Obračunsko razdoblje traje mjesec.

It means something like billing period, accounting period, or calculation period, depending on context.

• razdoblje = period
• obračunsko = an adjective meaning related to calculation, billing, settlement, or accounting

So obračunsko razdoblje is a fixed expression for a period used for billing or accounting.

Because it has to agree with razdoblje.

In Croatian, adjectives agree with the noun in:

• gender
• number
• case

Here:

• razdoblje is neuter
• singular
• nominative

So the adjective also takes the neuter singular nominative form:

• masculine: obračunski
• feminine: obračunska
• neuter: obračunsko

That is why we get obračunsko razdoblje.

Traje is the 3rd person singular present tense of the verb trajati, which means to last.

So:

• trajem = I last
• traješ = you last
• traje = he/she/it lasts

Since obračunsko razdoblje is singular, the verb is also singular:

• Obračunsko razdoblje traje... = The billing period lasts...

Because after trajati when you say how long something lasts, Croatian commonly uses the accusative of duration.

Here, mjesec is masculine inanimate, and for masculine inanimate nouns:

• nominative = mjesec
• accusative = mjesec

So the form looks the same.

That is why:

• traje mjesec = it lasts a month

You may also hear:

• traje mjesec dana

This is also very common and often sounds more natural in everyday usage.

It usually means a month, but in practice it can also feel like one month depending on context.

Croatian has no articles, so mjesec can correspond to:

• a month
• the month
• sometimes even one month, if the context makes that clear

In this sentence, the natural English meaning is:

• The billing period lasts one month or
• The billing period lasts a month

Because Croatian does not have articles.

English uses:

• a month
• the billing period

Croatian simply says:

• obračunsko razdoblje
• mjesec

Whether something is a, the, or sometimes just a general idea is understood from context.

It is not necessarily better, but it is very common and often sounds a bit more natural when talking about duration.

Compare:

• traje mjesec = lasts a month
• traje mjesec dana = lasts a month

Both are correct.
The version with dana is a very common Croatian way to express duration.

You will often hear:

• dva dana
• tjedan dana
• mjesec dana
• godinu dana

So mjesec dana is a very useful pattern to remember.

Yes, Croatian word order is more flexible than English, but not every version sounds equally natural.

The neutral, standard order here is:

• Obračunsko razdoblje traje mjesec.

You could also rearrange words for emphasis, but the original sentence is the most straightforward.

For learners, it is best to remember this pattern:

• [subject] + [verb] + [duration]

So:

• Obračunsko razdoblje
  • traje
    • mjesec

Yes, razdoblje is a normal word meaning period. In formal or administrative language, it is very common.

Depending on context, Croatian might also use:

• period
• rok
• vrijeme

But they are not always interchangeable.

For this sentence, obračunsko razdoblje is the natural formal expression for billing/accounting period.

A rough pronunciation guide is:

• Obračunsko ≈ o-bra-CHOON-sko
• razdoblje ≈ RAZ-dob-lye
• traje ≈ TRA-ye
• mjesec ≈ MYE-se-ts

A few helpful notes:

• č sounds like ch in chocolate
• j sounds like English y
• lj is a single soft sound, roughly like ly

So the full sentence sounds roughly like:

o-bra-CHOON-sko RAZ-dob-lye TRA-ye MYE-se-ts

Yes, it sounds fairly formal or administrative.

That is mainly because of:

• obračunsko razdoblje — a technical/formal phrase
• the overall structure, which sounds like something from a contract, invoice, policy, or official document

In everyday casual speech, people might choose simpler wording if the context allows it, but in business or official Croatian this sentence is perfectly natural.