Days of the Week in Japanese: Seven Planets, Then the Dates

Here's the short version: the days of the week in Japanese all end in the same syllables. Every name closes with 曜日ようび (youbi), and the only thing that changes is one character at the front. Sun, moon, fire, water, wood, metal, earth — Sunday through Saturday, in that order. That's the whole list.

Those seven characters aren't a random set. They're seven lights: the sun, the moon, and the five planets you can find without a telescope. English names its week after the same seven, by a longer road. So this isn't seven new words. It's a list you already carry, respelled.

Dates are the harder half, and they're harder for one reason. A Japanese calendar is printed over an older page. Most of it is the modern grid — take the number, add a suffix, done. But in a few worn spots the older page shows through, and those spots are exactly the readings you can't guess. This note walks the week, the days of the month, the months, the clock, and the day words you'll need before Friday.

Start with the ending, because you only learn it once. 曜日ようび (youbi) means day of the week, and it's glued to the back of all seven names. What's left is a single character each, and they run in a fixed order.

Those front characters are the first kanji almost any course teaches, which is why the week arrives so early. 水みず (mizu) is water on its own and 水曜日すいようび (suiyoubi) on a Wednesday — one word, quietly teaching you both of its readings.

Say a friend asks which evening you're free. One day name, one particle, and you've answered:

金曜日は暇ですきんようびはひまです (kin'youbihahimadesu)

Friday is free.

Here's the whole week, with the character at the front of each name and the light that character points at.

The set has a name: 七曜しちよう (shichiyou), the seven luminaries. It's the sun, the moon, and the five planets bright enough to find with your eyes. It reached Japan through Chinese astrology in the Heian period, centuries before anybody used it to run a week.

Those element characters arrive by way of the planets, not straight from the elements themselves. Mars in Japanese is 火星かせい (kasei), the fire star. Mercury is the water star, Jupiter the wood star, Venus the metal star, Saturn the earth star. Line those five up and you have Tuesday through Saturday, in order, with the sun and the moon holding Sunday and Monday.

English got to the same seven lights by a different road. The two weeks share an ancestor and then traveled apart, one west into Latin and one east through China. The Romance languages still wear it plainly — mardi is Mars, mercredi Mercury, jeudi Jupiter, vendredi Venus. English kept Saturn, the sun and the moon, then handed the four days in the middle to Germanic gods — which is why Tuesday through Friday don't look the part.

Point at the reddish one on a clear night and you already have a sentence:

火星は赤い星ですかせいはあかいほしです (kaseihaakaihoshidesu)

Mars is the red planet.

That's the useful part. You aren't memorizing seven arbitrary syllables. You're relabeling a list you've carried since childhood.

From the 11th onward, a Japanese day of the month is the number plus 日にち (nichi). 十一日じゅういちにち (juuichinichi), 十二日じゅうににち (juuninichi), and on to the end of the month. That part is the modern grid, and you can build it yourself the first time you need it.

The first ten days are where the older page shows through. They use the native counting series — the ひとつ (hitotsu), ふたつ (futatsu), みっつ (mittsu) family from our numbers field note — so the readings look nothing like the digits printed beside them:

二日ふつか (futsuka), 三日みっか (mikka), 四日よっか (yokka), 五日いつか (itsuka), 六日むいか (muika), 七日なのか (nanoka), 八日ようか (youka), 九日ここのか (kokonoka), 十日とおか (tooka). Japanese children learn them as a chant, and so, in the end, does everyone else.

Which leaves the 1st — the strangest-looking of the lot, and the most reasonable. 一日ついたち (tsuitachi) is 月つき (tsuki), moon or month, plus 立ちたち (tachi), standing or starting, worn down over centuries into the word you say now. Under a lunar calendar the new moon starts the new month, so the reading isn't really an exception. It's a description nobody got around to replacing.

Read the same two characters as 一日いちにち (ichinichi) and the meaning slides to one whole day — a length, not a date. That single slip is the classic one:

❌ 五月いちにちに着きますごがついちにちにつきます (gogatsuichinichinitsukimasu) — arriving in May for one whole day

⭕ 五月一日に着きますごがつついたちにつきます (gogatsutsuitachinitsukimasu) — arriving on the first of May

Above ten, three days spoil the pattern, and that's the end of the list. The 14th and the 24th hand 四日よっか (yokka) back — 十四日じゅうよっか (juuyokka) and 二十四日にじゅうよっか (nijuuyokka) — and the 20th keeps an old reading of its own, 二十日はつか (hatsuka). Everything else in the second half of the month is a number with a suffix.

Months are the easiest thing on the Japanese calendar. Take the number, add 月がつ (gatsu), and you're finished. January is 一月いちがつ (ichigatsu), December is 十二月じゅうにがつ (juunigatsu), and there's no second set of names hiding behind them.

Three of the twelve keep an older reading. April is 四月しがつ (shigatsu), not yongatsu. July is 七月しちがつ (shichigatsu), not nanagatsu. September is 九月くがつ (kugatsu), not kyuugatsu.

Hold on to those three digits — four, seven, nine. They're about to come back.

Say you're telling someone when a course starts:

四月に学校が始まりますしがつにがっこうがはじまります (shigatsunigakkougahajimarimasu)

School starts in April.

Nine months out of twelve, you'll say the name correctly the first time you try it.

If you can say a number, you already know most of how to tell time in Japanese. Number plus 時じ (ji) gives you the hour, 半はん (han) on the end gives you half past, and 午前ごぜん (gozen) and 午後ごご (gogo) do the work of a.m. and p.m.

And there they are again. Four o'clock is 四時よじ (yoji), not yonji — the same clipped よ (yo) the counters use. Seven is 七時しちじ (shichiji). Nine is 九時くじ (kuji), not kyuuji.

These get learned as words rather than worked out as sums. That is what the older page does to a calendar: it decides, in a handful of places, that the number on the grid is not the thing you say.

Fixing a time is the sentence you'll build most often:

九時半に会いましょうくじはんにあいましょう (kujihanniaimashou)

Let's meet at half past nine.

The に (ni) pinning that to a point in time is a particle, and the N5 grammar list takes it apart properly. Here it just sits there and works.

Put the three troublemakers beside the digit 1 and the shape of the problem gets easy to see.

It's worth counting the damage, because it's smaller than it looks. Thirty-one days, twelve months, twelve hours on the clock face: fifty-five slots in total. The readings you can't work out from the digit come to nineteen, and two of those nineteen are the 14th and the 24th handing 四日よっか (yokka) straight back to you.

Nineteen readings, and you've met most of them already. Minutes have sound changes of their own — 分ふん (fun) turning into 分ぷん (pun) after certain numbers — but those belong with the counters, where the numbers field note keeps them.

The Japanese date format runs from the outside in: year, then month, then day, then the weekday in parentheses. Big to small, all the way down. Family names come first in Japanese too, and an address starts with the prefecture — the same direction, whatever the reason.

On a notice the weekday shrinks to a single character in parentheses. 金きん (kin) means Friday there and 土ど (do) means Saturday — the same characters you met at the front of 金曜日きんようび (kin'youbi) and 土曜日どようび (doyoubi), on a shorter shift. Opening hours and closing notices use that shorthand constantly, and the field note on Japanese signs reads a few of them.

Spoken aloud, a date keeps the same order:

三月九日に着きますさんがつここのかにつきます (sangatsukokonokanitsukimasu)

(I) arrive on the 9th of March.

Official forms often want the era year rather than the Western one, and 令和れいわ (reiwa) counts from 2019. That's the one place where the older page isn't showing through so much as still doing the paperwork.

Most of the time you won't say a date at all. You'll say today, or tomorrow, or last week, and Japanese keeps a tidy set for exactly that.

今日きょう (kyou), 明日あした (ashita), 昨日きのう (kinou), and one step further out in each direction, おととい (ototoi) and あさって (asatte). Weeks take a matching frame: 先週せんしゅう (senshuu), 今週こんしゅう (konshuu), 来週らいしゅう (raishuu). Months and years follow the same three-way shape, so the pattern pays for itself quickly.

今日きょう (kyou) hides a small gift. Read those two characters formally and you get 今日こんにち (konnichi) — the word sitting inside こんにちは (konnichiwa). The greeting has been carrying today around the whole time.

Three questions cover most of a week's small talk:

今日は何曜日ですかきょうはなんようびですか (kyouhanan'youbidesuka)

What day is it today?

今日は何日ですかきょうはなんにちですか (kyouhanannichidesuka)

What's the date today?

今何時ですかいまなんじですか (imananjidesuka)

What time is it?

Answer any of them with a bare word and you'll be understood. 金曜日ですきんようびです (kin'youbidesu) is a complete answer, and so is 九時半ですくじはんです (kujihandesu).

Sunday through Saturday, they are 日曜日にちようび (nichiyoubi), 月曜日げつようび (getsuyoubi), 火曜日かようび (kayoubi), 水曜日すいようび (suiyoubi), 木曜日もくようび (mokuyoubi), 金曜日きんようび (kin'youbi) and 土曜日どようび (doyoubi). Every name ends in 曜日ようび (youbi), and the character in front of it names the sun, the moon, or one of the five planets you can see without a telescope.

Because they're named after planets, and the Japanese names of those planets carry the elements. Mars is the fire star, Mercury the water star, Jupiter the wood star. The set is called 七曜しちよう (shichiyou), the seven luminaries, and it came to Japan through Chinese astrology in the Heian period. English reached the same seven lights by a different route, which is why Saturday and Saturn still match.

Outside in: year, then month, then day, then the weekday in parentheses, each number carrying its own character behind it. The weekday is abbreviated to one character there — 金きん (kin) for Friday. Official forms often ask for the era year rather than the Western year, and 令和れいわ (reiwa) counts from 2019.

今何時ですかいまなんじですか (imananjidesuka) — literally now, what hour is it. Open with すみません (sumimasen) if you're stopping a stranger. The answer comes back as the number plus 時じ (ji), often with 半はん (han) for half past, so 九時半ですくじはんです (kujihandesu) is half past nine.

Because it isn't a number. 一日ついたち (tsuitachi) comes from 月つき (tsuki), moon or month, plus 立ちたち (tachi), standing or starting — the day a new month begins. Read as 一日いちにち (ichinichi), the same two characters mean one whole day, which is a length rather than a date.

Everything above sits inside Ukiyoe Japanese as something to practice rather than something to reread. The concept lesson Numbers, Time & Counters holds the same three digits with reviewed readings and example sentences. The Dates & time readings drill turns them into questions — ついたち (tsuitachi), ようか (youka), よじ (yoji), くじ (kuji), one at a time, until the guessing stops.

And the characters at the front of the week are the first kanji set most people meet: 日ひ (hi), 月つき (tsuki), 火ひ (hi), 水みず (mizu), 木き (ki), 金きん (kin), 土つち (tsuchi). Seven characters, each with its origin story. Learn those and you've read the week — the same seven lights, in your own hand.