Zúčtovací období je jeden rok.

Je is the 3rd person singular present form of být = to be.

So the sentence has the basic pattern:

Zúčtovací období + je + jeden rok
subject + is + predicate

A very literal structure is:

The accounting/billing period is one year.

Because období is singular here, the verb is singular: je.

Here it is singular.

A useful thing to know is that období has the same form in nominative singular and nominative plural:

• to období = that period
• ta období = those periods

So you often tell singular vs. plural from the verb or the context:

• Zúčtovací období je... = singular
• Zúčtovací období jsou... = plural

In your sentence, je shows that zúčtovací období is singular.

Zúčtovací is an adjective modifying období, so it must agree with the noun in gender, number, and case.

However, adjectives of this type often have the same nominative singular form for masculine, feminine, and neuter nouns:

• zúčtovací účet
• zúčtovací operace
• zúčtovací období

So even though období is neuter, zúčtovací does not visibly change here.

In other cases, though, you would see different forms, for example:

• bez zúčtovacího období = without an accounting period

So yes, the adjective is agreeing with the noun; it just happens that this particular form looks the same.

Jeden means one.

In this sentence, jeden rok makes the duration/value explicit: one year.

In Czech, adding jeden can sound a bit more precise or formal, which fits technical or legal language well. A text like this often wants to define something exactly.

If you removed jeden, the sentence Zúčtovací období je rok would be understandable, but it sounds less natural in this kind of definition. Czech usually prefers the numeral when giving an exact measure like this.

So jeden rok is the normal choice here.

Because after jeden, the noun stays in the singular:

• jeden rok = one year
• dva roky = two years
• pět let = five years

So:

• rok is the correct form after jeden
• roku is a different case form, not needed here
• let is used with higher numbers like pět, šest, etc.

This is one of the important Czech number patterns to learn:

• 1
  • singular
• 2–4
  • a different plural form
• 5+
  • genitive plural

Here rok is in the nominative singular.

With být in a sentence like this, Czech often uses the nominative for the predicate noun:

• Petr je učitel
• To je problém
• Zúčtovací období je jeden rok

So both the subject and the predicate expression are in nominative here.

That is different from some other verbs, where Czech may use another case, for example:

• stal se učitelem = he became a teacher

But with plain je in this sentence, jeden rok is nominative.

Because Czech has no articles.

English says:

• the accounting period
• an accounting period
• one year

Czech usually just uses the noun by itself and lets context do the job:

• zúčtovací období
• rok

If Czech wants to emphasize one, it can use jeden, as in this sentence. But jeden is a numeral, not an article.

So English articles are one of the things you simply do not translate directly into Czech.

Czech word order is fairly flexible, but the neutral order here is:

Zúčtovací období je jeden rok.

That sounds like a normal definition.

You can change the order, but then the emphasis changes. For example, putting jeden rok earlier would sound marked or contrastive in most contexts.

In technical or legal writing, Czech often prefers a straightforward, neutral order like the one in your sentence.

Also, in everyday Czech, a speaker might choose a different verb if they want to stress duration:

• Zúčtovací období trvá jeden rok. = The accounting period lasts one year.

But your sentence is perfectly good as a formal definition.

Czech stress is normally on the first syllable of each word:

• ZÚčtovací
• OBdobí
• JE
• JEden
• ROK

A rough pronunciation guide:

• zúčtovací ≈ ZOOCH-toh-vah-tsee
• období ≈ OB-doh-bee
• je ≈ ye
• jeden ≈ YEH-den
• rok ≈ rok

A couple of useful sound notes:

• ů in zúčtovací is a long ú sound
• č sounds like ch in church
• í is a long ee

So the whole sentence is roughly:

ZOOCH-toh-vah-tsee OB-doh-bee ye YEH-den rok

That is only approximate, but it is a helpful starting point.

Yes, it is natural, especially in formal, administrative, financial, or legal language.

A native speaker might also say:

• Zúčtovací období trvá jeden rok.
• Délka zúčtovacího období je jeden rok.

Those versions focus more directly on duration. But your original sentence is completely normal if the goal is to define what the accounting period is.

So the sentence sounds especially appropriate in official or technical text.