The future for guesses: Serán las diez

In The simple future (hablaré) and irregular stems you learned the future for things that will happen. Spanish has a second, very common use of the same forms: a guess about the present. English says must be, probably, I suppose, I wonder; Spanish often just uses the future.

A guess about now

Compare a statement of fact with a guess:

• Son las diez. = It's ten o'clock. (I'm looking at my watch.)
• Serán las diez. = It must be about ten. (I'm guessing.)

• Serán las diez más o menos.It must be about ten o'clock.
• Marta no contesta, estará en el gimnasio.Marta isn't answering, she's probably at the gym.
• El nuevo profesor tendrá unos cuarenta años.The new teacher must be about forty.
• Hará unos treinta grados.It must be around thirty degrees.
• Los niños estarán durmiendo ya.The children are probably asleep by now.

Nothing in these sentences refers to the future: the guess is about right now. Context tells you which meaning is intended. Estará en casa can mean she'll be at home (tomorrow) or she's probably at home (now).

Wondering: questions with the future

In a question, the future means I wonder… or Who could…? You are not asking anyone in particular; you are thinking aloud.

• ¿Dónde estará mi móvil?Where can my phone be?
• ¿Quién será a estas horas?Who could that be at this time of night?
• ¿Cuánto costará un piso así?I wonder how much a flat like that costs.

Granting a point: "it may be…, but"

The future followed by pero concedes something before you disagree:

• Será muy famoso, pero no canta bien.He may be very famous, but he can't sing.

Guessing about the past

• For a guess about a past moment, use the conditional (The conditional: politeness, advice, hypotheses): Serían las dos cuando llegó = It must have been about two when he arrived.
• For a guess about something that has just happened, use the future perfect (habrá salido = he must have gone out), covered in Future and conditional perfect, including guesses about the past.

Other ways to guess

The future is the most compact way, but you can also say seguramente, probablemente or a lo mejor + present (A lo mejor está en casa), or deber de + infinitive (Debe de estar en casa). All are used in Spain and Latin America.

Latin America

This use of the future is common everywhere, and in Latin America it is arguably the main use of the simple future in speech, since plans are expressed with ir a. With ustedes: ¿Tendrán hambre? (I wonder if you're hungry / They must be hungry.)

Common mistakes

• Translating must be with tener que: Tiene que ser las diez. For a guess, say Serán las diez or Deben de ser las diez.
• Será las diez: the verb still agrees with las diez, so it is serán, just as son las diez (Telling the time: es la una, son las dos y media).
• Using the future for a guess about the past: Ayer estará enfermo. Use the conditional: Ayer estaría enfermo.
• Reading every future as a prediction: ¿Dónde estará Juan? usually means I wonder where Juan is, not Where will Juan be?