Roen i sindet kommer tilbage, når jeg ved, at alt er klart.

Ro is the base form of the noun, while roen is the definite singular form, literally the calm/the peace.

In Danish, abstract ideas are often expressed with the definite form where English might use a more general phrase. So roen i sindet is a natural way to say peace of mind.

Literally, i sindet means in the mind or in the spirit.

But sind is not exactly the same as brain. It refers more to a person’s inner mental or emotional state. In this sentence, roen i sindet is an idiomatic expression meaning something like inner calm or peace of mind.

Because the normal expression is ro i sindet, with the definite form sindet.

The noun sind is a neuter noun:

• indefinite: et sind
• definite: sindet

Even when English would not use the, Danish often does in fixed expressions like this. So i sindet sounds natural, while i sind would sound unusual here.

Kommer tilbage is the verb komme plus the particle tilbage, and together they mean come back or return.

So:

• komme = come
• komme tilbage = come back / return

This is very common in Danish. You could also say vender tilbage, which is a bit more formal or literary.

Use når when something happens when/whenever a condition is met, especially if it is expected, repeated, or seen as natural.

Use hvis for if, when the condition is more uncertain.

So here:

• når jeg ved, at alt er klart = when I know that everything is clear
• It suggests a regular or expected connection: peace of mind returns whenever that is the case.

If you said hvis jeg ved..., it would sound more like a hypothetical condition.

Because Danish separates two kinds of to know:

• at vide = to know a fact
• at kende = to know a person, place, or something through familiarity

Here the speaker knows that everything is clear, which is factual knowledge, so ved is correct.

Examples:

• Jeg ved, at han kommer. = I know that he is coming.
• Jeg kender ham. = I know him.

At introduces a clause meaning that:

• jeg ved, at alt er klart = I know that everything is clear

This is very common after verbs like vide, tro, sige, and mene.

In spoken Danish, at is sometimes omitted, but learners should usually keep it because it is clear and standard.

Because klart agrees with alt.

Alt means everything, and grammatically it behaves like a neuter singular word. So the adjective must also be neuter singular:

• alt er klart = everything is clear

Compare:

• døren er klar if you had a common-gender singular noun
• huset er klart with a neuter singular noun
• tingene er klare with a plural noun

Because når and at both introduce subordinate clauses.

In Danish subordinate clauses, the subject normally comes before the finite verb:

• jeg ved
• alt er klart

A useful extra point: if there were an adverb like ikke, it would usually come before the verb in a subordinate clause:

• når jeg ikke ved det
• at alt ikke er klart

That is different from main clause word order, where the verb usually comes earlier because of the V2 rule.

These commas mark subordinate clauses.

In Danish, some writers use start commas before subordinate clauses, as in this sentence:

• Roen i sindet kommer tilbage, når jeg ved, at alt er klart.

In modern Danish, those commas are often optional, depending on comma style. So you may also see:

• Roen i sindet kommer tilbage når jeg ved at alt er klart.

Both styles can be correct if used consistently.

Yes. That is completely natural.

It means the same thing, but the sentence starts with the subordinate clause. When a non-subject element comes first in a Danish main clause, the finite verb must come before the subject in the main clause:

• Når jeg ved, at alt er klart, kommer roen i sindet tilbage.

Notice:

• kommer comes before roen

This is a classic Danish V2 pattern.

Because it describes a general relationship, not just one single event.

• kommer tilbage
• jeg ved
• alt er klart

This makes the sentence sound like a general truth: whenever this situation exists, peace of mind returns.

Also, Danish often uses the present tense after når, even when English might think in more future-like terms. That is normal Danish usage.