Future Perfect

The future perfect tense is formed with the future of haben or sein, and the past participle.

The future perfect deals with the future as if it were already past time (he will have done it), or it is used to imply probability (that was probably him.)  The latter case commonly uses the past tense in English though.

Examples: 

Ø  Er wird gegangen sein.  English: He will have gone.

Ø  Ich werde es genommen haben.  English: I will have taken it.

Ø  Es wird dunkel geworden sein.  English: It will have become dark.

Ø  Das wird Rudi gewesen sein.  English: That will have been Rudi. / That was probably Rudi.

When using modals, the future perfect tense can create the double infinitive construction, so make sure to put the double infinitive at the very end.

Example:

Ø  Die Uhr wird sehr viel gekostet haben müssen.