Unit 25. When I do / When I've done

A : What time will you phone me tomorrow?
B : I'll phone you when I get home form work.

'I'll phone you when I get home from work' is a sentence with two parts
   → I'll phone you
   → when I get home from work (tomorrow)
The time in the sentence is future ('tomorrow') but we use a present tense (get) in the when-part of the sentence.

The same thing happens after : while    before    after    as soon as    until

• I'm going to read a lot of books while I'm on holiday.
• I'm going back home on Sunday. Before I go, I'd like to visit the museum.
• Wait here until I come back.

You can also use the present perfect (have done) after when / after / until / as soon as

• Can I borrow that book when you've finished it?
• Don't say anything while Ian is here. Wait until he has gone.

It is often possible to use the present simple or the present perfect:

• I'll come as soon as I finish. or I'll come as soon as I've finished.
• You'll feel better after you have something to eat. or You'll feel better after you've had something to eat.

But do not use the present perfect if two things happen together. The present perfect shows that one thing will be complete before the other (so the two things do not happen together).

• When I've phoned Kate, we can have dinner.
  ( = First I'll phone Kate and after that we can have dinner. )
• When I phone Kate this evening, I'll invite her to the party. (not 'when I've phoned')
  ( In this example, the two things happen together. )