Future Perfect Continuous has two different forms: "will have been doing " and "be going to have been doing." Unlike Future Simple forms, Future Perfect Continuous forms are usually interchangeable.
‘will have been + present participle’
You will have been waiting for more than two hours when she finally arrives.
Will you have been waiting for more than two hours when she finally arrives?
You will not have been waiting for more than two hours when she arrives.
‘am/is/are + going to have been + present participle’
You are going to have been waiting for more than two hours when she finally arrives.
Are you going to have been waiting for more than two hours when she finally arrives?
You are not going to have been waiting for more than two hours she plane finally arrives.
It is possible to use either "will" or "be going to" to create the Future Perfect Continuous with little or no difference in meaning.
We use the Future Perfect Continuous to show that something will continue up until a particular event or time in the future. "For five minutes," "for two weeks," and "since Friday" are all durations which can be used with the Future Perfect Continuous. Notice that this is related to all the perfect continuous forms; however, with Future Perfect Continuous, the duration stops at or before a reference point in the future.
They will have been talking for over an hour by the time Danny arrives.
She is going to have been working at that company for three years when it finally closes.
Peter will have been teaching at the university for more than a year by the time he leaves for Japan.
How long will you have been studying when you graduate?
We are going to have been driving for over three days straight when we get to Las Vegas.
Notice in the examples above that the reference points are in the Present Simple rather than the Future Simple. This is because these future events are in time clauses, and you cannot use future tenses in time clauses.
Using the Future Perfect Continuous before another action in the future is a good way to show cause and effect.
Simon will be tired when he gets home because he will have been running for over an hour.
Maria's English will be perfect when she returns to Germany because she is going to have been studying English in the United Kingdom for over two years.
If you do not include a duration such as "for five minutes," "for two weeks" or "since Friday," many English speakers choose to use the Future Continuous rather than the Future Perfect Continuous. Be careful because this can change the meaning of the sentence. Future Continuous emphasizes interrupted actions, whereas Future Perfect Continuous emphasizes a duration of time before something in the future. Study the examples below to understand the difference.
He will be tired because he will be exercising so hard.
This sentence emphasizes that he will be tired because he will be exercising at that exact moment in the future.
He will be tired because he will have been exercising so hard.
This sentence emphasizes that he will be tired because he will have been exercising for a period of time. It is possible that he will still be exercising at that moment OR that he will just have finished.
Lesson by Tristan, teacher at EC Malta English school
Now complete the following using the correct form:
