Unit 20. (I'm) going to (do)

'I am going to do something' = I have already decided to do it.

• A : There's film on television tonight. Are you going to watch it?
  B : No I'm tired. I'm going to have an early night.
• A : I hear Ruth has won some money. What is she  going to do with it?
• B : She's going to buy a new car.

I am doing and I am going to do

We normally use I am doing (present continuous) when we say what we have arranged to do ~

• What time are you meeting Ann this evening?
• I'm leaving tomorrow. I've got my plane ticket.

'I am going to do something' = I've decided to do it. (but perhaps not arranged to do it)

• The windows are dirty. Yes, I know. I'm going to clean them later.
  = I've decided to clean them but I haven't arranged to clean them.

Often the difference is very small and either form is possible.

 

'I was going to (do something)' = I intended to do it but didn't do it

• We were going to travel by train but then we decided to go by car instead.
• I was just going to cross the road when somebody shouted 'stop'.

You can say that something was going to happen (but didn't happen)

• I thought it was going to rain but then the sun came out.