I booked a dentist appointment in Osaka for what I thought was the 4th of the month. I showed up on the 4th. The appointment was on the 8th. よっか (*yokka*, the 4th) and ようか (*youka*, the 8th) are one vowel apart, and I'd mixed them up reading a text message. The receptionist was kind about it. I still check these twice now.
That mix-up is basically the whole challenge of Japanese dates in one story. The months are easy, almost suspiciously easy. The days of the week are a short, clean list. But the days of the month use a set of irregular readings for the first ten days that don't follow any pattern you can guess your way into. You just have to learn them. Here's the full system, in the order I'd learn it if I were starting over.
Months: just a number plus 月
This is the part that makes Japanese feel generous after the kanji-heavy stuff you've likely already struggled through. There are no separate words for January, February, March. Every month is just its number followed by 月 (*gatsu*, "moon" or "month").
- 一月 (*ichigatsu*): January
- 二月 (*nigatsu*): February
- 三月 (*sangatsu*): March
- 四月 (*shigatsu*): April
- 五月 (*gogatsu*): May
- 六月 (*rokugatsu*): June
- 七月 (*shichigatsu*): July
- 八月 (*hachigatsu*): August
- 九月 (*kugatsu*): September
- 十月 (*juugatsu*): October
- 十一月 (*juuichigatsu*): November
- 十二月 (*juunigatsu*): December
Two irregularities to flag before you assume it's all clean number-reading. April is shigatsu, using the *shi* reading of 四 instead of the more common *yon*. September is kugatsu, using *ku* instead of *kyuu* for 九. Both exist because *yon* and *kyuu* just don't sound as natural here, the same way English doesn't always pick the most "logical" pronunciation either. Outside of those two, the months are exactly what they look like: number plus 月.
In casual writing and on calendars, you'll often just see the numeral: 1月, 4月, 9月. The kanji 月 stays, the number swaps to digits. Both forms are completely normal, and you'll see the digit version more in daily life (train schedules, receipts, apps).
Days of the week: a short, memorizable set
The seven days each end in 曜日 (*youbi*, literally "day of the shining/luminary"), preceded by a character tied to one of the classical elements or celestial bodies. If you've studied any Chinese-derived calendar system before, this pattern might look familiar.
- 月曜日 (*getsuyoubi*): Monday (moon)
- 火曜日 (*kayoubi*): Tuesday (fire)
- 水曜日 (*suiyoubi*): Wednesday (water)
- 木曜日 (*mokuyoubi*): Thursday (wood)
- 金曜日 (*kinyoubi*): Friday (gold/metal)
- 土曜日 (*doyoubi*): Saturday (earth)
- 日曜日 (*nichiyoubi*): Sunday (sun)
Notice that 月 (moon) shows up again here for Monday, same character as "month," different reading (*getsu* instead of *gatsu*). That's normal for kanji. Most characters have multiple readings depending on context, and 月 is one of the more visible examples of it.
In speech, the 日 at the end is frequently dropped in casual conversation. Someone asking what day a meeting is on might just say 火曜 (*kayou*) instead of the full 火曜日. Both are correct. The full form is safer in writing or anything formal.
A memory trick that actually works
The five middle days (火水木金土, Tuesday through Saturday) come straight from the traditional five elements: fire, water, wood, gold, earth. If you've ever encountered these elements in other contexts (Chinese astrology, feng shui, certain fantasy games), the order will already feel half-familiar. Moon and sun bookend the week for Monday and Sunday, which also lines up with how the week is named in a lot of other languages if you trace the etymology back far enough.
Days of the month: the part with no shortcuts
Here's where things stop being predictable. Counting days of the month uses a special set of readings for the 1st through the 10th, plus a few more irregular ones scattered through the rest of the month. Days 11 and beyond mostly follow a regular number-plus-日 pattern, with a couple of exceptions.
The first ten days (irregular, just memorize these)
- 一日 (*tsuitachi*): the 1st
- 二日 (*futsuka*): the 2nd
- 三日 (*mikka*): the 3rd
- 四日 (*yokka*): the 4th
- 五日 (*itsuka*): the 5th
- 六日 (*muika*): the 6th
- 七日 (*nanoka*): the 7th
- 八日 (*youka*): the 8th
- 九日 (*kokonoka*): the 9th
- 十日 (*touka*): the 10th
一日 (*tsuitachi*) for the 1st doesn't resemble the number 一 (*ichi*) at all. It's an old word tied to the start of the lunar month, and it just has to be memorized as its own item, not derived from anything. The rest, from the 2nd through the 10th, follow an older native Japanese counting system (*futatsu*, *mittsu*, *yottsu*...) rather than the *ichi, ni, san* system you'd use to count most things. That's why they don't look like the numbers you already know.
This is also where my dentist appointment went wrong. 四日 (*yokka*, 4th) and 八日 (*youka*, 8th) differ by one vowel sound and one mora, and under text-message speed-reading conditions, they're easy to swap. If you take one thing from this article, let it be: slow down on よっか vs ようか specifically.
11th through 19th, and 20th
From the 11th onward, the pattern mostly normalizes to [number]日, read with the regular *-nichi* counter.
- 十一日 (*juuichinichi*): the 11th
- 十二日 (*juuninichi*): the 12th
- 十四日 (*juuyokka*): the 14th (irregular, echoes 四日)
- 二十日 (*hatsuka*): the 20th (irregular, its own word)
- 二十四日 (*nijuuyokka*): the 24th (irregular, echoes 四日 again)
The 14th, 20th, and 24th are the outliers in the second half of the month. 二十日 (*hatsuka*) especially doesn't follow anything you could predict, it's just a fixed word for the 20th the same way 一日 is fixed for the 1st. The 14th and 24th borrow the irregular *yokka* reading from the 4th rather than using the expected *juuyonnichi* or *nijuuyonnichi*. Every other day from 11 to 31 uses the plain number-plus-*nichi* pattern: 十三日 (*juusannichi*, 13th), 十五日 (*juugonichi*, 15th), 二十一日 (*nijuuichinichi*, 21st), and so on.
Why this matters more than it seems
Dates come up constantly in daily life in Japan: making appointments, reading receipts, checking when a package arrives, understanding a friend's birthday. Unlike a lot of vocabulary you can defer until you need it, date readings show up immediately and often, which makes the irregular first-ten-days list worth front-loading rather than picking up gradually.
Putting a full date together
A full date in Japanese goes year, then month, then day, the reverse order from English. For example, "July 24th, 2026" becomes:
2026年7月24日 (*nisen nijuuroku-nen shichigatsu nijuuyokka*)
- 年 (*nen*): year counter, attached to the year number
- 月 (*gatsu*): month counter, attached to the month number
- 日 (*nichi*, but irregular for the specific days above): day counter
If you want to add a weekday, it goes at the end, often in parentheses on forms and calendars: 2026年7月24日（金曜日） for a Friday. Practically speaking, once you know the year-month-day order and have the irregular day-of-month readings down, constructing any date is mostly assembly, not new memorization.
A quick reference for asking about dates
A few phrases that come up constantly once you start using this system in conversation:
- 今日は何曜日ですか (*kyou wa nan youbi desu ka*): What day of the week is it today?
- 今日は何日ですか (*kyou wa nan nichi desu ka*): What's the date today?
- 誕生日はいつですか (*tanjoubi wa itsu desu ka*): When is your birthday?
Notice 誕生日 (*tanjoubi*, birthday) ends in the same 日 you've been reading all article, just tucked into a longer compound word. Once the day-of-month readings feel solid, you'll start noticing 日 doing this kind of work everywhere.
Where to go from here
The kanji here (月, 火, 水, 木, 金, 土, 日, 年) are common enough that they're worth being able to read on sight, even before you tackle a full kanji study plan. If you're still building up your kana foundation before jumping into kanji-heavy vocabulary like this, the getting started with hiragana guide is the right starting point.
For more everyday vocabulary that comes up as often as dates do, the 5 essential Japanese phrases article covers the greetings and set expressions you'll use daily. And if you want to drill the kana that make up these readings until they're automatic, Hirakata's study mode is built for exactly that kind of repetition.