In English, you state the number of years that you are, and attach the phrase “years old” or “year old” to the number to state your age.  In Japanese, it works much like the same way, expect that there are some pronunciation changes that some of the numbers go through.  The suffix sai (さい) means “years old”.  See if you can see any irregularities in the numbers:

1 year old: いっさい

2 years old: にさい

3 years old: さんさい

4 years old: よんさい

5 years old: ごさい

6 years old: ろくさい

7 years old: ななさい

8 years old: はっさい

9 years old: きゅうさい

10 years old: じゅっさい

Ok, so the irregular ones are 1 and 8.  1 just by itself is いち, but when you add the suffix さい to it, it changes to いっさい.  The same goes for 8.  8 by itself is はち, but when you add さい you get はっさい.  Both 1 and 8 end in ち.  When ち is pronounced just before さ, the pronounciation will change to either はっ or いっ.  These changes are meant so that it’ll be easier to pronounce.  One more thing I want to note is that 1 years old and 8 years old is pronounced as issai (いっさい) not itsusai (いつさい), and hassai (はっさい) not hatsusai (はつさい).  The small tsu (っ) indicates a double consonant.

Another thing to note is that 4 years old is よんさい.  よさい and しさい is incorrect.  Also for 7 years old, しちさい will not work.  If you look at the explantion above, you’ll see why.  For 9 years old, its きゅうさい not くさい. 

To form numbers 11-19, just take the second digit ending and add it to じゅう.  11 years old will be じゅういっさい.  1 is the second digit in 11 and since 1 years old is いっさい, attach that to じゅう and you get 11 years old.

One another thing to note is that you might hear people use はたち for 20 years old a lot more often than にじゅっさい.  Technically にじゅっさい is not wrong, so feel free to use it.  Just be aware though, that はたち also means the same thing.  Just like 20 years old, 30 years old, 40, 50 and so on are formed in the same way.  Take the number for 30 and add sai (さい).  No biggie.

See you next time!

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