Japanese Numbers & Dates: The Irregular Readings That Trip Everyone Up

Japanese has two sets of number readings: native Japanese (ひとつ, ふたつ…) and Sino-Japanese (いち, に, さん…). Dates and counters mix them, and the leftovers from the older native system survive in the most common words, especially the days of the month.

This is why 1日 is ついたち (a completely different word) and 20日 is はつか. You cannot derive these; you memorize them. The reward is that they are extremely high-frequency, so the effort pays back immediately.

Months are far more regular than days: 一月 (いちがつ), 二月 (にがつ), 三月 (さんがつ), and so on through 十二月 (じゅうにがつ), simply the number plus がつ. The one exception worth flagging is 四月 (April), read しがつ rather than よんがつ. Every other month follows the plain number reading you already know.

Because this pattern is so regular, months rarely cause the same trouble that days of the month do. Learn the one exception and the rest falls out of numbers you already have.

One commonly cited explanation for why 4 and 9 carry alternate readings in certain contexts is that し (4) and く (9) sound like 死 (death) and 苦 (suffering), so speakers reach for よん and きゅう instead in situations where that association feels unwelcome, hospital room numbers and gift quantities are the examples most often mentioned. Treat this as a cultural note rather than a strict rule: both readings of 4 and 9 remain correct and widely used in ordinary counting.

For exam purposes, the reading that matters is whichever one is actually attached to the specific word you are learning (4日 is always よっか, 4時 is always よじ), rather than a general preference for one reading of the digit over the other.

Prices use the same Sino-Japanese numbers as counting in general, with 円 (えん) attached at the end: 300円 is さんびゃくえん. The main thing to watch is the sound changes in the hundreds and thousands place (百 can become びゃく or ぴゃく, 千 can become ぜん), the same kind of shift covered in the counter sound-changes article.

Phone numbers work completely differently from every other number in this article: each digit is read individually rather than combined into a single large number, and the hyphen is read の. 090-1234-5678 becomes ゼロ・キュウ・ゼロ・の・イチ・ニ・サン・ヨン・の・ゴー・ロク・ナナ・ハチ, often in katakana-style clipped pronunciation, with 0 read as ゼロ and long vowels added to some digits (ご becomes ゴー) for clarity over the phone.

The counter for people is 〜人 (にん), but the first two are irregular: 一人 ひとり (one person), 二人 ふたり (two people). From three onward it is regular: 三人 さんにん, 四人 よにん, 五人 ごにん.