Future Perfect Continuous or Progressive Tense expresses the action that will be continuing in the future for a set amount of time that the speaker is sure of. The common backstory here would be the speaker posits themselves in the future and foretells something that is bound to continue happening for a certain period of time in the foreseeable future. "Will have been" is the marker of Future Perfect Continuous Tense while the "for/since + time frame" at the end is the exclusive marker for all perfect continuous tenses.

Structure: 

Subject + will + have + been + verb + ing . . . . . . … + for/since + time frame

Examples:

  • He will have been running on the treadmill for one hour tomorrow.
  • We will have been basking in the afternoon sun for the whole winter.
  • I will have been touring the Australian terrains since next year.
  • Will you have been staring at the moon for one whole hour? 

Note: There is close to no practical use of this Future Perfect Continuous tense in the English language unless the period mentioned covers sometime in the past, the present and the future. 

Future perfect continuous tense is normally used to stress the fact that something has been going on for a long time and it will continue till a particular point in time in the future. It requires pointing out the exact time in the future it will carry on until and for how long it will have been going on in total. 

Examples: 

  • Next month, we will have been living in this house for 10 years.
  • This Friday, I will have been working in the neighborhood for over 30 years.
  • Next Thursday, he will have been roaming the streets homeless for two long years.
  • This year, Helen will have been looking for a perfect care facility for herself for three years.
  • Tomorrow, Jill's father will have been going door to door as a salesman for several months.