What will be done by then — and what has probably happened
The futuro perfecto says what will have happened by a future deadline. Form: future of haber + past participle.
habré · habrás · habrá · habremos · habréis · habrán + participio
Para el viernes habré terminado el informe. (By Friday I will have finished the report.)
Same irregular participles as always: hecho, visto, dicho, escrito, puesto, vuelto...
The futuro perfecto loves para + time: "by" a deadline.
Para junio habremos acabado el curso. (By June we will have finished the course.)
Para entonces ya habrán llegado. (By then they will have already arrived.)
para el lunes = by Monday · para entonces = by then · para cuando vuelvas = by the time you return.
Like the simple future, the futuro perfecto also guesses — about the recent past. "He must have..." = habrá + participio.
—Luis no está. —Habrá salido. (Luis isn't here. — He must have gone out.)
¿Dónde habré dejado las llaves? (Where can I have left my keys?)
This is extremely common speech: se habrá olvidado (he must have forgotten), habrán perdido el tren (they must have missed the train).
Choose by asking: finished BEFORE the future moment (perfecto) or happening AT it (simple/continuous)?
A las diez habré cenado. (By ten I will have had dinner — done before.)
A las diez estaré cenando. (At ten I will be having dinner — in progress.)
A las diez cenaré. (At ten I will have dinner — starts then.)
Three futures, three relationships to the clock. Spanish is precise here — and examiners test it.
A typical B1 paragraph about future plans mixes all the future tools.
El año que viene terminaré el máster. Para septiembre habré encontrado trabajo, y dentro de cinco años estaré dirigiendo mi propio equipo.
(Next year I will finish my master's. By September I will have found a job, and in five years I will be leading my own team.)
terminaré (simple) → habré encontrado (perfect) → estaré dirigiendo (continuous). Use all three in your writing for top marks.
Traps for English speakers
These are the errors English speakers make most often.