Although the question wordA word that introduces a wh-question. E.g.: What are you doing? since when is normally used with the present perfectThe aspect expressing completion. E.g.: He’s finished university., with present simple it expresses annoyance.

Since when are people like Geoffrey allowed to join this club?!

The future simple tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses. is used in complex sentences (referring to future timeA concept which is related to our perception of reality; that part of existence which is measured in seconds, minutes, hours, days, weeks, etc.) which contain clauseA group of related words containing a subject and a verb.s of condition, time or purpose.

If you have finished, then we'll go.
When you finish, we'll go.
I'm taking this book with myself, so that I'll have something to read on the train.

We use the future simple tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses. to express a subjective prediction, which is a hypothesis based on opinion or intuition. Whether or not the eventA general term expressing that somebody or something does something or that something happens. E.g.: An apple fell on Isaac’s head. will happen or not is not certain. Very often this kind of prediction is introduced by I think/I don't think.

The future simple can be used for future plans that have just been decided; that is, they are unpremeditated.

We can use the present simple tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses. for future eventA general term expressing that somebody or something does something or that something happens. E.g.: An apple fell on Isaac’s head.s which we cannot control.

Her mother retires in 2 years.
Christmas Eve is on a Tuesday this year.
Next week he has his operation, then he goes on holiday.
The last plane to Zuerich leaves at 20.20.

StateA condition that exists at a particular time. E.g.: I am sick. This melon weighs two kilos. verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis.s

State verbs express states or conditions which are relatively static. They include verbs of perception, cognition, the senses, emotion and state of being:

The auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") DO for emphasisSpecial importance or attention given to something. E.g.: All I wanna do is have some fun. in present simple

In present simple we can use the auxiliary do/does in affirmativeA declarative sentence indicating "yes"; also called a positive sentence. E.g.: John likes squash a lot. sentences to express emphasis. In such a case the infinitive form of the verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis. is used. In speech the auxiliary is stressed.