Najmodavka kaže da će kaucija biti vraćena kad se iselimo.

Najmodavka means landlady or female landlord / lessor. It is the feminine form of najmodavac.

Croatian often uses different noun forms for male and female people, so if the person renting out the apartment is a woman, najmodavka is the expected word.

Kaže is the 3rd person singular present tense form of kazati or reći, meaning says.

So:

• ja kažem = I say
• ti kažeš = you say
• on/ona kaže = he/she says

Here the subject is najmodavka, so kaže means the landlady says.

Here da introduces a subordinate clause and means that.

So:

• Najmodavka kaže... = The landlady says...
• da će kaucija biti vraćena... = that the deposit will be returned...

In Croatian, da is very commonly used to introduce reported statements, thoughts, wishes, and similar clauses.

Će is the auxiliary used to form the future tense.

In this sentence:

• će biti vraćena = will be returned

Its position is normal for Croatian clitic word order. Short unstressed words like će usually appear near the beginning of the clause, and after da it is very natural to get:

• da će kaucija biti vraćena

not usually:

• da kaucija će biti vraćena

So this is standard Croatian word order.

Because kaucija is the subject of the passive clause.

The sentence says:

• the deposit will be returned

In a passive sentence, the thing affected becomes the grammatical subject, so it stands in the nominative:

• kaucija = nominative

Compare the active version:

• Najmodavka će vratiti kauciju.
• The landlady will return the deposit.

There, kauciju is in the accusative because it is the direct object.

This is a passive construction:

• biti = to be
• vraćena = returned

Together, they mean to be returned.

With će, you get the future passive:

• će biti vraćena = will be returned

So the full idea is not someone will return the deposit but the deposit will be returned.

Because vraćena agrees with kaucija.

Kaucija is:

• feminine
• singular
• nominative

So the passive participle must also be:

• feminine singular nominative → vraćena

Compare:

• novac je vraćen = the money was returned
• pismo je vraćeno = the letter was returned
• kaucija je vraćena = the deposit was returned

This agreement is very important in Croatian.

The verb ending -mo tells you the subject is we.

So:

• iselim = I move out
• iseliš = you move out
• iselimo = we move out

Croatian often leaves subject pronouns unstated because the verb ending already shows who the subject is. That is why there is no separate word for we here.

Because the verb is iseliti se, which means to move out.

The se is part of the verb. In Croatian, many verbs are reflexive or use se as a fixed element.

So:

• iseliti se = to move out
• seliti se = to move / relocate
• useliti se = to move in

You should learn iseliti se as a whole verb, not just iseliti by itself.

Because after time words like kad meaning when, Croatian often uses the present form to refer to a future event.

So:

• kad se iselimo = when we move out / once we have moved out

This is standard Croatian.

Using kad ćemo se iseliti usually sounds like an actual question:

• Kad ćemo se iseliti?
• When will we move out?

So in a time clause, kad se iselimo is the natural choice.

This is connected to how Croatian expresses future events in subordinate clauses.

After conjunctions like:

• kad = when
• ako = if
• čim = as soon as

Croatian commonly uses a present-tense form, often from a perfective verb, to express a future completed event.

Here iselimo comes from the perfective verb iseliti se, so it suggests:

• when we have moved out
• once we move out

That fits the meaning well, because the deposit will be returned only after the moving-out is completed.

Yes, in this sentence they mean the same thing: when.

• kad = shorter, very common in everyday speech
• kada = fuller form, sometimes a little more formal or careful

So both are possible:

• kad se iselimo
• kada se iselimo

In normal conversation, kad is extremely common.

Yes. A more active version would be:

• Najmodavka kaže da će vratiti kauciju kad se iselimo.

That means:

• The landlady says she will return the deposit when we move out.

The original sentence uses the passive:

• da će kaucija biti vraćena

This puts the focus on the deposit rather than on who returns it. Both are natural, but the passive sounds a bit more impersonal and formal.