Álagningin kemur á morgun.

It is the definite article attached to the noun.

• álagning = assessment / levy / tax notice (depending on context)
• álagningin = the assessment / the levy / the tax notice

In Icelandic, the is very often added to the end of the noun instead of being a separate word.

Koma is the infinitive, meaning to come.

In the sentence, the verb has to match the subject Álagningin because it is third person singular, so the correct form is kemur:

• ég kem = I come
• þú kemur = you come
• hann/hún/það kemur = he/she/it comes

So Álagningin kemur means The assessment comes / is coming / will come.

Because Icelandic often uses the present tense for future meaning, especially when something is scheduled, expected, or clearly placed in the future by a time expression.

So:

• Álagningin kemur á morgun = The assessment comes tomorrow / will come tomorrow

This is very similar to English sentences like:

• The train leaves tomorrow
• My package arrives tomorrow

A more explicit future is possible, but the present tense is the most natural here.

á morgun means tomorrow.

This is a very common fixed expression and should really be learned as a whole phrase.

It is different from:

• í morgun = this morning

So:

• Álagningin kemur á morgun = The assessment comes tomorrow
• Álagningin kom í morgun = The assessment came this morning

This is a very common learner confusion, so it is worth memorizing early.

It is in the nominative case because it is the subject of the sentence.

The thing that is doing the action of coming is Álagningin, so nominative is what you would expect here.

A useful way to think about it is:

• What comes tomorrow?
  Álagningin

That makes it the subject.

Yes, álagning is feminine.

That matters because the form of the attached definite article depends on gender, number, and case. In this sentence, Álagningin is feminine singular nominative definite.

You do not need to memorize the full grammar label every time, but it helps explain why the noun looks the way it does.

Yes. That is also correct and natural.

Icelandic word order is fairly flexible, but there is an important rule: the finite verb usually stays in second position in main clauses.

So both of these work:

• Álagningin kemur á morgun
• Á morgun kemur álagningin

But Á morgun álagningin kemur is not the normal word order.

It can absolutely be used for things like mail, notices, bills, results, and other non-human things.

So in this sentence, kemur means something like:

• arrives
• comes out
• is delivered
• is issued

depending on the context.

That makes koma a very useful everyday verb, much broader than just a person physically coming somewhere.

The main stress in Icelandic is usually on the first syllable of each word.

So the rhythm is roughly:

• Álagningin
• KEmur
• á MORgun

A rough English-style approximation would be:

• OW-lag-ning-in KEH-mur ow MOR-gun

The approximation is not perfect, but the most important thing for a learner is: stress the first syllable.