The future perfect tense is formed by using the simple future tense of the verb to have (will have) + the past participle of the main verb. It is used for an action which will have finished by some future time or date as mentioned:
Statement: She will have sewn the patch on her jeans by nine o'clock
Question: Will the people have put out the fire by the time the firemen arrive?
The future perfect tense is used:
- to show that an activity will be completed by a specified time in the future.
Example: I will have saved about one million dollars by the year 2090.
- to show that an action will be completed before another takes place in the future.
Example: The fire will have burnt the building to the ground by the time the firemen arrive.
- to show a situation will be over in the future.
Example: The special offer – buy two, get one free – will have finished by midday tomorrow.
Example: If you don't hurry up, we will have eaten all the food when you get to the table.
- with time clause. The future perfect tense may come either before or after the time clause.
a) On April 1st, she will have been here for six months.
b) She will have been here for six months on April 1st.
c) We will have waited for more than thirty minutes by the time the bus arrives,
Time clauses: On April 1st/by the time the bus arrives
Main clauses: She will have been here for six months/We will have waited for more than thirty minutes
A comma is placed at the end of a time clause when the time clause comes before the main clause as in (a).
- with time expressions such as by seven o'clock, by this evening, by next Thursday, by then, until noon tomorrow, before closing date.
Example: He will have prepared the documents by next Friday.
The future perfect tense and the future perfect continuous tense
a) When Joan competes in the marathon next week, she will have trained for nine months.
b) When Joan competes in the marathon next week, she will have been training for nine months.
Both (a) and (b) have the same meaning.