Kasno je, zato idemo kući.

Because Croatian often uses the verb biti (to be) in statements about time, weather, and general conditions.

So:

• Kasno je = It is late

Even though English needs a dummy subject it, Croatian does not use an equivalent subject here. The je is simply the 3rd person singular form of biti.

Compare:

• Hladno je. = It is cold.
• Vruće je. = It is hot.
• Rano je. = It is early.

Croatian says the condition directly, without a separate word for it.

Croatian usually does not use a subject pronoun in expressions like this.

English says:

• It is late

Croatian says:

• Kasno je

The subject is understood from the context and the verb form. In impersonal expressions like this, no actual subject needs to be stated.

This is very common in Croatian.

Here, kasno is being used predicatively, meaning it describes a general situation or condition: late.

In this sentence, it functions much like an adverbial/predicative expression in English it is late.

You will also see related forms:

• kasan = late (masculine adjective)
• kasna = late (feminine adjective)
• kasno = late (neuter form / adverb-like use in expressions such as Kasno je)

So in Kasno je, you should learn it as the standard way to say It’s late.

Here zato means therefore, so, or that’s why.

In the sentence:

• Kasno je, zato idemo kući.
• It’s late, so we’re going home.

It connects a reason and a result:

• reason: Kasno je = It’s late
• result: zato idemo kući = so/therefore we’re going home

A very common pattern is:

• ..., zato ... = ..., so/therefore ...

Not always exactly, but in many contexts it works like so or therefore.

Zato often sounds a bit like for that reason or that is why. It clearly points to a consequence.

For example:

• Umoran sam, zato idem spavati.
  I’m tired, so I’m going to sleep.

In everyday Croatian, you may also hear other connectors depending on style and nuance, but zato is a very common and natural choice when one fact leads to another.

Because Croatian usually drops subject pronouns when they are not needed.

The verb idemo already tells you the subject is we, because it is the 1st person plural form of ići (to go).

So:

• idemo = we go / we are going

Adding mi is possible, but it is usually only used for emphasis or contrast:

• Mi idemo kući, a oni ostaju.
  We are going home, but they are staying.

Without emphasis, idemo alone is normal.

Croatian present tense often covers both:

• we go
• we are going

So idemo can mean either, depending on context.

In this sentence, the natural English translation is often:

• We’re going home

because it describes a current decision/action. But grammatically, Croatian simply uses the present tense idemo.

The basic verb is ići, meaning to go.

Its present tense forms are irregular, so they do not all look very close to ići. For example:

• idem = I go / I’m going
• ideš = you go
• ide = he/she/it goes
• idemo = we go
• idete = you (plural/formal) go
• idu = they go

So idemo is simply the we form of ići.

Because kući is the form used after verbs of motion when it means home.

• kuća = house (dictionary form, nominative)
• kući = home / to the house (a directional form)

So:

• Idemo kući. = We’re going home.

This is a very common fixed usage in Croatian.

Historically and grammatically, it is related to that idea, but in modern Croatian, in sentences like this, it usually just means home.

So although you can think of it as a directional form, the natural translation is:

• Idemo kući. = We’re going home.

Learners should usually memorize ići kući as a common expression meaning to go home.

Yes.

• kuća literally means house
• dom can mean home, but often in a more formal, institutional, or emotional sense depending on context

In everyday speech, when talking about going home, Croatian very commonly uses kući:

• Idem kući. = I’m going home.

So in this sentence, kući is exactly what you would expect.

Because the sentence has two clauses:

• Kasno je
• zato idemo kući

The comma helps separate the reason from the result. This is normal punctuation in Croatian when clauses are linked in this way.

So the comma here works similarly to English punctuation in:

• It’s late, so we’re going home.

Yes, Croatian word order is flexible, though some versions sound more natural than others depending on emphasis.

The original:

• Kasno je, zato idemo kući.

is neutral and natural.

You could also hear something like:

• Zato idemo kući jer je kasno.

But that changes the structure a bit to something like:

• That’s why we’re going home, because it’s late.

Croatian word order often changes for focus, rhythm, or style, but the original sentence is a very standard way to say it.

Yes, absolutely.

Kasno je is a complete sentence by itself and is very commonly used in everyday speech.

For example:

• Moramo krenuti. Kasno je.
  We have to leave. It’s late.

So in your example, the first clause already makes full sense on its own, and the second clause explains the consequence.

It is neutral and natural. You can use it in both everyday conversation and normal written Croatian.

Nothing in the sentence is especially slangy, overly formal, or unusual. It is a very standard sentence structure.

You would change the verb form from idemo (we go) to idem (I go):

• Kasno je, zato idem kući.

Other person changes would work the same way:

• Kasno je, zato ideš kući. = It’s late, so you’re going home.
• Kasno je, zato idu kući. = It’s late, so they’re going home.

This is a good sentence pattern to practice with different verb forms.