After the gymnastics of declining 1-4, the rest of the numbers feel like a holiday: from fimm (five) upward they are, for practical purposes, invariant — one fixed form that counts masculines, feminines and neuters alike. This page gives you the inventory (five through the tens, hundreds and thousands) and the rules for building bigger numbers with og "and." But there is one twist that genuinely surprises learners, and we'll meet it head-on: a big number that ends in 1, 2, 3 or 4 makes that final element re-inflect for gender. So 121 books is not "fixed" at all — it's hundrað tuttugu og *ein bók*.
The basic inventory: 5 to 20
Here are the cardinals you simply memorise. None of them changes for gender or, in ordinary use, for case.
| 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|
| fimm | sex | sjö | átta | níu | tíu |
| 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|
| ellefu | tólf | þrettán | fjórtán | fimmtán |
| 16 | 17 | 18 | 19 | 20 |
|---|---|---|---|---|
| sextán | sautján | átján | nítján | tuttugu |
fimm hestar, sex bækur, sjö börn
five horses, six books, seven children — fimm/sex/sjö never change for gender.
Ég er sautján ára.
I'm seventeen (years old). (sautján — invariant)
Það eru tólf mánuðir í árinu.
There are twelve months in the year. (tólf)
The tens
The multiples of ten are likewise fixed forms:
| 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
|---|---|---|---|---|---|---|---|
| tuttugu | þrjátíu | fjörutíu | fimmtíu | sextíu | sjötíu | áttatíu | níutíu |
Amma mín er níutíu ára.
My grandmother is ninety. (níutíu)
Það búa um fimmtíu manns í þorpinu.
About fifty people live in the village. (fimmtíu)
Watch the spelling of fjörutíu (40) — the ö, not a — and sjötíu (70) with ö. These two trip people up.
Building compounds with og — and the 1-4 twist
To say a number like 21, 34 or 99, Icelandic joins the ten and the unit with og "and": tuttugu *og einn, þrjátíu og fjórir, níutíu **og níu. English drops the "and" (*twenty-one); Icelandic keeps it.
Here is the surprise. We said 5-and-up is invariant — but a compound that ends in one of the inflecting numerals 1, 2, 3 or 4 makes that final element decline for gender, exactly as it would on its own. The big number is fixed; its tail is not.
þrjátíu og tvær bækur
thirty-two books — bók is feminine, so the '2' is the feminine tvær, not tveir.
tuttugu og ein króna
twenty-one krónur — króna is feminine, so '1' is ein (and króna stays singular!).
fjörutíu og þrír menn
forty-three men — masculine, so '3' is þrír.
Two things to absorb from those examples. First, gender agreement reaches across the whole compound to its last word: it's tvær in þrjátíu og tvær bækur because bækur is feminine. Second — easy to miss — when a number ends in "… og einn," the counted noun is grammatically singular: tuttugu og ein króna (one króna, twenty-one times over), literally "twenty and one króna." English forces the plural ("twenty-one krónur"); Icelandic follows the final "one."
hundrað and þúsund — they are nouns
"Hundred" and "thousand" are not just bigger numbers; they are neuter nouns (hundrað, þúsund — both hk). Because they're nouns, they pluralise, and the count of them is itself a number that agrees: since they're neuter, "two hundred" uses the neuter tvö.
| Number | Icelandic | Note |
|---|---|---|
| 100 | (eitt) hundrað | neuter noun |
| 200 | tvö hundruð | neuter tvö + plural hundruð |
| 300 | þrjú hundruð | neuter þrjú |
| 1000 | (eitt) þúsund | neuter noun |
| 3000 | þrjú þúsund | neuter þrjú |
| 1,000,000 | ein milljón | milljón is feminine → ein, not eitt |
Það komu tvö hundruð gestir á tónleikana.
Two hundred guests came to the concert. (neuter tvö; plural hundruð)
Miðinn kostaði þrjú þúsund krónur.
The ticket cost three thousand krónur. (þrjú þúsund)
Ísland fær um eina milljón ferðamanna á ári.
Iceland gets about a million tourists a year. (um + accusative → eina; milljón is feminine, so ein, not eitt)
Note the genders clash usefully here: hundrað and þúsund are neuter, so they pair with tvö/þrjú, but milljón is feminine, so it pairs with ein (ein milljón, not eitt milljón). That is a real exam-and-everyday distinction.
Reading a long number aloud
Putting it all together, a number like 121 books stacks hundreds, tens and the unit, joining the last two with og, and lets the final element agree:
hundrað tuttugu og ein bók
a hundred and twenty-one books — note: the final '1' is feminine ein (bók is feminine) AND the noun is singular bók.
tvö þúsund tuttugu og sex
two thousand and twenty-six (e.g. a year) — ends in 'sex', so nothing re-inflects.
So the rule "5 and up is invariant" is true of the number's body but not its tail. Scan to the end: if it lands on einn, tveir, þrír or fjórir, agree it with the noun; otherwise relax.
Common Mistakes
❌ þrjátíu og tveir bækur
Incorrect — bækur is feminine, so the final '2' must be tvær: þrjátíu og tvær bækur.
✅ þrjátíu og tvær bækur
thirty-two books
❌ tuttugu og einn króna
Incorrect — króna is feminine, so '1' is ein (and the noun is singular): tuttugu og ein króna.
✅ tuttugu og ein króna
twenty-one krónur
❌ tvö hundrað gestir
Incorrect — hundrað is a noun and pluralises after 'two': tvö hundruð gestir.
✅ tvö hundruð gestir
two hundred guests
❌ eitt milljón
Incorrect — milljón is feminine, so 'one' is ein: ein milljón.
✅ ein milljón
one million
❌ tuttugu einn (with no 'og')
Incorrect — Icelandic joins the ten and unit with og: tuttugu og einn.
✅ tuttugu og einn
twenty-one
Key Takeaways
- From fimm up, cardinals are essentially invariant — one form regardless of the noun's gender.
- Compounds join the ten and unit with og: tuttugu og einn, þrjátíu og fjórir.
- The twist: if the number ends in 1-4, that final element re-inflects for gender (þrjátíu og tvær bækur), and a final "… og einn" makes the noun singular (tuttugu og ein króna).
- hundrað and þúsund are neuter nouns that pluralise — tvö hundruð, þrjú þúsund — while milljón is feminine (ein milljón).
- Spelling traps: fjörutíu (40), sjötíu (70) with ö; the teens all end in -tán.
Now practice Icelandic
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Icelandic→Related Topics
- Declining 1-4: einn, tveir, þrír, fjórirA2 — The full gender-and-case paradigms of the four Icelandic numerals that inflect — einn/ein/eitt, tveir/tvær/tvö, þrír/þrjár/þrjú, fjórir/fjórar/fjögur — including the oblique cases (acc, dat tveimur/þremur/fjórum, gen tveggja/þriggja/fjögurra) that drive prepositions and compounds like þriggja herbergja íbúð.
- Telling Time and DatesA2 — How to tell the clock and say the date in Icelandic — klukkan er þrjú, the half-hour trap (hálf níu = 8:30, counting UP to the next hour like German), korter yfir/í for quarters, the 24-hour clock, and dates built on ordinals (fjórði júní, þann fimmta).