Prepositions of Time | Icelandic Grammar

Time expressions are where Icelandic prepositions feel least logical and most like vocabulary. A great many of them are frozen idioms — fixed units whose case you cannot reliably predict from the rule and simply have to learn whole: í dag ("today"), í gær ("yesterday"), á morgun ("tomorrow"), í fyrra ("last year"). The good news is that once you've learned the frozen phrases, the productive patterns underneath them are tidy: a small set of prepositions (í, á, um, fyrir, eftir, frá ... til) carries almost all of time, and the two genuinely tricky distinctions — duration vs. point and "ago" vs. "in [a time]" — come down to choosing the right preposition and case. (Clock-time formation itself — klukkan þrjú and so on — belongs to numbers/dates-and-time; here we cover the prepositional frames.)

The frozen phrases: learn these as whole units

Some of the most frequent time words are idioms you should never try to parse. Learn them as fixed chunks, accent and all.

Phrase	Meaning	Note
í dag	today	frozen — don't analyse the case
í gær	yesterday	frozen
á morgun	tomorrow	frozen (singular)
í kvöld	tonight / this evening	frozen
í fyrra	last year	frozen
á morgnana	in the mornings (habitual)	contrast with á morgun

Hvað ætlar þú að gera í dag?

What are you going to do today? (í dag — frozen 'today')

Við hittumst í gær á kaffihúsinu.

We met yesterday at the café. (í gær — frozen 'yesterday')

Ég hringi í þig á morgun.

I'll call you tomorrow. (á morgun — frozen 'tomorrow', singular)

Watch the á morgun / á morgnana pair especially. Á morgun (singular) is "tomorrow"; á morgnana (plural with the article) is "in the mornings" as a habit. Same noun, different time meaning — a perfect illustration of why these are best learned as units, not assembled from rules.

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Treat í dag, í gær, á morgun, í kvöld, í fyrra as single vocabulary items, like English "today." Don't try to justify the case — just memorise the whole phrase, including the accent on í gær (never i gær).

í — for periods, and the "for a week" duration

Beyond the frozen phrases, í is the everyday preposition for enclosing periods — í janúar ("in January"), í sumar ("this summer / this coming summer"). Its most useful productive job is marking duration — "for [a length of time]" — and here it takes the accusative.

Ég verð í Reykjavík í viku.

I'll be in Reykjavík for a week. (í + accusative viku — duration 'for a week')

Hann var veikur í þrjá daga.

He was sick for three days. (í + accusative þrjá daga — duration)

Við bjuggum í Danmörku í mörg ár.

We lived in Denmark for many years. (í + accusative mörg ár — duration)

So "for a week" is í viku, "for three days" is í þrjá daga — duration with í + accusative. Hold on to that, because it contrasts directly with the next pattern.

eftir — "after" and "in [a time from now]" — accusative

eftir in time means "after", and it takes the accusative: eftir matinn ("after the meal"), eftir vinnu ("after work"). Crucially, eftir + a length of time means "in / after [that much time], counting forward from now" — eftir viku is "in a week / a week from now," a future point.

Við getum talað saman eftir matinn.

We can talk after the meal. (eftir + accusative matinn — 'after', and the case is visible here)

Ég kem aftur eftir tvo daga.

I'll be back in two days. (eftir + accusative tvo daga — a future point, 'two days from now')

Hringdu í mig eftir hádegi.

Call me in the afternoon / after noon. (eftir + accusative hádegi)

Be precise about the case: temporal eftir takes the accusative, not the dative. You will see eftir matinn (acc., visible because matur has distinct cases), eftir tvo daga (acc.), eftir vikuna (acc.). The dative eftir belongs to the spatial "along" sense (eftir veginum "along the road"), which is a different preposition-meaning, not the time one.

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Temporal eftir is accusative: eftir matinn, eftir tvo daga, eftir vikuna. Don't be tempted into the dative by a "rest = dative" instinct — that instinct is for the two-case prepositions, and eftir here is plain accusative.

The pair to master: í viku ("for a week") vs eftir viku ("in a week")

Here is the contrast English speakers get wrong most often, because English "in a week" is genuinely ambiguous and Icelandic forces you to disambiguate:

í viku = "for a week" — a duration you spend doing something (í
- accusative).
eftir viku = "in a week / a week from now" — a future point when something will happen (eftir
- accusative).

Ég ætla að vera í sumarbústaðnum í viku.

I'm going to stay at the summer house for a week. (í viku — duration)

Ég fer í sumarbústaðinn eftir viku.

I'm going to the summer house in a week (a week from now). (eftir viku — future point)

Same noun viku, both accusative, completely different meanings selected by the preposition. Í viku answers "how long?"; eftir viku answers "when?". Map English carefully: "I'll be there for a week" → í viku; "I'll be there in a week" → eftir viku.

á — days of the week, and "on [a day]" (accusative with the article)

To say something happens on a particular day, Icelandic uses á + the day name with the definite article, and the result is accusative: á mánudaginn ("on Monday"), á föstudaginn ("on Friday"). The article-plus-accusative is the giveaway that this is a specific upcoming (or just-past) day, not a habitual one.

Við förum í bíó á föstudaginn.

We're going to the cinema on Friday. (á + accusative-with-article föstudaginn — a specific day)

Fundurinn er á mánudaginn klukkan tíu.

The meeting is on Monday at ten. (á mánudaginn — specific day; klukkan tíu for the clock time)

For habitual "on Mondays / every Monday," Icelandic switches to the bare dative plural: á mánudaginn ("on Monday," one specific day) gives way to á mánudögum ("on Mondays," recurring). The contrast mirrors á morgun vs á morgnana: a single specific day on one side, the recurring habit on the other.

Ég fer í sund á morgnana.

I go swimming in the mornings. (habitual — plural á morgnana)

um — for stretches and recurring spans (accusative)

um + accusative covers spans like the weekend, the holidays, a season viewed as a stretch you move "around / through": um helgina ("over the weekend"), um jólin ("at Christmas / over Christmas").

Hvað gerðir þú um helgina?

What did you do over the weekend? (um + accusative helgina)

Við förum alltaf norður um jólin.

We always go north at Christmas. (um + accusative jólin)

fyrir — "ago" (dative) and "before"

To say "X ago," Icelandic puts fyrir first and the time in the dative: fyrir viku ("a week ago"), fyrir tveimur dögum ("two days ago"). This is the one place a time noun goes dative, and it surprises everyone because every other duration pattern is accusative.

Hún flutti til Íslands fyrir tveimur árum.

She moved to Iceland two years ago. (fyrir + dative tveimur árum — 'ago')

Ég talaði við hann fyrir tveimur dögum.

I spoke to him two days ago. (fyrir + dative tveimur dögum)

Notice the symmetry now: looking forward a week from now is eftir viku (accusative); looking back a week is fyrir viku (dative). Future → eftir + acc.; past → fyrir + dat. (For the full range of fyrir senses, see prepositions/fyrir-and-frame.)

frá ... til — spans from one point to another

For a stretch "from X to Y" — opening hours, a date range, a journey in time — Icelandic uses frá ... til. Both frá and til take their usual cases (frá + dative, til + genitive), so the noun after til goes genitive.

Búðin er opin frá níu til sex.

The shop is open from nine to six. (frá ... til span; both clock points)

Ég er í fríi frá mánudegi til föstudags.

I'm on holiday from Monday to Friday. (frá + dative mánudegi ... til + genitive föstudags)

Common Mistakes

❌ Ég kem aftur í tvo daga (meaning 'in two days from now').

Wrong preposition — 'in two days from now' is eftir tvo daga; í tvo daga means 'for two days' (duration).

✅ Ég kem aftur eftir tvo daga.

I'll be back in two days. (eftir = a future point)

The classic í / eftir mix-up. Í + acc. is duration ("for two days"); eftir + acc. is a future point ("in two days' time"). English "in" is ambiguous; Icelandic is not.

❌ Við hittumst eftir matnum.

Wrong case — temporal eftir is accusative: eftir matinn, not the dative matnum.

✅ Við hittumst eftir matinn.

We'll meet after the meal. (temporal eftir → accusative matinn)

Temporal eftir takes the accusative. The dative (eftir veginum) is reserved for the spatial "along" sense, which has nothing to do with time.

❌ Ég flutti hingað fyrir viku síðan, fyrir vikuna.

Wrong form — 'a week ago' is fyrir + dative viku, not the accusative/definite vikuna.

✅ Ég flutti hingað fyrir viku.

I moved here a week ago. (fyrir + dative viku — 'ago')

"X ago" is fyrir + dative: fyrir viku, fyrir tveimur dögum. This is the one time-pattern that breaks the accusative habit.

❌ Við förum í bíó á föstudag.

Incomplete — 'on Friday' (a specific day) needs the article: á föstudaginn, not the bare föstudag.

✅ Við förum í bíó á föstudaginn.

We're going to the cinema on Friday. (á + accusative-with-article)

"On [a specific day]" is á + the day with the definite article in the accusative: á föstudaginn, á mánudaginn. The bare noun is wrong here.

❌ Ég fer í sund á morgun (meaning 'in the mornings, habitually').

Wrong number — 'in the mornings' (habitual) is á morgnana; á morgun means 'tomorrow' (one specific day).

✅ Ég fer í sund á morgnana.

I go swimming in the mornings. (habitual → plural á morgnana)

á morgun (singular) = "tomorrow"; á morgnana (plural) = "in the mornings." A one-letter difference in your head, a big difference in meaning.

Key Takeaways

Many core time phrases are frozen idioms — í dag, í gær, á morgun, í kvöld, í fyrra — learned whole, accents included. Don't parse them.
Duration ("for a week") = í + accusative: í viku, í þrjá daga. A future point ("in a week / after the meal") = eftir + accusative: eftir viku, eftir matinn.
Temporal eftir is accusative, not dative — the dative eftir is the separate spatial "along."
"X ago" is the odd one out: fyrir + dative (fyrir viku, fyrir tveimur dögum). Forward = eftir
- acc.; back = fyrir
  - dat.
"On [a specific day]" = á + day + definite article (accusative): á föstudaginn. Habitual recurrence goes plural: á morgnana, á mánudögum.
Spans use frá ... til (frá
- dat., til
  - gen.): frá mánudegi til föstudags.

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