Future Perfect use
Future Perfect Tense is used in the following situations:
1. When we talk about a situation or an activity which will finish by certain moment in the future.
He will have done the housework by 3 o'clock.
He will have saved enough money for a new car by then.
I hope I will have learnt all the irregular verbs before the exam.
He will have arrived in London in two hours.
2. When we talk about an activity which will last for some period of time until a certain moment in the future.
We will have lived in London for ten years in 2015.
By the time you finish school I will have taught English for 25 years.
Next Monday they will have known each other for 5 months.