• Will functions as an auxiliary of the future in simply predicting a future event: The Queen will open the new hospital next Thursday.
• Will can also function as a modal auxiliary to express ideas of willingness and spontaneous intention: Will you help me for a minute? 'There's no more milk!' 'I'll go and get some.'

• Going to expresses a premeditated intention: I'm going to decorate the bathroom this weekend.
• Going to is also used to predict a future event for which there is some evidence now: Great news! I'm going to have a baby!

• The Present Continuous is used to express an arrangement, usually for the near future.
• It is wrong to use the Present Simple in this sense.
• The Present Continuous cannot be used to express an event that has not been arranged by human beings: *It's raining tomorrow.

• The Present Simple is used to express a future event which is seen as being certain because of a timetable or calendar: What time does the film start? My train gets in at 11.00.

• The Future Continuous expresses an activity that will be in progress around a specific time in the future: Don't phone at 8.00 — I'll be having supper.
• The Future Continuous also expresses an action that will occur in the natural course of events, independently of the will or intention of anyone directly concerned: In a few minutes we will be landing at Heathrow Airport.
• The Future Continuous is often used to express a casual or polite question about someone's future plans — related to the use that it can express an action that will occur independently of the will or intention of the people concerned: Will you be bringing Kate to the party? (polite inquiry, not imposing)

• The Future Perfect expresses an action that will be completed before a definite time in the future: I'll have finished my work by the time you get back.

In formal contexts, an arrangement is sometimes referred to as something that is to happen. This usage is frequently found in news reports.

Sometimes when we are talking about the past, we want to refer to something that was in the future at that time. This is called the 'future in the past', and it is expressed by was/were going to, the Past Continuous, or would, and was/were to.