Ordinal Numbers 11th to 19th
When stating that an event happens on a specific calendar date, Icelandic uses the accusative case. Ordinal numbers behave like weak adjectives, modifying the understood masculine word dagur (day). For masculine weak adjectives, the nominative -i ending changes to -a in the accusative.
You will frequently see the word þann (the/that) placed immediately before the date, but it is sometimes left out.
| Number | Nominative | Accusative (Dates) |
|---|
| 11th | ellefti | ellefta |
| 12th | tólfti | tólfta |
| 13th | þrettándi | þrettánda |
| 14th | fjórtándi | fjórtánda |
| 15th | fimmtándi | fimmtánda |
(Note: The numbers 13th through 19th all follow the same pattern, ending in *-ándi and changing to -ánda).*
The 20s and 30s
The ordinals for the 20s and 30s use the base words tuttugasti (20th) and þrítugasti (30th).
When forming compound numbers like 21st or 31st, both parts of the number become ordinals, joined by og (and). For example, 21st is tuttugasti og fyrsti.
For calendar dates, both parts take the accusative -a ending. Therefore, tuttugasti og fyrsti becomes tuttugasta og fyrsta.
Listing Consecutive Dates
If an event like a hearing or investigation spans multiple days, simply list the numbers in their accusative -a form, connecting the final day with og.