Overnattingsutgiften er høy.

Because Norwegian normally writes compound nouns as one word.

Here, overnattingsutgiften is built from:

• overnatting = overnight stay / accommodation
• utgift = expense, cost
• -en = the definite ending, like the

So Norwegian prefers overnattingsutgift where English would often use several words, such as accommodation expense or lodging cost.

Writing it as separate words would usually be wrong in Norwegian.

That -s- is a linking sound/letter used in many Norwegian compounds. It is often called a linking s.

So:

• overnatting
• • utgift
• becomes overnattingsutgift

It does not add a separate meaning by itself. It just helps connect the parts of the compound in a natural way.

Not all compounds use this -s-, so this is something learners mostly have to get used to through exposure.

Because Norwegian often puts definiteness at the end of the noun instead of using a separate word before it.

So:

• en overnattingsutgift = an accommodation expense
• overnattingsutgiften = the accommodation expense

The ending -en is doing the job that the does in English.

Yes, in Bokmål that can also be possible.

The head noun here is utgift, which is originally a feminine noun. In Bokmål, many feminine nouns can appear in either:

• a common-gender/masculine-style form: overnattingsutgiften
• or a feminine form: overnattingsutgifta

So both can be acceptable, depending on style, dialect, and personal preference.

Very roughly:

• overnattingsutgiften often feels more neutral in standard writing
• overnattingsutgifta may feel more clearly feminine and sometimes more spoken/dialect-friendly

Because høy agrees with a singular non-neuter noun.

Here the subject is singular, and the adjective comes after er, so it is a predicate adjective.

Compare:

• Utgiften er høy = singular, non-neuter
• Beløpet er høyt = singular, neuter
• Utgiftene er høye = plural

So in your sentence, høy is the correct form.

Because predicate adjectives in Norwegian do not usually show definiteness the way adjectives before a noun do.

After er, the adjective agrees mainly with:

• gender
• number

not with definiteness.

So:

• Overnattingsutgiften er høy is correct

But if the adjective comes before the noun, then definiteness matters:

• den høye overnattingsutgiften = the high accommodation expense

That difference is very important:

• after the verb: er høy
• before the noun: den høye ...

Because Norwegian usually uses høy for things like:

• prices
• costs
• expenses
• fees
• salaries

So:

• Prisen er høy = the price is high
• Utgiften er høy = the expense is high

Dyr means expensive, and it is more naturally used about the thing or service itself:

• Hotellet er dyrt = the hotel is expensive
• Det er dyrt å overnatte = it is expensive to stay overnight

So in this sentence, høy is the most natural choice.

You would normally say:

den høye overnattingsutgiften

This shows a common Norwegian pattern called double definiteness:

• den = definite article
• høye = adjective in definite form
• overnattingsutgiften = noun with definite ending

So:

• Overnattingsutgiften er høy = the accommodation expense is high
• den høye overnattingsutgiften = the high accommodation expense

English learners often find this surprising because English does not usually mark definiteness in two places like this.

This sentence has the normal word order for a simple Norwegian statement:

• Overnattingsutgiften = subject
• er = verb
• høy = complement

So it follows the basic pattern:

Subject + verb + complement

However, Norwegian is a V2 language, which means the finite verb is normally in the second position in main clauses. For example:

• Overnattingsutgiften er høy
• I år er overnattingsutgiften høy

In the second sentence, I år comes first, so er still stays in second position.

Yes, it is grammatical and natural, but it sounds a bit formal or administrative.

It fits well in contexts like:

• reports
• budgets
• travel reimbursement
• business writing

In more everyday speech, people might also say things like:

• Utgiftene til overnatting er høye
• Det er dyrt å overnatte

So your sentence is correct, but it has a somewhat official or written tone.