Future Perfect Tense is used to express an action which, the speaker assumes, will have completed or occurred in the future. It gives a sense of completion of a task that will happen in the future. When we use this tense we are projecting ourselves forward into the future and looking back at an action that will be completed some time later than now. It is most often used with a time expression.
The future perfect is composed of two elements
the simple future of the verb "to have" (will have) + the past participle of the main verb
|+ will have
|+ past participle of the main verb
e.g. The patient will have recovered from illness by the next month.
- I will have been here for six months on June 23rd.
- By the time you read this I will have left.
- You will have finished your report by this time next week.
- Won't they have arrived by 5:00?
- Will you have eaten when I pick you up?
We use the future perfect form when we look back to the past from a point in the future. We usually use a time phrase, for example by tomorrow, for three years:
Do you think she’ll have seen the doctor by four o’clock?
Next month my parents will have been together for thirty years.
At the end of this month, they will have been in their house for one year.
Next month I will have worked for the company for six years.
I think they’ll have got there by six o’clock.
Won’t she have retired by the end of the year? (more common than Will she not have retired?)