Imagine how you use the present continuous to talk about what's happening now (I'm using my computer, etc). Now think about the future, and that's how we use the future continuous (I'll still be using my computer in half an hour).

The guests will be arriving any minute now.
The company will be opening a new branch in London next year.
The teachers will soon be giving you details of next year's course.

Future perfect

Structure: will have done something/will have been doing something

The future perfect is used to talk about an action that will be completed before a specific time in the future.

I'll have finished the report by 6 o'clock.
They will have decorated the house before we move in.
They'll have been married fifty years next anniversary.
You'll have received payment by the end of the week.
He'll have been working for the same company for thirty years next month.