Jamstveni rok traje tri godine.

Because Croatian normally expresses this idea with the verb trajati, meaning to last.

So the sentence is structured like:

• Jamstveni rok = the warranty period
• traje = lasts
• tri godine = three years

A literal English version would be The warranty period lasts three years.

Using je here would not sound natural in Croatian.

After the numbers dva/dvije, tri, and četiri, Croatian uses the form godine:

• dvije godine
• tri godine
• četiri godine

But after pet and higher, it changes to godina:

• pet godina
• šest godina
• deset godina

So tri godine is the correct form here.

It is a noun phrase made of:

• jamstveni = an adjective
• rok = a noun

The adjective jamstveni describes the noun rok.

So this is literally something like warranty-related period/term, which in natural English is warranty period.

Because it agrees with rok, which is:

• masculine
• singular
• nominative

In Croatian, adjectives must match the noun they describe in gender, number, and case.

So:

• jamstveni rok = masculine singular
• jamstvena kartica = feminine singular
• jamstveno razdoblje = neuter singular

The ending -i is the correct one for this masculine nominative singular form.

Yes. Rok is a flexible word and can mean:

• deadline
• term
• period
• time limit

Its exact meaning depends on context.

In jamstveni rok, it means period/term, not deadline. So here it refers to the length of time during which the warranty is valid.

Yes, usually.

Jamstvo and expressions built from it, such as jamstveni rok, sound more standard, official, or legal.

In everyday speech, many people also say:

• garancija
• garantni rok in some contexts, though this is less standard

So Jamstveni rok traje tri godine sounds natural and fairly formal, especially in product information, contracts, or official notices.

Because Croatian does not have articles like English a and the.

So jamstveni rok can mean:

• a warranty period
• the warranty period

The exact meaning is understood from context.

That is completely normal in Croatian.

No, Croatian word order is fairly flexible.

Jamstveni rok traje tri godine is the most neutral and natural order.

You could also say:

• Tri godine traje jamstveni rok.

This puts more emphasis on tri godine.

So the original sentence is the standard, neutral version, but other word orders are possible for emphasis or style.

It is in the nominative, because it is the subject of the sentence.

You can identify it as the thing that traje:

• What lasts? → jamstveni rok

So:

• jamstveni = nominative masculine singular
• rok = nominative masculine singular

In this sentence, tri godine expresses duration, and Croatian commonly uses the accusative for duration expressions with verbs like trajati.

For a learner, the most useful thing is to memorize the pattern:

• trajati jedan dan
• trajati dva dana
• trajati tri godine
• trajati pet godina

So even if the detailed grammar around numbers can get complicated, traje tri godine is the normal pattern you should learn.

A few natural alternatives are:

• Jamstvo traje tri godine.
• Jamstvo vrijedi tri godine.

These are very close in meaning.

The original sentence with jamstveni rok is a bit more explicit and formal, because it names the warranty period itself, rather than just saying the warranty.