Future and conditional of probability (guessing about the present and the past)

Serán las tres.It must be about three o'clock.

Spanish has a second job for its future and conditional tenses: guessing. The speaker is not predicting a future event or imagining something unreal, but saying what is probably true, without being sure. The forms are the ones you already know, and the time the guess refers to decides which one fits.

Quick shortcut: guessing about now = futuro (estará); guessing about something already finished = futuro perfecto (habrá salido); the same two guesses about a past moment = condicional (estaría) and condicional perfecto (habría salido).

The four forms and their time

The future forms look at the guess from the present, and the conditional forms look at it from a moment in the past. That moment is usually named in the sentence or clear from the story.

A guess about now: futuro simple

Futuro simple guesses about what is true at this moment. It is common with verbs that describe states, such as ser, estar, tener or costar, and with ages, times, prices and quantities:

• Estará en casa. (He must be at home.)
• Tendrá unos cuarenta años. (She must be about forty.)
• Costará unos veinte euros. (It probably costs about twenty euros.)
• Serán las tres. (It must be about three o'clock.)

In a question, the same form means "I wonder": ¿Dónde estará Ana? (Where can Ana be?) ¿Qué hora será? (What time can it be?) A guess about the present is not the same as a prediction, though context usually tells them apart: Mañana lloverá (Tomorrow it will rain) looks ahead, while Ahora lloverá en la costa (It must be raining on the coast now) guesses about the present.

Looking ahead: prediction, not a guess

The future tenses also look ahead, but that is a different job. A guess is about a situation that is already true (or already over) and that the speaker cannot check. A prediction is about something that has not happened yet, and futuro simple and futuro perfecto say it in their ordinary way:

• Mañana habrá mucha gente en la playa. (There will be a lot of people at the beach tomorrow.)
• Para el lunes ya habrán terminado. (They will have finished by Monday.)

Both are expectations about the future, not conjectures about the present or past. To soften a prediction, Spanish adds an adverb such as seguramente or probablemente rather than changing the tense.

A guess about something already done: futuro perfecto

When the thing you are guessing about has already happened, use haber in the future + a past participle:

• Habrá salido ya. (He has probably left already.)
• No contesta: se habrá dormido. (He isn't answering: he must have fallen asleep.)
• ¿Qué le habrá pasado? (What can have happened to him?)

A guess about a past moment: condicional simple

Telling a story in the past, you can guess about what was true at that moment with the simple conditional. It has the same shade as futuro simple, but placed in the past:

• Serían las tres cuando llegué. (It was probably about three o'clock when I arrived.)
• Tendría unos treinta años entonces. (He was probably about thirty then.)
• ¿Quién sería a esa hora? (Who could it have been at that hour?)

Compare Eran las tres cuando llegué, with the imperfect: it states the time as a fact. The conditional says the speaker is not sure.

A guess about what came before: condicional perfecto

To guess about something that had already happened before a past moment, use habría + a past participle:

• Cuando lo llamé, ya habría salido. (When I called him, he had probably left already.)
• Se habría olvidado de la cita. (He had probably forgotten about the appointment.)

The same form, a different meaning

The forms above are the same as the ones used for plain predictions and for unreal situations, and context tells them apart. Dijo que llegaría a las tres (He said he would arrive at three) reports a future plan, while Llegaría a las tres, no sé (He probably arrived at three, I'm not sure) is a guess. A time expression that points forward (mañana, dentro de un año) usually signals a prediction; a state in the present or a story in the past usually signals a guess.

Ways to say the same thing

Spanish has other ways to express a probable situation, so the tenses are not the only option:

• Adverbs: A lo mejor está en casa. Seguramente está en casa. (He's probably at home.) These keep the ordinary verb forms.
• Deber de + infinitive: Debe de estar en casa. (He must be at home.) Plain deber + infinitive is also heard for the same job, but deber de keeps it apart from deber meaning obligation.

The tenses sound natural and compact in speech, especially in questions. The adverbs are a good choice in writing or when you want to state your degree of certainty.

Common mistakes

• ❌ Serán las tres cuando llegué. → ✅ Serían las tres cuando llegué. (the guess is about a past moment, so it takes the conditional rather than the future.)
• ❌ Sería las tres. → ✅ Serían las tres. (ser agrees with the hour in the plural, as in son las tres.)
• ❌ Ya habrá salido cuando lo llamé. → ✅ Ya habría salido cuando lo llamé. (the guess is about something before a past moment, so it takes the conditional perfect.)

Quick check

1. Say it as a guess: Probablemente son las cinco ahora.
2. Say it as a guess: Probablemente ya salió. (now, looking back)
3. Say it as a guess: Probablemente eran las doce cuando llegó.
4. Which verb forms fit: ¿Dónde (estar) Ana ahora? and ¿Dónde (estar) Ana ayer a esa hora?
5. Is Dijo que llegaría a las tres a guess or a report of a future plan?

Key takeaways

• Besides predicting and imagining, the future and conditional tenses can guess at what is probably true.
• Guess about now = futuro simple (Estará en casa); about something already finished = futuro perfecto (Habrá salido).
• Guess about a past moment = condicional simple (Serían las tres); about something before it = condicional perfecto (Ya habría salido).
• A plain future prediction (Mañana habrá mucha gente) is a different job from a guess; context, such as a forward-looking time word or a past story, separates a guess from a prediction or a report.
• Adverbs (a lo mejor, seguramente) and deber de + infinitive express the same idea with ordinary verb forms.