20 to 99
Learn how to form Irish numbers from twenty to ninety-nine, covering both the modern decimal system and the traditional vigesimal (base-20) system.
Irish has two distinct systems for forming numbers from 20 to 99. The modern decimal (base-10) system is now the official standard taught in schools, while the traditional vigesimal (base-20) system remains common in Gaeltacht areas, especially for telling age and time. It is important to be able to recognise both.
The Decimal System
The decimal system is the most common way of counting in modern Irish. It follows a simple base-10 pattern, similar to English. The tens are unique words, and the units are added on.
Abstract Counting
For counting without a noun (e.g., in mathematics or reading out a phone number), the pattern is [Ten] a [Unit].
- 20:
fiche - 30:
tríocha - 40:
daichead - 50:
caoga - 60:
seasca - 70:
seachtó - 80:
ochtó - 90:
nócha
To form a number like 21, you combine the ten and the unit with a.
- fiche a haon - 21
- tríocha a dó - 32
- daichead a trí - 43
- caoga a ceathair - 54
Counting Nouns
When counting nouns, the structure depends on whether you are using a round ten (20, 30, 40) or a compound number (21, 32, 43).
For the tens (20, 30, 40, etc.)
The structure is [Ten] + [Noun]. The noun stays in the singular and is not mutated.
- fiche bád - 20 boats
- tríocha bliain - 30 years
- daichead euro - 40 euro
For compound numbers (21, 32, 43, etc.)
The structure is [Unit] + [Noun] + is + [Ten]. The unit number (1-9) comes first and determines the form of the noun and any mutation, just as with the numbers 1-10.
- bád is fiche - 21 boats (literally “boat and twenty”)
- dhá bhád is tríocha - 32 boats (“two boats and thirty”)
- seacht mbád is daichead - 47 boats (“seven boats and forty”)
The rules for the noun following the unit are:
| Unit | Noun Form & Mutation | Example (bád, boat) | Example (bliain, year) |
|---|---|---|---|
| 1 | Singular, no mutation | bád is fiche | bliain is fiche |
| 2 | Singular, lenition | dhá bhád is fiche | dhá bhliain is fiche |
| 3–6 | Plural, lenition | trí bhád is fiche | trí bliana is fiche |
| 7–9 | Plural, eclipsis | seacht mbád is fiche | seacht mbliana is fiche |
Ordinal Numbers
Ordinal numbers (“20th”, “21st”, “22nd”) also have different forms for tens and compound numbers.
For the tens (20th, 30th, 40th, etc.)
The tens add the suffix -ú or -dú.
-
20th:
an fichiú -
30th:
an tríochadú -
40th:
an daicheadú -
50th:
an caogadú -
60th:
an seascadú -
70th:
an seachtódú -
80th:
an t-ochtódú -
90th:
an nóchadú -
an fichiú bád - the 20th boat
-
an tríochadú bliain - the 30th year
For compound numbers (21st, 32nd, 43rd, etc.)
The structure is an + [Ordinal Unit] + [Noun] + is + [Ten].
- an t-aonú bád is fiche - the 21st boat
- an dóú bád is tríocha - the 32nd boat
- an tríú bád is daichead - the 43rd boat
The Vigesimal System
The vigesimal system is a traditional method of counting based on units of twenty (fiche). While less common in official use, it is still widespread in the Gaeltacht and in certain contexts like telling your age.
Why learn the vigesimal system?
The vigesimal system reflects an older way of counting that was once common across Celtic languages. Its name comes from the Latin for “twentieth”. You will encounter it frequently in conversations with native speakers, in traditional stories, and in set phrases. For example, a person who is 45 might say they are cúig is dhá fhichead (“five and two-score”) years old. Recognising these forms is key to understanding natural, spoken Irish.
Abstract Counting
The system builds numbers by adding to multiples of twenty.
- 20:
fiche - 30:
fiche a deich(20 and 10) - 40:
dhá fhichead(two twenties) - 50:
dhá fhichead a deich(two twenties and 10) - 60:
trí fichid(three twenties) - 70:
trí fichid a deich(three twenties and 10) - 80:
ceithre fichid(four twenties) - 90:
ceithre fichid a deich(four twenties and 10)
Numbers in between are formed by adding the unit.
- fiche a haon - 21 (20 and 1)
- dhá fhichead a cúig - 45 (two twenties and 5)
- trí fichid a dó dhéag - 72 (three twenties and 12)
Counting Nouns
Counting nouns with the vigesimal system is more complex and has several distinct patterns.
Numbers 21-39
This range has its own unique structures.
- 21:
bád is fiche(boat and twenty) - 22-30: The structure is
[Unit 2-10] + [Noun] + fichead.- dhá bhád fichead - 22 boats
- deich mbád fichead - 30 boats
- 31-39: The structure is
[Unit 11-19] + [Noun] + ar fhichid(“on twenty”).- aon bhád déag ar fhichid - 31 boats
- naoi mbád déag ar fhichid - 39 boats
Numbers 40 and above
From 40 onwards, the patterns become more regular.
- For multiples of 20 (40, 60, 80): The structure is
[Multiplier] + fichead/fichid + [Noun].- dhá fhichead bád - 40 boats
- trí fichid bád - 60 boats
- For compound numbers (41, 52, 63, etc.): The structure is
[Unit] + [Noun] + is + [Vigesimal Ten].- bád is dá fhichead - 41 boats
- dhá bhád déag is dá fhichead - 52 boats (12 boats and two twenties)
- seacht mbád déag is trí fichid - 77 boats (17 boats and three twenties)
Ordinal Numbers
Ordinal numbers in the vigesimal system follow the structure of the cardinal numbers.
- 20th:
an fichiú bád - 22nd:
an dóú bád fichead - 31st:
an t-aonú bád déag ar fhichid - 40th:
an dá fhicheadú bád - 41st:
an t-aonú bád is dá fhichead - 60th:
an trí ficheadú bád - 72nd:
an dóú bád déag is trí fichid