Ugovorna kazna je visoka.

Because ugovorna is an adjective that agrees with kazna in gender, number, and case.

Here, kazna is:

• feminine
• singular
• nominative

So the adjective also takes the feminine singular nominative form:

• ugovorni = masculine
• ugovorna = feminine
• ugovorno = neuter

Since kazna is feminine, you say ugovorna kazna.

For the same reason: visoka must agree with kazna.

Even though visoka comes after je and works like high in The contractual penalty is high, it still agrees with the noun:

• kazna je visoka = the penalty is high
• trošak je visok = the cost is high
• more je visoko would be wrong, because more is neuter; you would need visoko

So visoka is the feminine singular form.

Je is the 3rd person singular present tense of biti = to be.

So:

• je = is

In this sentence:

• Ugovorna kazna je visoka.
• The contractual penalty is high.

This is the normal Croatian equivalent of English is.

Normally, no. In standard Croatian, the present tense of to be is usually expressed, unlike in some other Slavic languages.

So you say:

• Ugovorna kazna je visoka.

Not normally:

• Ugovorna kazna visoka.

You may sometimes see omissions in headlines, notes, or very elliptical style, but in ordinary full sentences, je should be there.

It is in the nominative singular.

Why? Because kazna is the subject of the sentence, and subjects are normally in the nominative.

Also, this is the dictionary form of the noun:

• kazna = penalty, punishment

So in this sentence:

• ugovorna kazna = the contractual penalty
• subject = nominative singular

Yes, very often it is used as a legal or business term.

It literally means something like:

• contractual penalty
• penalty specified by a contract

The adjective ugovorna comes from ugovor = contract, agreement.

So learners should understand ugovorna kazna as a common noun phrase, not just two random words put together.

Because Croatian does not have articles like English a/an/the.

So:

• kazna can mean a penalty or the penalty
• ugovorna kazna can mean a contractual penalty or the contractual penalty

Which one is meant depends on context.

That is very normal in Croatian, and English speakers often need time to get used to it.

Yes. Ugovorna kazna je visoka is the most neutral, standard word order.

It follows the basic pattern:

• subject + je + adjective/complement

Croatian word order is more flexible than English, but changing it usually changes the emphasis.

For example:

• Ugovorna kazna je visoka. = neutral
• Visoka je ugovorna kazna. = more marked; emphasis on visoka
• Kazna je visoka. = possible if ugovorna is already understood or unnecessary

So the original sentence is the safest and most natural form for a learner to use.

A simple learner-friendly pronunciation guide would be:

• Ugovorna ≈ oo-go-VOR-na
• kazna ≈ KAZ-na
• je ≈ ye
• visoka ≈ vee-SO-ka

A few helpful notes:

• j in Croatian is like English y in yes
• z is a voiced z
• Croatian spelling is quite phonetic, so words are usually pronounced much as they are written

Yes, it is normal.

Croatian often uses visok / visoka / visoko metaphorically for amounts, prices, penalties, costs, and similar things, just like English uses high.

So:

• visoka kazna = a high penalty / a large fine
• visoka cijena = a high price
• visok trošak = a high cost

So visoka is the natural adjective here.

The correct form here is ugovorna, from ugovor = contract.

A common learner issue is accidentally guessing the adjective form. Croatian adjective formation is not always fully predictable from English, so it is best to learn common adjective pairs as vocabulary:

• ugovor = contract
• ugovorni / ugovorna / ugovorno = contractual, contract-related

So in this sentence:

• ugovorna kazna = contractual penalty

You make it negative by changing je to nije:

• Ugovorna kazna nije visoka.
• The contractual penalty is not high.

This is very useful to learn early:

• je = is
• nije = is not

Yes, grammatically you could, but it means something slightly different in focus.

• Ugovorna kazna je visoka.
  This treats ugovorna kazna as one noun phrase: the contractual penalty.

• Kazna je ugovorna i visoka.
  This says: The penalty is contractual and high.
  Here ugovorna and visoka are both predicates describing kazna.

So if you mean the standard legal term contractual penalty, the original sentence is better.