Days of the Week and Months in Japanese

The pattern behind the calendar words

Most Japanese calendar words follow a simple, repeating shape, and only one corner of the system is genuinely hard. The days of the week all end in the same suffix, 曜日 (youbi), so once you know the seven leading characters you know all seven days. The months are even easier: take a number and add 月 (gatsu), and you have the month. That is eleven of the twelve months done almost for free, with three small exceptions you can memorize in a minute.

The one part worth slowing down for is the days of the month. The 1st through the 10th use old native-Japanese counting readings that you have to learn as their own small set, and a few later days (the 14th, 20th, and 24th) keep readings from that same family. Everything past the 10th is mostly just a number plus にち (nichi), which is regular and predictable.

So here is where to spend your effort. Skim the days of the week and the months, since they reward you quickly. Save your real attention for the first ten days of the month. If you know that going in, the whole calendar stops feeling like a wall of memorization and starts feeling like three patterns plus one short list.

The seven days of the week

Every day of the week in Japanese ends in 曜日 (youbi), and the character in front of it names a celestial body or classical element. The lovely part is that this is the same logic as the week in English and the Romance languages: the seven days are named after the sun, the moon, and the five planets visible to the naked eye, which in the East Asian tradition carry the names of the five classical elements. So 火 (fire) is the day of Mars, 水 (water) is the day of Mercury, 木 (wood) is the day of Jupiter, 金 (metal or gold) is the day of Venus, and 土 (earth) is the day of Saturn.

Once you see the parallel, the list is easier to hold. Sunday and Monday come from the sun (日) and the moon (月), exactly as in English. The remaining five are the planets in their element names. You are not memorizing seven unrelated words; you are memorizing one suffix and seven familiar bodies in the sky.

The twelve months

A month in Japanese is just its number plus 月 (gatsu), so January is 1月 (ichigatsu), February is 2月 (nigatsu), and the pattern holds straight through to December. Three months break the rule, and the exception is always the number reading rather than the 月 part: 4月 is read しがつ (shigatsu), not yongatsu; 7月 is しちがつ (shichigatsu), not nanagatsu; and 9月 is くがつ (kugatsu), not kyuugatsu.

These three irregular readings are not random. They mirror the same readings of 4, 7, and 9 that show up elsewhere in Japanese numbers, where shi, shichi, and ku appear in fixed expressions and counters. If you have met those readings before, the months will feel like an old pattern rather than a new exception, and learning one set reinforces the other.

Days of the month, the genuinely irregular part

This is the part to slow down for: the 1st through the 10th of the month use special native-Japanese counting readings that you cannot derive from the number. They are leftovers from an older counting system, and they have to be learned as a set rather than reasoned out. The good news is that it is a short, finite list, and once it is in your memory the rest of the calendar follows easily.

From the 11th onward the system becomes friendly again. Most days are simply the number plus にち (nichi), so the 11th is じゅういちにち (juuichinichi) and the 15th is じゅうごにち (juugonichi), formed exactly the way you would guess. The pattern holds for the bulk of the month, which is why the first ten days are the only stretch that needs deliberate memorization.

Three later days are the exceptions to watch. The 14th, written 14日, keeps the よっか (yokka) sound from the 4th and is read じゅうよっか (juuyokka), and the 24th does the same as にじゅうよっか (nijuuyokka). The famous outlier is the 20th, 20日, which is read はつか (hatsuka) with its own special reading rather than the number plus にち. If you learn the 4th as よっか (yokka) and remember that the 14th and 24th inherit it, plus はつか (hatsuka) for the 20th, you have covered every irregular day past the first ten.

Putting a full date together

Japanese dates run from large to small: the year first, then the month, then the day of the month, and finally the day of the week. This is the reverse of the common English habit of leading with the day, and it lines up with how Japanese handles many ordered things, moving from the widest unit down to the most specific. Once you expect that order, reading and saying a date becomes a matter of slotting the words you already know into a fixed sequence.

Here is a worked example using only the words from the tables above. Suppose you want to say the third of April, and that it falls on a Tuesday. You take the month, 4月 (shigatsu), then the day of the month, 3日 (mikka), then the day of the week, 火曜日 (kayoubi). Spoken in order, that is shigatsu mikka kayoubi: April, the 3rd, Tuesday. Notice that each piece comes straight from a pattern you have already met, the irregular month reading shigatsu, the native day reading mikka, and the weekday kayoubi, so building the date is just assembly, not new memorization.

The same method works for any date. Pick the month, attach the right day-of-month reading (a special one if it is in the first ten days or one of the later exceptions, otherwise the number plus にち), and finish with the weekday if you need it. Because the order never changes, the hard part is never the structure; it is only ever recalling the individual day-of-month word, which is exactly the set worth drilling.

How to learn these without rote misery

Spend almost no time grinding the days of the week and the months, and spend your real effort on the 1st through the 10th. The weekday list collapses into one suffix plus seven familiar celestial bodies, and the months are a number plus 月 (gatsu) with only three irregular readings. Both of those reward a quick read-through and a few passes far more than they reward heavy drilling, so do not over-invest in the easy parts.

Treat the first ten days of the month as a single block to memorize together. They form a rhythm when you say them in sequence, tsuitachi, futsuka, mikka, yokka, itsuka, muika, nanoka, youka, kokonoka, tooka, and learning them as one chant is far easier than meeting them one at a time across separate study sessions. Once that block is solid, add the three later exceptions, the 14th, the 20th as はつか (hatsuka), and the 24th, and you are essentially finished.

Spaced repetition is the tool that makes a small irregular set stick without misery. Rather than rereading the list and hoping, review each day-of-month reading at the moment you are about to forget it, so the hard ones surface more often and the easy ones fade into the background. If you want that handled for you, Inku is a calm iPhone flashcard app that schedules reviews with FSRS spaced repetition and ships with bundled audio, so you can hear each reading while you learn it instead of guessing at the sounds. The aim is steady, quiet exposure: a few minutes a day on the genuinely irregular readings, and the rest of the calendar will already be carrying itself.

Common questions

Related reading

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• Japanese numbers
• N5 time vocabulary
• JLPT N5 vocabulary list
• Learn hiragana

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