The Future – Differences between going to, present continuous and will
Basically we use to be going to when we intend to do something, we are probably going to do it but we have not confirmed it 100%.
I‘m going to watch the match tonight.
I‘m going to meet my friends tomorrow.
I‘m going to eat pizza tonight.
If I now call the pizzeria to book a table for two for 8 o’clock this evening I can say:
I‘m eating pizza this evening. (Because I’m sure)
I‘m going to fly to Brazil next month.
If I now buy my tickets, I can say:
I‘m flying to Brazil next month. (Because I’m sure)
Note that if I say:
I‘m going to fly to Brazil next month after I buy the tickets, it’s ok.
To be going to is always correct when we talk about a plan even if it’s sure. The present continuous is correct when we talk about a plan. Will is only correct when we talk about a plan if we say “I think…” or “maybe” or something similar.
We use will when we decide something now.
Who would like to come to the cinema?
I hadn’t thought about it before so it is not a plan. I decide at the same time as I speak.
So we use will when we decide at that moment to do something.
You go into a cafe and your friend says:
What would you like to drink?
I‘ll have a coke, please.
You didn’t think about it before you went into the cafe, you decided when your friend asked you. So it wasn’t a plan and so you use will.