Future Perfect

We use the Future Perfect to show completed action before something in the future or
that something will continue up until another action in the future.
I will have finished by 4 pm.
I will have worked for an hour when you come.

Future Perfect has two different forms: „will have done“ and „be going to have done.“
Unlike Simple Future forms, Future Perfect forms are usually interchangeable.
FORM Future Perfect with „Will“

[will have + past participle]

Examples:

You will have perfected your English by the time you come back from the U.S.
Will you have perfected your English by the time…?
You will not have perfected your English by the time…

FORM – Future Perfect with „Be Going To“

[am/is/are + going to have + past participle]

Examples:
You are going to have perfected your English by the time you come back from the U.S.
Are you going to have perfected your English by the time …?
You are not going to have perfected your English by the time …

NOTE: It is possible to use either „will“ or „be going to“
to create the Future Perfect with little or no difference in meaning.