Future Perfect Tense expresses an activity that will be completed before another time or event in the future. By the time introduces a time clauses; the simple present is used in a time clause.
(+) S + SHALL/WILL + HAVE + V-3 + O
(- ) S + SHALL/WILL + NOT + HAVE + V-3 + O
(?) SHALL/WILL + S + HAVE + V-3 + O
USE 1 Completed Action Before Something in the Future
The Future Perfect expresses the idea that something will occur before another action in the future. It can also show that something will happen before a specific time in the future.
• By next November, I will have received my promotion.
• By the time he gets home, she is going to have cleaned the entire house.
• I am not going to have finished this test by 3 o’clock.
• Will she have learned enough Chinese to communicate before she moves to Beijing?
• Sam is probably going to have completed the proposal by the time he leaves this afternoon.
• By the time I finish this course, I will have taken ten tests.
• How many countries are you going to have visited by the time you turn 50?
Notice in the examples above that the reference points (marked in italics) are in Simple Present rather than Simple Future. This is because the interruptions are in time clauses, and you cannot use future tenses in time clauses.
USE 2 Duration Before Something in the Future (Non-Continuous Verbs)
With Non- Continuous verbs and some non-continuous uses of Mixed verbs, we use the Future Perfect to show that something will continue up until another action in the future.
• I will have been in London for six months by the time I leave.
• By Monday, Susan is going to have had my book for a week.
Although the above use of Future Perfect is normally limited to Non-Continuous Verbs and non-continuous uses of Mixed Verbs, the words “live,” “work,” “teach,” and “study” are sometimes used in this way even though they are NOT Non-Continuous Verbs.
REMEMBER No Future in Time Clauses
Like all future forms, the Future Perfect cannot be used in clauses beginning with time expressions such as: when, while, before, after, by the time, as soon as, if, unless, etc. Instead of Future Perfect, Present Perfect is used.
• I am going to see a movie when I will have finished my homework. Not Correct
• I am going to see a movie when I have finished my homework. Correct
The examples below show the placement for grammar adverbs such as: always, only, never, ever, still, just, etc.
• You will only have learned a few words.
• Will you only have learned a few words?
• You are only going to have learned a few words.
• Are you only going to have learned a few words?
• Change the following sentences into positive, negative, and interrogative forms of Future Perfect.
1. The office boy (clean) the classroom by the time in the students start the lesson tomorrow morning.
2. By the end of this month the police (proceed) this case for one year.
3. They (do) their homework by the time the teacher arrives in the classroom tomorrow morning.
4. The students (practice) singing for thirty minutes when I come at nine o’clock tomorrow morning.
5. The train (leave) by the time they get to the railway station at 5.oo p.m tomorrow.
• Complete this sentence with the future perfect tense.
1. They (arrive) by the time you go home.
2. By the time you come back, we (do) it.
3. We (complete) the project by the end of this year.
4. In three months’ time she will (be) married.
5. By this time tomorrow I (finish) the work.