Future perfect and the conditional of probability

What it is

Spanish can turn a tense into a guess. You already know the future of probability: ¿Dónde estará Ana? —Estará en el trabajo (I suppose she's at work). This topic takes the same idea into the past.

The future perfect (futuro compuesto: habrá salido) has two jobs. It says that something will be finished before a point in the future (Para el viernes ya habré terminado), and, much more often in conversation, it makes a guess about something that has already happened (No contesta: habrá salido, "she must have gone out"). The conditional (condicional: serían, tendría) and the conditional perfect (habría salido) make guesses about the past. Finally, deber de + infinitive expresses the same probability with a verb instead of a tense: Debe de estar cansada.

How to form it

The future perfect is the future of haber plus a past participle. The participle never changes: ella habrá salido, ellos habrán salido.

The conditional perfect works the same way with habría, habrías, habría, habríamos, habrían. Irregular participles stay irregular: hecho, dicho, visto, puesto, vuelto, roto, escrito, abierto. Object and reflexive pronouns go before haber: se habrá ido, lo habrán cancelado.

For probability, think of a shift of one step: to guess, you move the verb one tense "forward" from the tense you would use if you were sure.

When to use it

• Completion before a future point, usually with para + a time, ya or cuando: Para diciembre habremos ahorrado lo suficiente. Cuando vuelvas, ya habré limpiado la cocina.
• Guesses about the recent past, often from visible evidence: Hay charcos en el patio: habrá llovido. Se habrá olvidado de la cita.
• Wondering questions about something already done: ¿Quién habrá dejado la puerta abierta? ¿Dónde habré puesto los lentes? ("where can I have put…")
• Guesses about the past with the conditional, especially time, age, quantity and reasons: Cuando me llamó serían las once. Tendría unos treinta años. Lo diría en broma (he was probably joking).
• Guesses about an earlier past with the conditional perfect, when the story is already in the past: Cuando llegamos, el tren ya habría salido, porque el andén estaba vacío.
• deber de + infinitive says the same: Debe de estar cansada. Deben de haber salido ya. Debió de perder el bus.

• Para diciembre habremos ahorrado lo suficiente para el viaje.We will have saved enough for the trip by December.completion
• Hay charcos en el patio: habrá llovido.There are puddles in the yard: it must have rained.guess about the recent past
• Cuando me llamó serían las once.It must have been about eleven when she called me.guess about the past
• Debe de estar cansada después del viaje.She must be tired after the trip.deber de

Contrasts and traps

• Probability, not future. In No contesta: habrá salido, nothing lies in the future: the speaker is guessing about now. Translate it as "must have", "probably" or "I guess".
• A past guess takes the conditional. ✗ Ayer estará cansado mixes a past time marker with a present guess: Ayer estaría cansado.
• deber or deber de? Debes descansar = you have to rest (obligation). Debe de estar cansado = he must be tired (probability). In real speech Debe estar cansado is very common for probability and is accepted; the norm prefers deber de there. The reverse, ✗ Debes de descansar for an obligation, counts as a mistake.
• No future perfect after cuando. In time clauses about the future, use the present perfect subjunctive: Cuando hayas terminado, avísame (never ✗ cuando habrás terminado).
• Latin American speech. In everyday talk the future perfect of completion often gives way to the preterite or ir a: Cuando vengas, ya lo terminé, Para el lunes ya lo voy a tener listo. Recognise these; use habré terminado when you write. For guesses, seguro que or a lo mejor + indicative are just as common: Seguro que salió.

If you speak Portuguese

Portuguese usually guesses with dever: deve ter saído, devia ser tarde, devia ter uns vinte anos. Spanish can do the same, but its compound forms use haber, never tener: debe de haber salido (✗ debe tener salido). Very often a plain tense is more natural: habrá salido, sería tarde, tendría unos veinte años. Portuguese terá saído matches habrá salido exactly, but it is rare in Brazilian speech, so it won't come to mind on its own: practise it on purpose.