Hvis jeg drikker kaffe, sover jeg ikke godt i nat.

Hvis means if and introduces a condition.

So Hvis jeg drikker kaffe means If I drink coffee.

Danish often distinguishes:

• hvis = if (a condition)
• når = when (something expected, repeated, or treated as a fact)

In this sentence, the idea is conditional: coffee leads to poor sleep. So hvis is the natural choice.

Compare:

• Hvis jeg drikker kaffe, sover jeg ikke godt i nat.
  If I drink coffee, I won’t sleep well tonight.

• Når jeg drikker kaffe, sover jeg ikke godt om natten.
  When I drink coffee, I don’t sleep well at night.
  This sounds more like a repeated pattern or general truth.

Also, om usually means whether in this kind of context, so you would not use om here.

That is very normal in Danish.

Danish often uses the present tense to talk about the future when the time is clear from context or from a time expression like i nat.

So:

• drikker = present tense
• sover = present tense
• i nat tells you the situation is about tonight, so the future meaning is clear

A natural English translation might use will, but Danish often does not need it.

So Hvis jeg drikker kaffe, sover jeg ikke godt i nat is perfectly normal Danish.

You could make the future more explicit in other ways, but the simple present is the most straightforward and natural here.

This is because Danish is a V2 language. That means the finite verb usually comes in the second position in a main clause.

In this sentence, the first part is a subordinate clause:

• Hvis jeg drikker kaffe

That whole clause takes the first slot. Then the main clause starts, and its finite verb must come next:

• sover jeg ikke godt i nat

So the structure is:

• [Hvis jeg drikker kaffe], [sover] [jeg] [ikke godt i nat].

If the main clause came first, you would get normal subject-verb order:

• Jeg sover ikke godt i nat, hvis jeg drikker kaffe.

So sover jeg is not random; it is required by Danish word order after an opening clause.

In a Danish main clause, ikke usually comes after the finite verb and the subject, and before other elements such as adverbs or objects.

Here the main clause is:

• sover jeg ikke godt i nat

So the order is:

• sover = finite verb
• jeg = subject
• ikke = negation
• godt i nat = the rest

If there were no inversion, the normal order would be:

• Jeg sover ikke godt i nat.

A useful contrast:

• Main clause: Jeg drikker ikke kaffe.
• Subordinate clause: hvis jeg ikke drikker kaffe

In subordinate clauses, ikke often comes earlier, before the finite verb. But in this sentence, ikke is in the main clause, so its position is different.

Because godt is the form used here adverbially.

The base adjective is:

• god = good

But after verbs like sove, Danish uses the -t form to describe how something happens:

• sove godt = sleep well
• synge godt = sing well

So:

• Jeg sover godt = I sleep well
• Jeg sover ikke godt = I don’t sleep well

Even though godt looks like the neuter form of god, in sentences like this it functions like an adverb in English.

So god would be wrong here.

I nat is a fixed time expression meaning tonight or during the night, depending on context.

In this sentence, it means tonight.

Danish often uses short fixed expressions for time without an article, for example:

• i dag = today
• i morgen = tomorrow
• i går = yesterday
• i nat = tonight

So you should learn i nat as a set phrase.

Also note the difference between:

• i nat = tonight / during this night
• om natten = at night / during the night in general

So if you wanted a more general meaning, you might say:

• Når jeg drikker kaffe, sover jeg ikke godt om natten.

Yes, you can.

That version is also grammatical:

• Jeg sover ikke godt i nat, hvis jeg drikker kaffe.

The meaning is basically the same. The difference is mostly about focus and word order.

When the sentence starts with the if-clause:

• Hvis jeg drikker kaffe, sover jeg ikke godt i nat.

the condition is introduced first.

When the sentence starts with the main clause:

• Jeg sover ikke godt i nat, hvis jeg drikker kaffe.

the main point comes first, and the condition is added afterward.

Notice the word order change:

• after the opening hvis clause: sover jeg
• when the sentence starts with jeg: jeg sover

So this is a good example of how Danish word order changes depending on what comes first.

Because Hvis jeg drikker kaffe is a subordinate clause, and it is followed by the main clause.

In standard written Danish, a subordinate clause placed before the main clause is separated by a comma:

• Hvis jeg drikker kaffe, sover jeg ikke godt i nat.

So the comma shows the boundary between:

• the condition: Hvis jeg drikker kaffe
• the main statement: sover jeg ikke godt i nat

It helps the reader see the structure clearly.