Future Perfect Use

1. The future perfect in Spanish is used the same as in English, to convey an action or a state that will have been done in the future:

• Mañana habré terminado mi novela.
  Tomorrow I will have finished my novel.

• Para el 2150 habremos destruido el planeta.
  By 2150 we will have destroyed the planet.

2. The future perfect can express probability or conjecture in the past (just like the future can express probability or conjecture in the present):

• ¿Qué habrán comido los niños?
  I wonder what the children have eaten / ate.

• Son las 5: papá y mamá ya habrán llegado.
  It’s 5: mom and dad must have arrived by
  now.