We use the future perfect continuous tense to:

1. say how long an event will have been happening when another event will happen.
2. give a reason for something in the future.

How to Make the Future Perfect Continuous

will have been …ing (+ (time))

Examples of the future perfect continuous

1.
By the end of this year, he will have been studying Korean for 6 months.
By this time next week, we will have been dating for a month.

2.
He will be tired when he comes home because he will have been running.
She will be angry because she will have been answering phone calls all day.

Exercises

1. Choose a time in the future, and say how long you will have been doing it.
2. Pick a feeling you will have in the future, and explain why you will be feeling that way.