Ik zet de televisie af voordat ik ga slapen.

Because the full verb is afzetten, which is a separable verb in Dutch.

• Infinitive: afzetten
• Main clause: Ik zet de televisie af

In a normal main clause, the conjugated part goes in the usual verb position, and the separable prefix moves to the end.

Compare:

• Ik zet de televisie af.
• Hij zet de radio af.

But in places where the verb stays together, you get:

• Ik wil de televisie afzetten.
• Omdat ik de televisie afzet...

This is a very common Dutch pattern.

In this sentence, afzetten means to turn off.

Even though the parts can look literal, separable verbs often have meanings that are partly idiomatic. So here:

• de televisie afzetten = to turn the television off

A useful note: in Netherlandic Dutch, many speakers more often say de televisie uitzetten for turn off the TV.
Afzetten is also common in Belgian Dutch. So the sentence is correct, but depending on region, uitzetten may sound more natural.

Because televisie is a de-word in Dutch.

So you say:

• de televisie
• de tv

There is no strong logic you can always rely on for noun gender in Dutch, so this is something you usually have to learn with each noun.

Dutch normally needs an article here because you are talking about a specific object: the television.

So:

• Ik zet de televisie af = I turn off the television

Without the article, it sounds incomplete or unnatural in standard Dutch.

Voordat means before when it introduces a whole clause.

So:

• voordat ik ga slapen = before I go to sleep

Use voordat when before is followed by a subject + verb.

Compare:

• voordat ik ga slapen = before I go to sleep
• voor het slapen = before sleeping / before sleep

So voordat is the right choice because it introduces the clause ik ga slapen.

After voordat, you are in a subordinate clause, and Dutch often sends verbs toward the end of the clause.

In this sentence:

• voordat ik ga slapen

Both ga and slapen belong to the verb phrase. In modern Dutch, ga slapen is the normal order here.

You may sometimes see other verb orders in Dutch subordinate clauses, but for this kind of everyday sentence, voordat ik ga slapen is the natural version learners should use.

Because gaan slapen means to go to sleep or to go to bed to sleep, which matches the idea of what you do before bedtime.

• voordat ik ga slapen = before I go to sleep / before I go to bed

If you said voordat ik slaap, that would mean something more like before I am asleep or before I sleep, which is less natural in this situation.

So gaan slapen is the idiomatic choice.

Because after gaan used like this, Dutch does not use te.

So you say:

• Ik ga slapen.
• Ik ga werken.
• Ik ga eten.

Not:

• Ik ga te slapen. ❌

This is a common pattern: gaan + infinitive.

It is in the present tense:

• ik zet
• ik ga

Dutch often uses the present tense for:

• habits and routines
• general truths
• near future

So this sentence can mean something like:

• I turn off the television before I go to sleep
• I turn off the television before going to bed

It sounds like a regular habit.

Yes, absolutely.

That version is very natural too:

• Voordat ik ga slapen, zet ik de televisie af.

When the subordinate clause comes first, the main clause follows the normal Dutch inversion rule, so you get:

• ..., zet ik ... not
• ..., ik zet ...

So both are correct:

• Ik zet de televisie af voordat ik ga slapen.
• Voordat ik ga slapen, zet ik de televisie af.

Both are correct.

• de televisie is a bit more formal or full
• de tv is very common in everyday speech

So many people would naturally say:

• Ik zet de tv af voordat ik ga slapen.

That sounds very normal.

Yes, in many contexts you can.

For many Dutch speakers, especially in the Netherlands, de televisie uitzetten is the more common way to say turn off the television.

So you may hear:

• Ik zet de televisie uit voordat ik ga slapen.

That means the same thing here.

Very roughly:

• uitzetten = very common for switching devices off
• afzetten = also possible, and especially common in Belgian Dutch

So if you are learning standard everyday Dutch for broad use, uitzetten is worth knowing well.

Yes. In everyday Dutch, you can replace it with hem or the reduced spoken form 'm.

For example:

• Ik zet hem af voordat ik ga slapen.
• Ik zet 'm af voordat ik ga slapen.

Because televisie is a de-word, the pronoun is hem in this kind of sentence.

The reduced form 'm is very common in speech.

Most naturally, it sounds like a habit or regular routine.

• Ik zet de televisie af voordat ik ga slapen.

That suggests something like I turn off the TV before I go to sleep as a usual thing.

But depending on context, present tense in Dutch can also refer to a near-future event. For example, if someone asks what you do tonight, this sentence could also describe tonight’s plan.

So the form is the same; context tells you whether it is habitual or future.