The future perfect tense in English isn’t very common, but it is useful in some situations, and it’s very important to understand it when you hear it. it’s easy to get confused with all the different auxiliary verbs.
Also it’s good to listen to how to pronounce it – as this tense has so many auxiliary verbs, we usually shorten it when we speak.
We use this English verb tense:
With a future time word, ( and often with ‘by’) to talk about an action that will finish before a certain time in the future, but we don’t know exactly when.
By 10 o’clock I will have finished my homework. (=I will finish my homework some time before 10, but we don’t know exactly when)
By the time I’m sixty, I will have retired. (= I will retire sometime before I’m sixty. We don’t know exactly when, but definitely before my sixtieth birthday)
As the future perfect continuous, but with stative verbs.