Kostgodtgjørelsen følger dagsatsen under forutsetning av at tjenestereisen er lang.

In Norwegian, the definite article is usually attached to the end of the noun:

• kostgodtgjørelse = a meal allowance / subsistence allowance

• kostgodtgjørelsen = the meal allowance

• dagsats = a daily rate

• dagsatsen = the daily rate

• tjenestereise = a business trip / official trip
• tjenestereisen = the business trip

In this kind of administrative sentence, the speaker is referring to specific, known things: the allowance, the daily rate, the business trip.

Because Norwegian normally writes compound nouns as one word.

So:

• kost
  • godtgjørelse → kostgodtgjørelse
• tjeneste
  • reise → tjenestereise

This is very common in Norwegian and often surprises English speakers, since English would usually write these as separate words, like meal allowance or business trip.

Grammatically, yes, følger is the present tense of følge, which often means to follow.

But in this sentence it is used in a more administrative sense:

• følger dagsatsen = is in accordance with the daily rate / uses the daily rate / is based on the daily rate

So this is not about physically following something. It means that the allowance is set according to that rate.

Dagsats literally means day rate or daily rate.

In official or workplace contexts, it often means a fixed amount paid per day according to a rule, tariff, or policy. So here dagsatsen is the standard daily amount that the allowance is calculated from.

It is a formal expression meaning:

• on the condition that
• provided that
• assuming that

You can think of it as a set phrase often used in legal, official, and administrative Norwegian.

Structure:

• under forutsetning av at
  • clause

So:

• under forutsetning av at tjenestereisen er lang
  = provided that the business trip is long

Yes, in simpler everyday Norwegian, you often could.

For example:

• Kostgodtgjørelsen følger dagsatsen hvis tjenestereisen er lang.

That is easier and more conversational.

But there is a difference in tone:

• hvis = neutral, everyday if
• under forutsetning av at = formal, official, policy-style wording

So the original sentence sounds like something from a handbook, contract, or travel-expense rules.

Because lang is a predicate adjective referring to tjenestereisen, which is singular.

Very roughly:

• singular common gender noun: lang
• singular neuter noun: langt
• plural: lange

Since tjenestereisen is a singular common-gender noun, the correct form is:

• tjenestereisen er lang

If the noun were neuter, you would use langt. If it were plural, you would use lange.

Here it means long in duration, not physically long.

Since tjenestereise means a trip made for work, lang in this context refers to how long the trip lasts. In administrative language, this usually matters because payment rules often depend on the duration of the trip.

The sentence breaks down like this:

• Kostgodtgjørelsen = subject
• følger = verb
• dagsatsen = object/complement after the verb
• under forutsetning av at tjenestereisen er lang = adverbial phrase expressing a condition

So the core structure is:

• [Subject] + [Verb] + [Object] + [Condition]

This is a normal main-clause word order in Norwegian.

Because at introduces the clause that states the condition.

Compare:

• under forutsetning av noe = under the assumption/condition of something
• under forutsetning av at ... = under the condition that ...

So in this sentence:

• av at tjenestereisen er lang

introduces the full clause tjenestereisen er lang.

This is part of the fixed expression, so it is best learned as a whole:

• under forutsetning av at

It is natural, but it sounds formal and bureaucratic.

A native speaker would expect this kind of wording in:

• company travel policies
• reimbursement rules
• government documents
• HR manuals

In everyday speech, a person would probably say something simpler, such as:

• Du får kostgodtgjørelse etter dagsatsen hvis tjenestereisen er lang.

So the original sentence is good Norwegian, but clearly belongs to an official register.