Once you can count in Danish, the next step is putting numbers to work in time: how long something lasts, how soon it will happen, and how often it recurs. The hard part for English speakers is not the numbers — it is the prepositions. English uses one word, "in," for two completely different meanings ("I'll be done in two hours" = a future point; "I finished it in two hours" = the time it took). Danish splits these apart with three different prepositions — i, om and på — and choosing wrong genuinely changes what you said. This page builds your duration and frequency vocabulary on top of that split.
The three-way split: i / om / på
This is the centrepiece. With a span of time plus a number, Danish forces you to choose:
| Preposition | Meaning | Example | English |
|---|---|---|---|
| i | duration — for how long | i to timer | for two hours |
| om | future point — how soon from now | om to timer | in two hours (from now) |
| på | completion — within / it took | på to timer | in / within two hours |
i — duration
I + a time span answers "for how long?" The action fills the whole stretch.
Vi ventede i to timer, før bussen kom.
We waited for two hours before the bus came.
Han har boet i Aarhus i ti år.
He has lived in Aarhus for ten years.
In casual speech the i is often dropped — Vi ventede to timer is perfectly natural — but it is never wrong to keep it, and you should be able to recognise both.
om — a future point
Om + a time span answers "how soon from now?" It locates a moment in the future, measured from the present.
Jeg er færdig om ti minutter.
I'll be done in ten minutes (from now).
Toget kører om et kvarter.
The train leaves in a quarter of an hour.
This is the meaning English speakers reach for first, and that instinct is exactly why they misuse i. "I'll be done in two hours" is om to timer, not i to timer. (I to timer would mean you will be in the state of being-done for two hours, which is nonsense.)
på — completion within a span
På + a time span answers "in how much time was it completed?" — the time it took to finish a bounded task, or a deadline you must finish within.
Hun løb maratonet på under fire timer.
She ran the marathon in under four hours.
Kan du nå at læse rapporten på en time?
Can you manage to read the report within an hour?
The mental test: på answers "how long did it take?", i answers "how long did it last?", om answers "how long until?".
The deeper logic and the rest of the time-preposition system are covered in prepositions/paa-tid; here the focus is putting numbers into these frames.
Duration without a preposition: time taken as the subject
You can also state a duration with tage ("to take"):
Det tager tyve minutter at gå derhen.
It takes twenty minutes to walk there.
Hele processen tog os næsten en uge.
The whole process took us almost a week.
And to mark a deadline as a point on the clock, use inden or senest:
Rapporten skal være færdig inden fredag.
The report has to be finished by Friday.
Frequency: how often
Frequency is built with gang ("time, occurrence") plus om + the definite time period. The pattern is [number] gang(e) om [definite period].
| Danish | English |
|---|---|
| en gang om dagen | once a day |
| to gange om ugen | twice a week |
| tre gange om måneden | three times a month |
| en gang om året | once a year |
Note two details. First, the period takes the definite ending: dagen, ugen, måneden, året — literally "once about the day." Second, the singular is en gang and the plural is to gange (with the -e).
Tag medicinen to gange om dagen, morgen og aften.
Take the medicine twice a day, morning and evening.
Vi ses kun en gang om året, til jul.
We only see each other once a year, at Christmas.
For "every other / every Nth," Danish reuses the distributive hver with an ordinal (see determiners/hver-enhver):
Hun har nattevagt hver anden dag.
She works night shifts every other day.
Spans with fra … til — "from … to"
To mark the boundaries of a stretch, use fra X til Y:
Jeg arbejder fra ni til fem på hverdage.
I work from nine to five on weekdays.
Butikken har åbent fra mandag til lørdag.
The shop is open from Monday to Saturday.
Putting it together
Mødet varer i en time, så jeg er hjemme om halvanden time.
The meeting lasts for an hour, so I'll be home in an hour and a half.
Watch that sentence carefully: i en time is the duration of the meeting, and om halvanden time is the future point when you arrive home — two different prepositions because two different meanings, even within one breath. (And note halvanden = "one and a half," a single Danish word.)
How this differs from English
English overloads the word "in." "I'll be there in an hour" (future point) and "I built it in an hour" (time taken) use the identical preposition, and "for an hour" handles duration. Danish refuses this overloading: future point = om, time taken = på, duration = i. There is no shortcut and no way to feel your way to the right one from English — you have to attach each Danish preposition to its meaning directly. The frequency pattern is also un-English: where English says "twice a week" with the indefinite "a," Danish says to gange om ugen with om + the definite noun. Treat om X-en as a fixed frame for "per X."
Common Mistakes
❌ Jeg er færdig i ti minutter.
Incorrect — a future point needs om, not i. As written it means 'I'll be finished for ten minutes.'
✅ Jeg er færdig om ti minutter.
I'll be done in ten minutes (from now).
❌ Vi ventede om to timer ved stationen.
Incorrect — duration needs i (or no preposition), not om.
✅ Vi ventede i to timer ved stationen.
We waited for two hours at the station.
❌ Hun skrev opgaven i tre timer og afleverede den.
Incorrect if you mean it took three hours to finish — completion needs på.
✅ Hun skrev opgaven på tre timer og afleverede den.
She wrote the assignment in three hours and handed it in.
❌ Jeg løber to gange om en uge.
Incorrect — the period takes the definite ending and no 'en': om ugen.
✅ Jeg løber to gange om ugen.
I run twice a week.
❌ Tag pillen to gang om dagen.
Incorrect — plural of gang is gange.
✅ Tag pillen to gange om dagen.
Take the pill twice a day.
Key Takeaways
- i = duration ("for two hours," i to timer) — often droppable in speech.
- om = a future point ("in two hours from now," om to timer).
- på = completion / time taken ("done within two hours," på to timer).
- Frequency = [number] gang(e) om [definite period]: en gang om dagen, to gange om ugen.
- hver anden dag = "every other day"; fra ni til fem = "from nine to five."
- English collapses om and på into one "in" — keep them apart in Danish.
Now practice Danish
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Start learning Danish→Related Topics
- Prepositions of TimeA2 — How Danish splits English 'in' across i, om, and på for time — including the crucial i to timer / om to timer / på to timer three-way distinction.
- Time ExpressionsA2 — Everyday Danish time words — i dag, i går, i morgen, i forgårs, i overmorgen — and the crucial for...siden vs om split for past and future.
- Dates, Time and MoneyA2 — Telling the time in Danish (including the half-hour trap where halv ti means 9:30), reading dates with ordinals, saying years, and handling kroner and øre.