1. Use and meaning

We use the future perfect continuous to talk about the​​ duration​​ of an activity or event.

It is usually necessary to mention​​ a time reference.

 She​​ will have been​​ working​​ for this company​​ for 6 years​​ in August.

 I​​ will have been studying​​ Spanish​​ for ten years.

2. With for

We usually use ‘for’ to express the​​ duration​​ of a future activity.

 She​​ will have been living​​ abroad​​ for 3 years​​ by the end of next months.

 They​​ will have been seeing​​ each other​​ for 2 months.

3. An activity leading up to a future time

We use the future perfect continuous to describe​​ an activity which leads up to another​​ future activity.

 When you arrive, I​​ will have been cooking​​ for hours.

 She​​ will be tired when you see her because she​​ will have been working​​ hard.