Using Subjunctive after Conjunctions of Time

The Spanish subjunctive is used in adverb clauses when the action described in the clause is anticipated or hypothetical (a reservation, a condition not yet met, a mere intention). Adverb clauses are sentences that function as adverbs in compound sentences:

Organizaremos una fiesta / cuando mi esposo regrese de su viaje.
We will organize a party / when my husband comes back from his trip.

In the previous example, the main clause is organizaremos una fiesta and its verb (organizaremos) is in the indicative mood, future tense. However, the adverb clause that modifies that verb (in this case, establishing a condition of time for the action to happen) must use regrese, the subjunctive form of the verb regresar (to come back). Adverb clauses like this one are usually introduced by conjunctions, which you can use to identify the type of clause that it's being used. The previous sentence, for example, uses the conjunction cuando (when) to introduce the adverb clause. The word cuando is a conjunction of time, just like después (after). These conjunctions are used with the subjunctive to express anticipated circumstances, that is, a future occurrence not yet met. Let's study some examples from our catalog of authentic videos.

An example with the conjunction cuando (when):

pues no quiere deberle nada a nadie cuando llegue a la presidencia.

because he doesn't want to owe anything to anyone when he reaches the presidency.

Caption 23, Andrés Manuel López Obrador - En campaña
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An example with the conjunction hasta (until), which must be combined with the pronoun que (that):

Yo mantendré esa tradición hasta que me muera.

I will keep this tradition until the day I die.

Caption 66, Estado Falcón - Locos de la Vela
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Here's an example with the conjunction siempre (always), which combined with the pronoun que (that) means "whenever" or "as long as." Pay attention, the word order has been changed, so the main clause appears at the end.

Pero siempre que sea posible,

But whenever it is possible,

recurriremos a un fotógrafo profesional.

we'll turn to a professional photographer.

Caption 27, Raquel y Marisa - Español Para Negocios - Introducción
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Now, that doesn't mean that you should always use subjunctive after conjunctions of time. You must use it only when you are talking about actions anticipated to occur in the future. If, for example, the conjunction is used to introduce an adverb clause that refers to actions in the past or in progress, known facts or habits, you must use the indicative. Let's see examples:

An example where you don't use subjunctive after the conjunction cuando (when):

Lo primero que hago cuando voy de compras

The first thing that I do when I go shopping

es mirar los escaparates.*

is to look at the display windows.

Captions 3-4, Raquel - Haciendo compras
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*Another common word order could be: Lo primero que hago es mirar los escaparates cuando voy de compras.

Now, an example where you don't use subjunctive after hasta que (until):

Hay policías desde que salgo de mi casa hasta que entro al Tec.

There are police from when I leave my house until I enter the Tech.

Caption 67, Alumnos extranjeros del - Tec de Monterrey
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And here's and example with the conjunction siempre (always) combined with the pronoun que (that) that doesn't use subjunctive either.

Entonces, yo siempre que estaba en Lima no los encontraba.*

So, every time I was in Lima, I didn't meet up with them.

Caption 9, Gonzalo el Pintor - Vida
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*Again, the main clause appears at the end of the sentence here, but you can easily change the word order: Entonces, yo no los encontraba siempre que estaba en Lima.

Summarizing: the subjunctive is used after conjunctions of time (such as cuando, hasta que, siempre que, etc.) only when you want to express anticipated circumstances, that is, a future occurrence not yet met (anyway, strictly speaking future is always hypothetical, right?). For your reference, other conjunctions of time that use subjunctive are después de que (after), mientras que (while, as long as), tan pronto que (as soon as), antes de que (before), and en cuanto (as soon as). So remember to always use subjunctive after them if you want to talk about anticipated circumstances. There is only one exception that applies to después de que (after), antes de que (before), and hasta que (until): you can get away with using a verb in infinitive (ending in -ar, -er, -ir) instead of subjunctive if you get rid of the pronoun que (that). Check the following examples: