The future perfect is used to denote:
1) an action viewed as completed by a definite future moment or before another future action: My sister will have left school by July.
2) (with statal verbs) an action lasting over a certain period of time up to the given future moment: Kate will have been a student for half a year by March.
The Future Perfect Continuous
Formation. The future perfect continuous is formed analytically by means of the auxiliary to be in the future perfect (shall/will have been) and participle I of the notional verb.
Main Uses. The future perfect continuous denotes an action lasting for a period of time up to or including a certain future moment. This moment can be indicated by an adverbial with the preposition by or by another future action. The Future Perfect Continuous is normally used to emphasize the process rather than the future result. E.g. By the end of the year, they’ll have been working at this project for two years.
