We use Future Perfect Continuous Tense to convey,
that an action is going on and will complete a particular period until a particular event or time in future.
Let us see how….
I will have been teaching in ABC School for twenty years, when I retire. This sentence tells us two things, I am teaching in ABC School and I will complete twenty years of teaching by the time I retire.
My daughter will have been working in the hospital for five years, when she turns thirty. This means, My daughter works in a hospital and She will complete five years of service on her thirtieth birthday.
Next year, we will have been taking care of the mentally challenged adults for ten years, at Ashray. This means, 1. We take care of the mentally challenged adults, and 2. We will complete ten years of our service next year.
So basically Future Perfect Continuous Tense tells us that, 1. A person is doing something , and 2. The person will complete a particular period, doing the same, in a specified time in future.
Here are some more examples. Next month, I will have been writing posts for my website for an year. In a few minutes, my friends will have been playing cricket for an hour. At 6, we will have been studying in the library for three hours. After ten minutes, you will have been been talking over the phone for three hours. At the end of this program, she will have been watching television for almost a whole day. This year, he will have been driving a car for twenty five years.
Notice the verbs in the sentences. will have been teaching, will have been working, will have been taking, will have been writing, will have been reading, will have been playing, will have been studying, will have been talking, will have been watching and will have been driving. They all are in Future Perfect Continuous Tense.
All you have to remember is use will have been + ing form of verb with I, You, We, They, He, She and it.
Isn’t it simple? Now try to make as many sentences as possible in future perfect continuous tense so that you will get familiar with this tense and will be able to use it whenever necessary.