Future Perfect

How to build it

• Affirmative: will have + past participle: She will have written the letter by Friday. Short form: I’ll have, she’ll have.
• Negative: won’t have + past participle: They won’t have finished by then.
• Question: Will + subject + have + past participle: Will you have finished by six?

When to use it

• An action that will be completed before a certain moment in the future, usually with by (by Monday, by then, by the time…): By the end of the year, we’ll have saved enough for a car.
• Looking back from a future point at a total so far: Next month, I’ll have worked here for ten years.
• Confident assumptions about the past or present: Don’t call now, she’ll have gone to bed.

Examples

• I’ll have read the book by the time the film comes out.
• By 2030, they will have built a new bridge.
• Will you have finished the report by tomorrow morning?
• She won’t have arrived yet — her train is late.
• By the time you get here, we’ll have eaten everything.

Common mistakes

• Using the Future Simple with by: I will finish it by Friday is fine as a promise, but to say it’ll already be done at that point use I’ll have finished it by Friday.
• Mixing up by and until: by Friday = not later than Friday; until Friday = all the time up to Friday. I’ll have finished by Friday, but I’ll be busy until Friday.
• will in time clauses: By the time you will come, I will have left → By the time you come, I’ll have left.
• Wrong participle: will have wrote / will have went → will have written / will have gone.

The passive

will + have + been + V3: The letter will have been written. Used mainly in formal writing, plans and reports: By the end of the month, all the applications will have been processed. The bridge will have been completed by 2030.