The future perfect continuous is used to express the duration of an action up to a future point in time. This tense is not commonly used in English.
This tense is often used with the following time expressions:
... by / ... by the time ...
Basic Construction
Positive
Subject + will + have + been + verb + ing + object(s) + time Expression
We will have been studying for two hours by the time he arrives.
Negative
Subject + will not (won't) + have + been + verb + ing + object(s) + time Expression
He won't have been working long by two o'clock.
Question
(Question Word) + will + subject + have + been + verb + ing + object(s) + time Expression
How long will you have been working on that project by the time he arrives?
