The future simple is used to express future time.

I will be happy to help you anytime!

I am going to go Spain tomorrow morning!

Our staff will answer your calls between 8am and 5pm.

The future simple is in itself a fairly straightforward tense to explain and form. Its usage however often creates problems to English language learners, who find it hard to know when to use will and be going to (along with the present continuous‏‎ used to talk about the future).

Will

We use will to make predictions and promises.

It will rain, you wait and see.

I swear that I will be the best president for this country!

We can also use will when we just decide to do something (i.e. a spontaneous action):

I think I heard someone at the door; I’ll get it.

I’m bored. Tell you what, I’ll make us a cup of tea.

More formally, it’s used to talk about planned events in the future:

The game will begin at 4 o’clock precisely.

The train will leave at 7.15 in the morning.

NB we can also use shall instead of will sometimes; for more on this see the links below.

Form

Very simply, we use will with a infinitive form of the verb‏‎:

will + {verb}

I will see you tomorrow.

Note that will is sometimes abbreviated to ‘ll in informal speech and writing.

I’ll see you tomorrow.

Be Going To

We use be going to to talk about planned events in the future:

I am going to see her tomorrow.

They’re going to arrive on the 3.30 train.

We also use it to talk about intentions or predictions based on what we can see or feel now:

I am going to pass my test, I’m sure of that!

Look at those clouds; it’s going to rain for sure.

Form

As with will above, the form is used with the infinitive:

be going to + {verb}

They are going to stay here tonight.

Will vs Be Going To

Sometimes it is difficult to choose between be going to and will:

It will be fine tomorrow.

It is going to be fine, tomorrow.

Some grammars‏‎ will tell you that will is for on spot decisions, offers and predictions and that be going to is for plans intentions or obvious predictions. But this isn’t always true and we can make snap decisions and express them with be going to:

Right, that’s it, I’m going to go now!

Practically speaking there’s little to choose between using will and be going to in many circumstances. Using will implies that we are speaking about a fact rather than an opinion but even then there are occasions when either is appropriate.

In a classroom situation in most cases it is not worth pointing out when a student has chosen one form over another as there are almost certainly cases where either form can be used.

Useful Links

Future‏‎ Tenses in English Grammar – an overview of the different ways to talk about the future in English.

All About Shall (vs Will) – the difference between shall and will and when we use them.