We use many different tense forms to talk about future. In many cases, nearly all of these forms are possible with very similar meanings. However, in some cases, there is a difference of meaning.
Let me explain.
Study the example given below.
I will send the payment tomorrow. (Simple future)
I am sending the payment tomorrow. (Present continuous)
I am going to send the payment tomorrow. (Present continuous with going to)
I will be sending the payment tomorrow. (Future continuous)
As you can see, all of these forms express more or less the same idea, but there are subtle differences of meaning.
The simple future tense
Form: will / shall + infinitive
I will send the payment tomorrow.
I will apply for that job.
I will see him tomorrow.
I will wait for him.
I will come.
This form is mainly used to announce decisions that we have just made.
Notes: In British English, shall is commonly used with first person pronouns (I and we). Shall is uncommon in American English.
A: You haven’t sent the payment yet.
B: Don’t worry. I will send it tomorrow.
A: Have you finished that report?
B: No, I will finish it by Tuesday.
As you can see, these are all spontaneous decisions that were made on the spot.
Going to
I am going to find a job soon.
This form is used to talk about decisions that were made before we speak. Usually, we use going to to announce our intentions.
I am going to meet Janet next week. (I have already decided to do so.)
Compare these two forms.
Peter: They say the weather will be awful tomorrow.
Sam: Really? In that case, I will cancel the trip.
As you can see, this decision was made at the time of speaking.
Another example is given below:
Peter: They say the weather will be awful tomorrow.
Sam: I know. I heard the news. I am going to spend the whole day at home reading books.
Here, the second speaker is announcing a decision he has already made. If you use simple future here, you will still be understood, but you will sound unnatural.