How do I use cuando with the subjunctive?

Grammar Genius,

Why do I say ¨Cuando vuelve¨ if there isn´t any doubt about my returning?

First off, the subjunctive is not always used in situations of doubt. In fact, it is very common to use the subjunctive when there is ZERO doubt.

'Cuando' along with other similar words such as 'hasta que' and 'tan pronto como' belong to a group of subordinators (words that link two clauses together) called 'time subordinators.'

Whenever these time subordinators point to an event that is or was in the future, it takes the subjunctive. In fact, it is incorrect to use the future or conditional tense in a subordinate phrase.

For example, the following phrases are INCORRECT:

Cuando volveré a mi pais, sabré más español.
Me dijo que se lo prestaría cuando terminaría.

Taking into account the above mentioned rule, write in the correct form of the verb see answers):

Cuando______a mi pais, sabré más español.
Me dijo que se lo prestaría cuando ______.

NOTE: it is OK to use the future and conditional in questions. Cuándo volverás? Cuándo tendría yo una oportunidad como ésa?

To test your understanding, read the below examples and explain why example A uses the subjunctive and Example B does not. Click on the sentences to check you answer:

A. Cuando regrese a los Estados Unidos, tengo que conseguir un trabajo.	When I return to the United States, I have to get a job.
B. Tenía que conseguir trabajo cuando regresé a los Estados Unidos.	I had to get a job when I returned to the United States.

A. Mi hermano siempre me pega hasta que grito ´uncle.´	My brother always hits me until I yell ´uncle.´
B. Mi hermano seguirá pegandome hasta que grite ´uncle.´	My brother will continue hittting me until I yell uncle.

Below is a list of the most common time subordinators:

Después de que Luego de que	After
Desde que	Since
Siempre que	Every time
A pocas días de que	A few days after
Hasta que	Until
Apenas Nomás que En cuanto Tan pronto como Una vez que Nada más	As soon as
Cuando	When
Mientras que	As long as
A medida que  Según Conforme	As

NOTES:

Antes de que (before): Subjunctive is ALWAYS used because it must always refer to a future event.

Mientras (while): When refering to completed actions in the past or present it takes the indicative. But, when it refers to simultaneous events in the future either the subjunctive or the indicative may be used:

La próxima semana mientras yo limpio / limpie la casa puedes preparar la comida.

Next week while I clean the house, you can prepare the food.

To test your understanding, fill in the blanks:

Lo hice antes de que me lo (mandar)______.
Lo haré antes de que me lo (pedir)_____.