The future perfect continuous tense is formed with the future perfect tense of the verb to be (shall/will have been) + a present participle (verb + -ing), as follow:

Example: My uncle will have been working in Antarctica for exactly ten years next Sunday.

 

The future perfect continuous tense is used:

  • to indicate the length of time that an action continues in the future.

Example: At noon tomorrow, my aunt will have been driving a hearse for fifteen years.

  • to show an action in progress until an event happens in the future. Here, we usually make use of the time clause. The future perfect continuous tense may come either before or after the time clause.

a) By the time the bus arrives, we will have been waiting for more than thirty minutes.
b) We will have been waiting for more than thirty minutes by the time the bus arrives,
Time clause: by the time the bus arrives
Main clause: we will have been waiting 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).