Future Perfect Progressive

The future perfect Progressive (continuous) tense is formed with four verbs: will + have + been + present participle

The first three verbs are always will have been, no matter what the subject is.

What is a present participle?
A present participle is a verb with the –ing ending. For example:

When do we use the future perfect progressive (continuous)?

This tense is not often used in conversation because it is more complex in its structure and function.

First, let me review the future perfect. Remember that the future perfect tense is used to express an action that is not done yet but will be done by a certain point in the future. The future point can be expressed as a time (3:00, Thursday, the end of the summer, next year, etc.) or an action (I reach the airport, we finish the race, he retires, etc.). The perfect action will be completed any time before that point.

• By next summer, I will have saved enough money to buy a new car.
  • I haven’t saved enough money yet, but by next summer (or sooner) I will have enough money.
• By the time I reach the airport, the plane will have already left.
  • The plane will leave sometime before I reach the airport.

In the future perfect continuous, the future perfect activity will be in progress for a duration of time. By using the continuous tense, we emphasize the duration of an activity that happened in a progressive (rather than sudden) way. Therefore, we can only use verbs that express activities taking place over time. For example:

• Working, living, studying, sleeping, thinking, hoping, traveling, saving, etc.

We use the preposition by to express a point in the future (either a time or an action) that allows us to measure the duration of the activity. Usually the by phrase comes first, followed by a comma. Then the independent clause includes the future perfect continuous. The duration of the activity is usually expressed as for + duration of time.

• By 3:00, they will have been studying for four hours.
• By the end of the summer, I will have been saving money for five months.
• By the time we finish the race, we will have been running for two hours.
• By the time he retires, he will have been working for 45 years.

In some cases, the future point expressed with by marks the end of the progressive activity:

• By the time we finish the race, we will have been running for two hours.
  • In this sentence, it is clear that we will stop running when we finish the race.
• By the time he retires, he will have been working for 45 years.
  • In this sentence, it is clear that he will stop working when he retires.

In other cases, the future point express with by does not necessarily indicate that the progressive activity will end at the point. It may just be a convenient point to measure how much time will have passed:

• By 3:00, they will have been studying for four hours.
  • It is possible that they will continue to study after 3:00.
• By the end of the summer, I will have been saving money for five months.
  • It is possible that I will continue to save money after the summer.