The future perfect continuous tense is a verb tense that shows that an action will continue up until a point in the future. It is used to describe an ongoing or incomplete action that will be happening before another action or event in the future. The future perfect continuous is formed using the future perfect of the auxiliary verb to be and the present participle of the main verb.

I will have been studying for hours by the time I finish my exams. (The action of studying will start in the past and continue up until the time when I finish my exams in the future.)

She will have been working on that project for weeks before she presents it to the team. (The action of working on the project will start in the past and continue up until the time when she presents it to the team in the future.)

#1. The Future Perfect Continuous is formed by means of the Future Perfect of the auxiliary verb to be and Participle I of the notional verb.

#2. In the interrogative form, the first auxiliary verb is placed before the subject. And in the negative form, the negative particle not is placed after the first auxiliary verb.

#3. The contracted affirmative forms are:

I’ll have been working
He’ll have been working

The contracted negative forms are:

I shan’t have been working
He won’t have been working

#4. The negative-interrogative forms are:

Will he not have been working? = Won’t he have been working?
Shall we not have been working? = Shan’t we have been working?

The future perfect continuous is used to describe an action that will begin before a definite moment in the future, will continue up to that moment and will be going on at that moment.

We shall have been working at this problem for a month when you visit us a second time.