Most commonly the future perfect is used with a time marker that indicates by when (i.e. prior to what point in time) the event is to occur, as in the previous examples. However it is also possible for it to be accompanied by a marker of the retrospective time of occurrence, as in "I will have done it on the previous Tuesday". This is in contrast to the present perfect, which is not normally used with a marker of past time: one would not say *"I have done it last Tuesday", since the inclusion of the past time marker last Tuesday would entail the use of the simple past rather than the present perfect.
The English future perfect places the action relative only to the absolute future reference point, without specifying the location in time relative to the present. In most cases the action will be in the future relative to the present, but this is not necessarily the case: for example, "If it rains tomorrow, we will have worked in vain yesterday."[1]
The future perfect construction with will (like other constructions with that auxiliary) is sometimes used to refer to a confidently assumed present situation rather than a future situation, as in "He will have woken up by now."
The time of perspective of the English future perfect can be shifted from the present to the past by replacing will with its past tense form would, thus effectively creating a "past of the future of the past" construction in which the indicated event or situation occurs before a time that occurs after the past time of perspective: In 1982, I knew that by 1986 I would have already gone to prison. This construction is identical to the English conditional perfect construction.
An obsolete term found in old grammars for the English future perfect is the "second future tense."[2][3]
For more information, see the sections on the future perfect and future perfect progressive in the article on uses of English verb forms.