Áminningin kemur á réttum tíma, því dagatalið mitt er fullt í þessari viku.

Because Icelandic usually adds the definite article to the end of the noun.

• áminning = reminder
• áminningin = the reminder

So Áminningin means the reminder. Here it is the subject of the sentence. The base noun áminning is feminine, singular, and áminningin is the definite nominative singular form.

Kemur is the 3rd person singular present tense of koma, which means to come.

So:

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

In this sentence, Áminningin kemur means the reminder comes or more naturally the reminder arrives.

This phrase is in the dative.

The expression á réttum tíma means at the right time or on time. In this kind of time expression, á takes the dative, so the adjective must match:

• réttur tími = right time (nominative)
• á réttum tíma = at the right time (dative)

A useful detail: tíma looks the same in both accusative and dative singular, but the adjective réttum clearly shows that the phrase is dative.

This is a good example of how Icelandic adjectives change form to agree with the noun in gender, number, and case.

Here því means because.

So this part:

því dagatalið mitt er fullt í þessari viku

means:

because my calendar is full this week

Yes, you could also say af því að, which is very common in everyday Icelandic:

• Áminningin kemur á réttum tíma, því dagatalið mitt er fullt í þessari viku.
• Áminningin kemur á réttum tíma, af því að dagatalið mitt er fullt í þessari viku.

Both are correct. Því on its own can sound a bit more written or formal than af því að.

In Icelandic, the most neutral way to say my calendar is often:

definite noun + possessive

So:

• dagatalið mitt = my calendar

This is very common in Icelandic. The noun gets the suffixed definite article, and the possessive comes after it.

Mitt dagatal is also possible, but it usually sounds more emphatic or contrastive, something like:

• my calendar
• my own calendar
• my calendar, not someone else’s

So in an ordinary statement, dagatalið mitt is the most natural choice.

Because dagatal is a neuter noun, and predicate adjectives in Icelandic agree with the subject.

The adjective fullur changes like this in the singular:

• fullur = masculine
• full = feminine
• fullt = neuter

Since dagatalið is neuter singular, you get:

dagatalið mitt er fullt = my calendar is full

If the subject were feminine, you would use full. If it were masculine, you would use fullur.

Because í takes the dative when it means in in a static sense, including a time frame like in this week / this week.

• þessi vika = this week (nominative)
• í þessari viku = in this week / this week (dative)

The noun vika is feminine, so the forms are:

• nominative: þessi vika
• accusative: þessa viku
• dative: þessari viku

A very useful contrast is:

• í þessari viku = in this week, during this week
• færa fundinn í þessa viku = move the meeting into this week

So í þessa viku can happen, but usually when there is a sense of movement or change into that time period.

Yes. Just like in English, Icelandic can use fullur/full/fullt about a schedule, calendar, or planner.

So dagatalið mitt er fullt means that there is no free time left in it. It does not mean the calendar is physically stuffed with something.

This is a very natural use of fullt.

Related ideas you might also hear:

• Dagbókin mín er full. = My planner is full.
• Ég er bókaður / bókuð. = I’m booked.

Because the sentence has two clauses:

1. Áminningin kemur á réttum tíma
2. dagatalið mitt er fullt í þessari viku

The second clause gives the reason for the first one, and því connects them as because. In standard Icelandic writing, a comma is commonly used before this kind of reason clause.

So the comma helps show the structure:

statement, because reason

Yes, a couple of small ones.

First, the basic clause order here is straightforward:

• Áminningin = subject
• kemur = verb
• á réttum tíma = adverbial phrase

Then after því, you get another clause:

• dagatalið mitt = subject
• er = verb
• fullt = complement
• í þessari viku = time phrase

Nothing is unusual here, but the sentence shows two very common Icelandic patterns that feel different from English:

• the definite article attached to the noun: áminningin, dagatalið
• the possessive after the noun: dagatalið mitt

So even though the overall word order is fairly simple, the noun phrases are built in a characteristically Icelandic way.