The future perfect tense is used to describe an action that will be completed at a specific time in the future. For example:

• “I will have finished my homework by the time the movie starts.” (In this sentence, the action of “finishing my homework” will be completed before the movie starts.)

The future perfect continuous tense, on the other hand, is used to describe an action that will have been in progress for a certain amount of time in the future. For example:

• “I will have been working on this project for three weeks by the time the deadline arrives.” (In this sentence, the action of “working on this project” will have been ongoing for three weeks by the time the deadline arrives.)

In summary, the future perfect tense is used to describe a completed action in the future, while the future perfect continuous tense is used to describe an ongoing action that will have been in progress for a certain amount of time in the future.