A. You can use I’ll … (I will) when you offer or decide to do something
My bag is very heavy.
I’ll carry it for you.
Bye, I’ll phone you tomorrow, OK?
We often say I think I’ll … / I don’t think I’ll … when we decide to do something:
‘My bag is very heavy.’ ‘I’ll carry it for you.’
‘I’ll phone you tomorrow, OK?’ ‘OK, goodbye.’
I’m tired. I think I’ll go to bed early tonight.
It’s a nice day. I think I’ll sit in the garden.
It’s raining. I don’t think I’ll go out.
Do not use the present simple (I go / I phone etc.) in sentences like these:
I’ll phone you tomorrow, OK? (not I phone you)
I think I’ll go to bed early. (not I go to bed)
B. Do not use I’ll … for something you decided before
I’m working tomorrow. (not I’ll work)
There’s a good film on TV tonight. I’m going to watch it. (not I’ll watch)
What are you doing at the weekend? (not What will you do)
→ Units 26–27
C. Shall I … ? Shall we … ?
Shall I answer the phone?
No, it’s OK, I’ll answer it.
Shall I / we … ? = Do you think this is a good thing to do? Do you think this is a good idea?
It’s very warm in this room. Shall I open the window?
‘Shall I phone you this evening?’ ‘Yes, please.’
I’m going to a party tonight. What shall I wear?
It’s a nice day. Shall we go for a walk?
Where shall we go for our holidays this year?
‘Let’s go out this evening.’ ‘OK, what time shall we meet?’
What are you doing tomorrow? → UNIT 26
I’m going to … → UNIT 27
will / shall (1) → UNIT 28