Here's one of the classic traps for English speakers: in Spanish, after time conjunctions like cuando ("when"), hasta que ("until"), and similar, you do not use the future tense — even though English uses "will" in the same spot. Spanish uses the subjunctive instead.
The English Pattern You Have to Unlearn
In English, a sentence like "When he arrives, I'll tell him" uses arrives (present) in the first clause and will tell in the main clause. Spanish does something different: it uses the present subjunctive in the cuando-clause.
Cuando venga, le diré.
When he comes, I will tell him.
Do not say "Cuando vendrá, le diré". That's grammatically incorrect in Spanish, even though it looks like a natural literal translation.
Time Conjunctions That Trigger the Subjunctive
When these conjunctions refer to a future event, they require the subjunctive:
| Conjunction | Meaning |
|---|---|
| cuando | when |
| hasta que | until |
| en cuanto | as soon as |
| tan pronto como | as soon as |
| después (de) que | after |
| antes (de) que | before (always subjunctive) |
| mientras | while / as long as |
| una vez que | once |
Examples in Action
Cuando llegues a casa, llámame.
When you get home, call me.
Voy a esperar hasta que termines.
I'm going to wait until you finish.
En cuanto sepa algo, te aviso.
As soon as I know something, I'll let you know.
Tan pronto como abran la tienda, entraremos.
As soon as they open the store, we'll go in.
Después de que hablen con el jefe, podrán salir.
After they speak with the boss, they'll be able to leave.
Why Not the Future?
Spanish treats events in temporal clauses as hypothetical until they actually happen. Even if you're sure the person will arrive, from a grammatical standpoint the arrival is an "unrealized" event. The subjunctive is the mood for unrealized, wished-for, or uncertain events — so it's the correct fit.
Meanwhile, the main clause (what you'll do once the event happens) can use the future tense, ir + a, an imperative, or any other form that makes sense.
Iremos al parque cuando deje de llover.
We'll go to the park when it stops raining.
Vamos a salir en cuanto llegue Pedro.
We're going to leave as soon as Pedro arrives.
Llámame cuando estés lista.
Call me when you're ready.
The Important Exception: Past or Habitual Events
When these same conjunctions refer to something that already happened or happens habitually, use the indicative, not the subjunctive. The subjunctive only applies to unrealized, future actions.
Cuando llegué a casa, ella ya estaba dormida.
When I arrived home, she was already asleep. (past — indicative)
Cuando llueve, no salgo.
When it rains, I don't go out. (habitual — indicative)
Cuando llueva mañana, no saldré.
When it rains tomorrow, I won't go out. (future — subjunctive)
Quick Reference Chart
| Time reference | Mood in cuando-clause | Example |
|---|---|---|
| Future | Subjunctive | cuando llegue |
| Habitual | Indicative | cuando llega |
| Past | Indicative | cuando llegó |
Antes de que Is Always Subjunctive
One conjunction that is always followed by the subjunctive, regardless of time, is antes de que ("before"). Future, past, habitual — it doesn't matter.
Termina tu tarea antes de que lleguen los invitados.
Finish your homework before the guests arrive.
Salí antes de que empezara a llover.
I left before it started raining.
This isn't quite the same rule, but it's worth knowing: antes de que never takes the indicative.
Next up, learn how to talk about things that will already have happened: the future perfect tense.
Related Topics
- Simple Future: Regular FormationB1 — Learn to form the regular simple future in Spanish by adding one set of endings to the infinitive.
- Future Tense: Predictions, Plans, and PromisesB1 — Discover the main uses of the Spanish simple future — forecasts, promises, and scheduled events.
- Ir + A + InfinitiveA2 — Use the ir + a + infinitive construction to talk about near or planned future actions in everyday speech.