Learn Hardcore Icelandic: Í lok vikunnar mun hún hafa klárað öll verkefnin sín. - At the end of the week she will have finished all her projects.

So: „mun hún hafa klárað“ = “she will have finished”, i.e. the action is completed before a certain point in the future (here: the end of the week).

If you said „mun hún klára öll verkefnin sín“, that’s more like “she will finish all her tasks” (sometime in the future, not necessarily by a specific deadline).

English has the same contrast:

She will finish her tasks. (simple future)
She will have finished her tasks (by the end of the week). (future perfect)

Icelandic mirrors that contrast with mun + hafa + past participle for the future perfect.

Why does the sentence start with „Í lok vikunnar“ and then have „mun“ right after it?

Icelandic main clauses are basically verb-second (like German): the finite verb tends to be in the second slot in the sentence.

The structure here is:

Í lok vikunnar – adverbial phrase (“at/by the end of the week”)
mun – finite verb (future auxiliary)
hún – subject
hafa klárað öll verkefnin sín – rest of the verb phrase + object

If you started with the subject instead, you’d say:

Hún mun hafa klárað öll verkefnin sín í lok vikunnar.

Same meaning. Moving „Í lok vikunnar“ to the front just emphasizes the time frame more strongly and still obeys the verb‑second pattern: [time] – [finite verb] – [subject] – …

What does „Í lok vikunnar“ literally mean, and why is „vikunnar“ in that form?

Literally:

í = in / at
lok = end (a neuter noun)
vikunnar = of the week (genitive singular of vika, “week”)

So „í lok vikunnar“ is literally “in the end of the week”, which corresponds to English “at the end of the week” or “by the end of the week”.

Grammar points:

Í with a time phrase like this usually triggers the dative on the noun that follows, but lok is a neuter noun whose dative singular form looks the same as nominative/accusative (lok).
vikunnar is genitive singular of vika:
- nominative: vika (a week)
- genitive: vikunnar (of the week)

Structure:

í [lok [vikunnar]] = in the end of the week.

Could you say something like „í endanum á vikunni“ instead of „í lok vikunnar“?

Not in natural, idiomatic Icelandic for this meaning.

„í endanum á vikunni“ is grammatically understandable, but it sounds clumsy and unidiomatic here.
The standard, natural way to say “at/by the end of the week” is „í lok vikunnar“.

Think of „í lok“ + genitive as a fixed, very common pattern for time expressions:

í lok dagsins – at the end of the day
í lok mánaðarins – at the end of the month
í lok ársins – at the end of the year

How would you say “by the end of this week” or “by the end of next week”?

You keep the same structure „í lok“ and change the word for “week”:

by/at the end of this week
- Í lok þessarar viku (more explicit)
- Often people still just say í lok vikunnar if it’s clear from context that “this week” is meant.
by/at the end of next week
- Í lok næstu viku

So the pattern is: í lok + [genitive/possessive phrase for “week”].

Why is it „öll verkefnin sín“ and not „sín öll verkefnin“ or something else?

The order quantifier – noun (with definite ending) – possessive is normal in Icelandic:

öll – “all” (quantifier)
verkefnin – “the tasks” (definite plural of verkefni)
sín – reflexive possessive “her (own)”

So „öll verkefnin sín“ = “all her (own) tasks”.

Typical orders:

öll verkefnin mín – all my tasks
allar bækurnar hans – all his books

If you put sín first (sín öll verkefnin), it sounds wrong/unnatural. Quantifiers like allur, enginn, margir generally come before the noun, while possessives (like mín, þín, sín, hans, hennar) usually come after a definite noun phrase.

What is the difference between „sín“ and „hennar“ in this sentence?

Both can translate as “her”, but they are used differently:

sín is a reflexive possessive: it refers back to the subject of the same clause.
hennar is a non‑reflexive possessive: it refers to some other female, not the subject.

In this sentence:

hún … öll verkefnin sín
- sín refers back to hún → her own tasks.

If you said:

Í lok vikunnar mun hún hafa klárað öll verkefnin hennar.

that would normally mean:

By the end of the week she will have finished all *her tasks — where *“her” = some other woman, not the subject.

So:

sín = her own (subject’s own)
hennar = her (some other woman’s)

Why is it „öll“ and not some other form, and how does it relate to „verkefnin“?

Öll is the neuter plural form of allur (“all”).

verkefni (“task, assignment”) is neuter.
verkefnin is neuter plural definite: the tasks.

Adjectives and quantifiers agree in gender, number, and case with the noun:

neuter plural (accusative here) → öll verkefnin

Other forms of allur for comparison:

masculine singular nominative: allur (all)
feminine singular nominative: öll
neuter singular: allt
neuter plural: öll

So:

allt verkefnið – the whole task / all (of) the task (singular)
öll verkefnin – all the tasks (plural)

What exactly is „klárað“, and how is the verb phrase „hafa klárað“ formed?

Klárað is the past participle of the verb klára (“to finish, complete”).

The perfect (and future perfect) is formed with:

hafa (“to have” as auxiliary) + past participle

So:

Present perfect: Hún hefur klárað öll verkefnin sín.
- She has finished all her tasks.
Future perfect: Hún mun hafa klárað öll verkefnin sín.
- She will have finished all her tasks.

Here the past participle is:

infinitive: að klára
past participle (neuter form used with hafa): klárað

This is very similar to English have finished / will have finished.

Could you express the idea with „vera búin að“ instead of „hafa klárað“?

Yes, that’s also very common and sounds natural, with a slight nuance:

Í lok vikunnar
verður hún búin að klára öll verkefnin sín.

This literally means:

verður – will be
búin að klára – done with finishing / have finished

So it’s like: “By the end of the week she will be done (with) finishing all her tasks.”

Nuance:

hafa klárað focuses a bit more on the completed action itself (will have finished).
vera búin að klára emphasizes the resulting state (she will be in the state of having them done).

In practice both are very natural for this kind of sentence.

Why is „mun hún“ the order here? Could you also say „hún mun hafa klárað…“?

Yes, you can say both, depending on what you put at the beginning:

With a time phrase first (as in your sentence):
- Í lok vikunnar mun hún hafa klárað öll verkefnin sín.
  Structure: [time] – mun – [subject] – …
With the subject first:
- Hún mun hafa klárað öll verkefnin sín í lok vikunnar.
  Structure: [subject] – mun – …

The verb‑second rule means the finite verb (mun) goes right after whatever comes first in the clause. So:

Start with Í lok vikunnar → next must be mun, then hún.
Start with Hún → next is mun, then the rest.

Both orders are correct; they just differ in what you emphasize first (the time frame vs. the subject).