Skiladagurinn er á morgun.

Skiladagurinn means the due date or the deadline.

It comes from the noun skiladagur:

• skila = to hand in, submit, return
• dagur = day

So skiladagur is literally something like submission day or hand-in day.

Then Icelandic adds the definite article to the end:

• skiladagur = a due date / due date
• skiladagurinn = the due date

So in this sentence, skiladagurinn is the subject: the due date.

Because Icelandic usually puts the at the end of the noun instead of using a separate word like English does.

So:

• dagur = day
• dagurinn = the day

And similarly:

• skiladagur = due date
• skiladagurinn = the due date

This is called the suffixed definite article.
It is one of the first big differences English speakers notice in Icelandic.

The dictionary form is skiladagur.

That is the indefinite nominative singular form, which is the form dictionaries normally list.

Here are the two most useful forms to compare:

• skiladagur = a due date
• skiladagurinn = the due date

If you want to look the word up, search for skiladagur, not skiladagurinn.

The -inn is the definite article attached to the noun.

But there is also a small stem change involved, because the base noun is skiladagur, not skiladagu.

Compare:

• dagur = day
• dagurinn = the day

So:

• skiladagur = due date
• skiladagurinn = the due date

This pattern is normal for many masculine nouns ending in -ur.

It is nominative singular.

Why?

Because it is the subject of the sentence:

• Skiladagurinn = the due date
• er = is
• á morgun = tomorrow

So the structure is basically:

The due date + is + tomorrow

Subjects are typically in the nominative case in Icelandic, just as in many other languages with case systems.

Á morgun means tomorrow.

This is a very common fixed expression in Icelandic.

Even though á is normally a preposition meaning on and morgun is related to morning, the whole phrase á morgun should usually just be learned as the normal adverbial expression for tomorrow.

So in this sentence:

• Skiladagurinn er á morgun.
• The due date is tomorrow.

Historically, it is built from words that relate to that idea, but in modern Icelandic you should treat á morgun as a set phrase meaning tomorrow.

So for a learner, the safest approach is:

• memorize á morgun = tomorrow

Do not try to translate it word-for-word every time.

Because Icelandic normally uses the fixed expression á morgun for tomorrow.

English uses a single adverb, tomorrow, but Icelandic often expresses time with a prepositional phrase instead.

So this is simply the idiomatic Icelandic way to say it.

Historically and grammatically, morgun is a noun, but in the phrase á morgun the whole expression functions like an adverb of time.

So in practice, you can think of:

• á morgun = tomorrow

This is often the most useful way for learners to understand it.

Er means is.

It is the 3rd person singular present tense of the verb að vera = to be.

So:

• ég er = I am
• þú ert = you are
• hann / hún / það er = he / she / it is

In this sentence:

• Skiladagurinn er á morgun.
• The due date is tomorrow.

The sentence uses a very normal Icelandic word order:

• Skiladagurinn = subject
• er = verb
• á morgun = time expression

So it is basically:

Subject + verb + time phrase

This is straightforward and natural.

You could also say:

• Á morgun er skiladagurinn.

That would put more emphasis on tomorrow.
Both are grammatical, but the original sentence is the more neutral way to present the information.

Yes.

Depending on context, skiladagur can be translated as:

• due date
• deadline
• sometimes submission date

The best English choice depends on what is being handed in:

• homework
• an essay
• a form
• taxes
• an application

So The due date is tomorrow and The deadline is tomorrow can both be correct.

A rough pronunciation guide for English speakers is:

SKI-la-da-gu-rinn er ow MOR-gun

A few helpful notes:

• Stress in Icelandic usually falls on the first syllable:
  SKI-la-da-gu-rinn
• The sk before i sounds more like sky- than English sk-
• The g in dagurinn is softer than a hard English g
• á is pronounced like ow in cow
• morgun begins with a clear mor-

You do not need perfect pronunciation right away, but it helps to notice the first-syllable stress pattern.

It is masculine.

You can tell this from its form and from the way the definite article appears:

• skiladagur = due date
• skiladagurinn = the due date

The last part of the compound is dagur (day), which is masculine, and compounds usually take their gender from the final element.

Yes.

Icelandic, like English, often uses the present tense when talking about scheduled future events.

Compare in English:

• The due date is tomorrow.

That is present tense in form, but future in meaning.

The Icelandic sentence works the same way:

• Skiladagurinn er á morgun.

So there is nothing unusual about using er here.

Usually, no, not if you mean the due date in a specific situation.

• Skiladagurinn er á morgun. = The due date is tomorrow.

Using skiladagur without the definite article would sound less natural here unless you were speaking in a more general or unusual way.

In most normal contexts, if both speaker and listener know which due date is being discussed, Icelandic uses the definite form:

• skiladagurinn

Yes.

It has everything needed for a full sentence:

• Skiladagurinn = subject
• er = verb
• á morgun = complement/time expression

So it is a simple, complete, natural Icelandic sentence.