We use will to talk about plans decided at the moment of speaking.
- I forgot to phone my mum. I’ll do it after dinner. He decides to phone his mum when she is speaking – she didn’t have a plan.
- I can’t decide what to wear tonight. I know. I’ll wear my black dress.
- There’s no milk in the fridge. I’ll buy some when I go to the shops.
We use going to to talk about plans decided before the moment of speaking.
- I’m going to phone my mum after dinner. I told her I’d call at 8 o’clock. He decided to phone his mum before he speaks – he already had a plan.
- I’m going to wear my black dress tonight. I need to pick it up from the cleaners.
- I know there’s no milk. I’m going to get some. It’s on my shopping list.
We can also use the present continuous to talk about future plans. We usually use it when the plan is an ‘arrangement’ – more than one person is involved and we know the time and place.
- I’m meeting Jane at 8 o’clock on Saturday.
- We’re having a party next Saturday. Would you like to come?
- Are you doing anything interesting this weekend? We often use the present continuous to ask about people’s future plans.