We use the perfective will have when we are looking back from a point in time when something will have happened.
By the end of the decade scientists will have discovered a cure for influenza.
I will phone at six o’clock. He will have got home by then.
or looking "back" from the present:
Look at the time. The match will have started.
It’s half past five. Dad will have finished work.
We use would have as the past tense form of will have:
I phoned at six o’clock. I knew he would have got home by then.
It was half past five. Dad would have finished work.