We use the future perfect continuous in two ways.

1. We use it to show that something will continue until a certain time or event in the future. This action or event started in the past and will continue into the future.

• They will have been cooking for 5 hours by the time the guests arrive.
• He is going to have been working every day since last month by the time he finishes the project.

These sentences usually have two time phrases: 1) "for" or "since" 2) by + (time/deadline).

2. We can use the future perfect continuous to show the cause of something in the future.

• He will be tired because he will have been working for 12 hours straight before he comes home.
• They are going to be good at English by next year because they will have been studying for over 2 years in America.

Now, let's take a look at how to make the sentences and questions for the future perfect continuous verb tense. We can use either "will" or "going to".

Here are the two ways that we can make a sentence.

Subject + will have been + present participle…
Subject + be verb + going to have been + present participle…

• She will have been reading for 2 hours by the time Michael gets here.
• Greg will have been working here for 15 years by the time he gets his first promotion.
• I am going to have been waiting for 2 hours before I see the doctor!
• She will be tired because she is going to have been working all day.

We can make a yes/no question like this.

Will + subject + have been + present participle…?
Be Verb + subject + going to have been + present participle…?

• Will you have been living here for 5 years by the time you move back to your home country?
• Is she going to have been here for 2 hours before the doctor even sees her?

We can also use question words. Look at some examples.

• How long will you have been exercising when you finish?
• What will you have been doing for 10 years?

Although this is not the most commonly used verb tense, it is useful to know. So, go to the next lessons and spend a little time studying and becoming more comfortable with the future perfect continuous verb tense. Advanced English grammar points like this are not always common, but they are important to know if you want to speak English fluently or even if you just want to speak English well. You might not always use this grammar point when you speak, but you will need it when reading and listening.