Celkový počet je důležitý.

Because celkový is an adjective, and it has to agree with počet in gender, number, and case.

Here, počet is:

• masculine
• singular
• nominative

So the adjective also appears in the masculine singular nominative form: celkový.

If the noun changed, the adjective would change too:

• celkový počet = total number/count
• celková suma = total sum
• celkové množství = total amount

Počet is a masculine inanimate noun.

A learner often has to memorize gender along with the noun, but the ending can sometimes help. Nouns ending in a consonant are often masculine, and počet fits that pattern.

In this sentence, you can also see it from agreement:

• celkový has a masculine singular form
• důležitý also has a masculine singular form

Both match počet.

Because důležitý is describing the subject počet.

Even though in English we say is important, in Czech the adjective after je still agrees with the subject:

• Celkový počet je důležitý.

So důležitý must also be:

• masculine
• singular
• nominative

Compare:

• Počet je důležitý. = The number is important.
• Suma je důležitá. = The sum is important.
• Množství je důležité. = The amount is important.

In standard Czech, je is normally required here.

So:

• Celkový počet je důležitý. = correct

Unlike some Slavic languages, Czech usually does not omit the present tense of být (to be) in this kind of sentence.

Leaving it out would sound incomplete or nonstandard in ordinary Czech:

• Celkový počet důležitý. = not standard

The main words here are in the nominative because počet is the subject of the sentence.

Breakdown:

• celkový — nominative singular masculine
• počet — nominative singular
• je — verb
• důležitý — nominative singular masculine, agreeing with the subject

This is a very common pattern in Czech:

[subject in nominative] + [form of být] + [adjective agreeing with the subject]

Most often, počet means number or count.

In this sentence, English translations like these are natural:

• The total number is important.
• The total count is important.

Which English word sounds best depends on context:

• počet studentů = number of students
• počet bodů = number of points
• počet případů = number of cases

It usually refers to something countable, so number/count is often better than amount.

Because Czech has no articles like English a/an/the.

So Celkový počet je důležitý can mean:

• The total number is important
• or sometimes A total number is important, depending on context

Usually the context tells you which English article is appropriate.

This is normal in Czech:

• Student přišel. = The student came / A student came
• Kniha je nová. = The book is new / A book is new

Yes, Czech word order is more flexible than English, but the basic version here is the most neutral:

• Celkový počet je důležitý.

You might also see:

• Důležitý je celkový počet.

That version puts more emphasis on důležitý or contrasts the idea with something else, like:

• Nezáleží na jednotlivých číslech. Důležitý je celkový počet. = The individual numbers don’t matter. What is important is the total number.

So the original word order is the normal, neutral one.

Roughly: doo-leh-zhi-tee

A few helpful points:

• ů is pronounced like a long ú
• ž sounds like the s in measure
• í is a long ee sound
• Czech stress is usually on the first syllable

So:

• DŮ-le-ži-tý

The same first-syllable stress rule applies to the whole sentence:

• CEL-ko-vý PO-čet je DŮ-le-ži-tý

They are related, but they are different parts of speech.

• celkový = total, overall → adjective
• celkem = altogether, in total, overall → adverb

In your sentence, celkový is correct because it modifies the noun počet:

• celkový počet = total number

But celkem is used differently:

• Celkem je to drahé. = Overall, it is expensive.
• Celkem pět lidí přišlo. = Altogether five people came.

So you would not normally say celkem počet.

You make it negative by changing je to není:

• Celkový počet není důležitý. = The total number is not important.

The adjective důležitý does not change just because the sentence is negative. The negation is carried by the verb:

• je = is
• není = is not

Usually no, not if you mean total number.

• celkový počet = total number / overall count
• celý = whole, entire

So celý počet would not normally be the natural way to express total number in Czech.

A useful contrast:

• celkový počet studentů = the total number of students
• celý den = the whole day
• celá kniha = the whole book

So celkový is the right adjective here.