‘Will’ and ‘going to’ are the two forms of simple future used in English. They are used more or less interchangeably, but there are certain subtle differences between them that even many experienced English speakers are not aware of. The main rule to keep in mind is that: if the decision to act was made before the time of speaking, ‘going to’ must be used; if not, ‘will’ must be used.

Will

There are two primary distinct uses for ‘will’:

1. To express voluntary action. Voluntary action refers to the following:

a. Any action that the speaker offers to perform.

    - I will take you up on that offer.

    - I will get you your breakfast in bed.

b. Any action that the speaker declines to perform.

    - I will not (won’t) be able to come for your party.

    - I will not do your work for you.

c. Any action that the speaker requests the listener to perform.

    - Will you come home on Friday night?

    - Will you take me to the amusement park?

2. To express a promise.

    - I will come back to work as soon as I make a full recovery.

    - I will call you later tonight.

Going to

There is one primary distinction for use of ‘going to’: it is used to express plans, i.e. the intention of the speaker to do something in the future. This can take two forms:

1. To state such an intention:

    - I am going for the match on Thursday.

    - I am going to ensure that we have fun on this trip.

2. To ask about such an intention:

    - Are you going to watch the match on Thursday?

    - Are you going to Jaipur with the others?

Will/Going to

Both ‘will’ and ‘going to’ can be used when making predictions about the future.

    - It looks like it will rain today. = It looks like it is going to rain today.

    - I don’t think he will do it. = I don’t think he’s going to do it.