Nedoplatek je vysoký.

• nedoplatek = a noun
• je = the 3rd person singular of být (to be), so is
• vysoký = an adjective, here meaning high

So the sentence structure is very straightforward:

noun + is + adjective

Because it agrees with nedoplatek.

In Czech, adjectives must match the noun they describe in:

• gender
• number
• case

Nedoplatek is:

• masculine inanimate
• singular
• nominative

So the adjective also has to be:

• masculine inanimate
• singular
• nominative

That gives the form vysoký.

If the noun were different, the adjective would change too. For example:

• částka je vysoká = the amount is high
  because částka is feminine
• nájemné je vysoké = the rent is high
  because nájemné is neuter

Because it is the subject of the sentence.

In Nedoplatek je vysoký, the sentence says something about the underpayment / outstanding amount, so that noun is the subject, and subjects are normally in the nominative.

Also, after být (to be), the adjective vysoký is also in the nominative here, because it is a predicate adjective describing the subject.

Yes. Czech often uses vysoký in the same way English uses high for amounts, prices, fees, bills, or balances.

So in this sentence, vysoký is very natural.

Typical examples:

• vysoká cena = a high price
• vysoký účet = a high bill
• vysoký nedoplatek = a high outstanding balance / underpayment

English learners sometimes wonder if velký (big) would work. Sometimes it might be understood, but vysoký is the normal choice for amounts and levels.

Nedoplatek is a noun meaning something like:

• underpayment
• outstanding balance
• amount still owed
• arrears in some contexts

It is commonly used for things like:

• utility bills
• rent or service charges
• tax statements
• insurance payments

It refers to the amount that still has to be paid because what was paid before was not enough.

A useful contrast:

• přeplatek = overpayment, money paid too much
• nedoplatek = underpayment, money still owed

The neutral, standard word order is:

Nedoplatek je vysoký.

That is the most natural way to present new information.

Czech word order is more flexible than English, so other orders are possible, but they usually sound marked or put emphasis somewhere else. For example:

• Vysoký je nedoplatek.
  This is possible, but it sounds unusual without a special context.
• Je vysoký nedoplatek.
  This can work in some contexts, but it no longer feels like the same simple neutral statement.

So for a learner, the best default is: subject + je + adjective

Because Czech has no articles.

English distinguishes:

• a high underpayment
• the underpayment is high

Czech does not use words equivalent to a/an/the in normal grammar. The listener understands from context whether the noun is general, specific, known, new, and so on.

So Nedoplatek je vysoký can be translated into English in different ways depending on context, even though Czech uses no article.

A simple pronunciation guide:

• Nedoplatek ≈ NE-do-pla-tek
• je ≈ ye
• vysoký ≈ VI-so-kee

A few key points:

• Czech stress is usually on the first syllable of each word:
  • NEdoplatek
  • JE
  • VYsoký
• j in Czech is pronounced like English y in yes
• ý is a long vowel, so the last syllable of vysoký is held a bit longer

A rough full pronunciation: NE-do-pla-tek ye VI-so-kee

In standard Czech, yes.

Je is the present-tense form of být (to be) for he/she/it and also for singular nouns like nedoplatek.

So:

• Nedoplatek je vysoký. = correct
• Nedoplatek vysoký. = not standard as a normal full sentence

In some informal styles, especially headlines or notes, Czech may omit forms of to be, but learners should definitely use je in ordinary sentences like this.

You simply negate je:

• Nedoplatek je vysoký. = The underpayment is high.
• Nedoplatek není vysoký. = The underpayment is not high.

Here:

• není = is not

That is the normal way to negate this sentence.

Yes. In speech, Czech often makes a yes/no question mainly by intonation:

• Nedoplatek je vysoký. = statement
• Nedoplatek je vysoký? = Is the underpayment high?

You can also use question words in other contexts, but for a simple yes/no question, intonation is often enough.

Czech does not need the English-style word order change:

• English: Is the underpayment high?
• Czech: still Nedoplatek je vysoký?

Yes, nedoplatek is masculine inanimate.

One clue is its dictionary form ending:

• -ek often appears in masculine nouns

Also, its adjective agreement confirms it:

• nedoplatek je vysoký
  The adjective form vysoký is masculine singular nominative

It is specifically masculine inanimate, not animate, because it is a thing, not a person or animal.

The dictionary forms are:

• nedoplatek → already in dictionary form
• být → the infinitive of je
• vysoký → already in dictionary form

So if you were looking them up, you would search for:

• nedoplatek
• být
• vysoký

This is useful because Czech verbs and adjectives often appear in sentences in changed forms, but dictionaries list the base form.