kosta ("to cost") is the verb you reach for every time you shop, ask a price, or weigh up a decision. It is mechanically simple — a fully regular weak Class-1 verb — but it behaves differently from English in one important way: you will almost always meet it in the third person, because the thing that "costs" is the subject (Hvað kostar þetta? "How much does this cost?"). The price itself goes in the accusative. Get those two habits right and kosta gives you no trouble at all.
Conjugation
Class: weak, Class 1 (the -a- conjugation: past in -aði). Auxiliary: hafa — það hefur kostað "it has cost." The full personal paradigm is given for completeness, but in real use kosta lives mostly in the 3rd person (kostar, kostaði).
| Principal parts | |
|---|---|
| Infinitive | að kosta |
| 3sg present | kostar |
| 3sg past | kostaði |
| Supine | kostað |
| Person | Present (nútíð) | Past (þátíð) |
|---|---|---|
| ég | kosta | kostaði |
| þú | kostar | kostaðir |
| hann / hún / það | kostar | kostaði |
| við | kostum | kostuðum |
| þið | kostið | kostuðuð |
| þeir / þær / þau | kosta | kostuðu |
| Person | Present subjunctive | Past subjunctive |
|---|---|---|
| ég | kosti | kostaði |
| þú | kostir | kostaðir |
| hann / hún / það | kosti | kostaði |
| við | kostum | kostuðum |
| þið | kostið | kostuðuð |
| þeir / þær / þau | kosti | kostuðu |
| Non-finite & imperative | |
|---|---|
| Imperative (þú) | kostaðu (rare; only in the "cost (someone)" sense) |
| Supine | kostað |
| Past participle (m/f/n) | kostaður / kostuð / kostað |
| Middle voice (miðmynd) | kostast — not in ordinary use |
The default shape: Hvað kostar þetta?
Unlike English, where a person can be the subject of cost only metaphorically, in Icelandic the thing is the subject and kosta sits in the third person. The everyday question is Hvað kostar þetta? ("How much does this cost?"), and the answer keeps the same frame: Það kostar… ("It costs…").
Hvað kostar þetta?
How much does this cost?
Afsakið, hvað kosta tómatarnir?
Excuse me, how much do the tomatoes cost?
Miðinn kostaði ekki neitt — hann var ókeypis.
The ticket didn't cost anything — it was free.
The price is in the accusative
The amount something costs is a direct object in the accusative: Það kostar fimm hundruð krónur ("It costs five hundred krónur"). The price phrase is what answers Hvað?, and kosta governs the accusative on it. With plain numbers and krónur the accusative is invisible, but with a noun like mikið ("a lot") or with the definite forms it shows.
Það kostar þúsund krónur að komast inn.
It costs a thousand krónur to get in.
Nýi síminn kostaði mig hálf mánaðarlaun.
The new phone cost me half a month's wages.
Hvað kostar að senda þetta til Íslands?
How much does it cost to send this to Iceland?
kosta einhvern eitthvað — cost someone something
kosta can take two objects, both accusative: the person it costs and the thing it costs them — það kostaði mig mikið ("it cost me a lot"). This works for money but also figuratively, for effort, time, or sacrifice — exactly like English "it cost him his job".
Mistökin kostuðu hann starfið.
The mistake cost him his job.
Það kostar þig ekkert að spyrja.
It costs you nothing to ask.
Common Mistakes
❌ Hvað kostar þetta krónur?
Incorrect — for 'how much', Hvað kostar þetta? is complete; don't add 'krónur'
✅ Hvað kostar þetta?
How much does this cost?
❌ Ég kosta tíu þúsund krónur.
Incorrect — the thing costs, not the person; the buyer isn't the subject
✅ Það kostar tíu þúsund krónur.
It costs ten thousand krónur.
❌ Bókin kostuð tvö þúsund krónur í gær.
Incorrect — the 3sg past is the regular kostaði, not 'kostuð'
✅ Bókin kostaði tvö þúsund krónur í gær.
The book cost two thousand krónur yesterday.
❌ Það kostaði mér mikið.
Incorrect — the person costed is accusative (mig), not dative (mér)
✅ Það kostaði mig mikið.
It cost me a lot.
Key Takeaways
- kosta / kostar / kostaði / kostað — fully regular weak Class 1 (-aði past).
- It lives in the 3rd person: the thing costs — Hvað kostar þetta? / Það kostar…
- The price is accusative: það kostar þúsund krónur.
- kosta
- two accusatives = "cost someone something": það kostaði mig mikið (the person is mig, not mér).
- Orthography: kosta has an o-stem, so it shows no u-umlaut (kostum, kostuðu keep the o); only a-stems umlaut to ö.
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- Shopping and Service PhrasesA2 — The survival phrases for shops, restaurants, and services — Hvað kostar þetta?, Ég ætla að fá ..., Get ég borgað með korti? — built around the key verb-choice habit that Icelandic orders with 'fá' (get), not 'kaupa' (buy) or 'vilja' (want), plus the case each phrase governs.
- The Weak Preterite: -aði, -di, -ði, -tiA2 — How to choose and form the weak past tense — Class-1 -a verbs take -aði (tala → talaði, plural töluðum), Class-2 verbs take the short dental -di/-ði/-ti picked by the preceding sound (reyndi, dæmdi, keypti) — with the full tala paradigm and the 'when in doubt, -aði' default for unknown verbs.