Future time can be expressed in several ways:
There are no definite boundaries between them - many situations don't belong clearly to only one category:I'm going to meet them at 6.
Will is the default way of expressing future time:
Be going to is used when something is already 'on the way':
because we have decided to do it:
or because of a present cause:
We use the Present Progressive with situations we are in the middle of:
We can also use it when we are in the middle of arrangements for a future event:
The Present Simple is used for future events which are impossible to change:
programmes, schedules and timetables:Hurry up, the bus comes at 8:20.
calendar and cyclic events in nature:Tomorrow is Friday.
Will is also possible in the examples above.
We use the Future Progressive with situations we will be in the middle of:
But it has a separate use - the Future Progressive avoids the meaning of intention, promise etc.:
Be going to is usually replaced by will later in the text:Monday is going to be another dry day.