The Japanese Calendar: Days, Weeks, Months, and Years

The Calendar Is Non-Negotiable

You can avoid keigo for a while. You can survive without counters for flat objects. But the calendar? It comes up constantly — making plans, booking reservations, talking about birthdays, understanding due dates. If you want to function in Japanese, this is required vocabulary.

The good news: most of the calendar system is logical. The bad news: the days of the month have some of the most irregular readings in the entire language. But we'll get through it.

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Part 1: Days of the Week (曜日)

The seven days of the week use 曜日 (yōbi) as a suffix, with each day named after a classical element — the same system that gave us the planets in many languages.

Memory Tricks

The elements follow a pattern you might already know:

• 月曜日 — Moonday (Monday)
• 日曜日 — Sunday (Sunday)
• 土曜日 — Saturday (Saturn = earth/soil in this system)

For the rest, try associations:

• 火曜日 (fire) — Tuesday is 火🔥 (think: "taco Tuesday is fire")
• 水曜日 (water) — Wednesday starts with Water
• 木曜日 (wood) — 木 looks like a tree, Thursday = Tree day
• 金曜日 (gold) — Friday is payday = gold 💰

Shortening

In casual writing, calendars, and schedules, the 曜日 is often shortened to just the element kanji:

月　火　水　木　金　土　日

You'll see this on train timetables, school schedules, and calendar apps everywhere.

Asking and Answering

今日は何曜日ですか？ Kyō wa nan'yōbi desu ka? What day of the week is today?

水曜日です。 Suiyōbi desu. It's Wednesday.

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Part 2: Months of the Year (〜月)

Japanese months are beautifully simple. Take the number (1–12) and add 月 (gatsu). That's it. No new words to memorize — if you know your numbers, you know the months.

Watch the Readings

Most are regular, but three months use specific number readings:

• April → しがつ (shi, not yon)
• July → しちがつ (shichi, not nana)
• September → くがつ (ku, not kyū)

These are the same irregular readings as telling time — 4, 7, and 9 are the troublemakers across all Japanese counters.

Asking and Answering

誕生日は何月ですか？ Tanjōbi wa nangatsu desu ka? What month is your birthday?

三月です。 Sangatsu desu. It's March.

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Part 3: Days of the Month (〜日)

This is the hard part. The days of the month from the 1st to the 10th use an ancient Japanese counting system (wago — 和語) that is completely irregular. After the 10th, things settle down — mostly.

The First Ten Days (Memorize These)

These don't follow any modern number pattern. They come from the native Japanese (yamato kotoba) counting system that predates Chinese-derived numbers. There's no shortcut — you just have to drill them.

A few things that might help:

• Most end in 〜か (ka), which is the native counter for days
• 一日 (tsuitachi) is the most irregular — it comes from 月立ち (tsukitachi — "the month stands/begins")
• 二日 through 十日 use the native numbers: ふた (2), み (3), よ (4), いつ (5), む (6), なな (7), よう (8), ここの (9), とお (10)

The 11th Through 31st

After the 10th, things get much easier. Most days use the standard Sino-Japanese number + にち (nichi):

The Remaining Irregulars

After the first ten, only three more days are irregular:

• 14th → じゅうよっか (keeps the よっか from the 4th)
• 20th → はつか (completely unique — from the native number for 20)
• 24th → にじゅうよっか (keeps the よっか again)

The pattern: anywhere a 4 appears in the ones digit, it uses よっか instead of にち. And 20 has its own special reading.

Asking and Answering

今日は何日ですか？ Kyō wa nannichi desu ka? What day of the month is it?

十五日です。 Jūgonichi desu. It's the 15th.

誕生日はいつですか？ Tanjōbi wa itsu desu ka? When is your birthday?

八月二十日です。 Hachigatsu hatsuka desu. It's August 20th.

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Part 4: Years (〜年)

Saying the Year

Years use 年 (nen). Say each digit of the year individually, then add 年:

In everyday speech, people often just say the last two digits for recent years:

二十五年 (nijūgonen) for 2025

The Japanese Era System (年号)

Japan also uses a traditional era system alongside the Western calendar. The era name changes when a new emperor ascends the throne:

So 2025 is also 令和7年 (Reiwa nananen). You'll see era years on government forms, official documents, coins, and expiration dates. Both systems are used — Western years for casual/international contexts, era years for official/traditional ones.

令和何年ですか？ Reiwa nannen desu ka? What year of Reiwa is it?

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Part 5: Counting Days, Weeks, Months, and Years

Beyond naming specific calendar items, you'll need to count durations — "three days," "two weeks," "six months." Each uses a different counter.

Counting Days (〜日間 or 〜日)

For durations, you can use 日間 (nichikan) or just 日 (nichi). The first ten days use the same native readings:

Important: "one day" as a duration is いちにち (ichinichi), NOT ついたち (tsuitachi). ついたち only means "the 1st of the month." This is the one place the readings differ.

三日間京都にいました。 Mikkakan Kyōto ni imashita. I was in Kyoto for three days.

Counting Weeks (〜週間)

Weeks use 週間 (shūkan). Perfectly regular — just number + 週間:

The only catch: 一週間 has a small っ — it's いっしゅうかん, not いちしゅうかん.

日本に二週間いました。 Nihon ni nishūkan imashita. I was in Japan for two weeks.

Counting Months (〜か月 or 〜ヶ月)

Month durations use か月 (kagetsu) — different from the month names (which use just 月):

Watch for double consonants: 一か月 → いっかげつ, 六か月 → ろっかげつ.

Written forms vary — you'll see か月, ヶ月, カ月, and 箇月. They all mean the same thing.

Don't confuse the two uses of 月:

• 三月 (sangatsu) = March (the month name)
• 三か月 (sankagetsu) = three months (a duration)

日本語を六か月勉強しました。 Nihongo o rokkagetsu benkyō shimashita. I studied Japanese for six months.

Counting Years (〜年間 or 〜年)

Year durations use 年 (nen) or 年間 (nenkan). Completely regular:

三年間日本に住んでいました。 Sannenkan Nihon ni sunde imashita. I lived in Japan for three years.

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Part 6: Useful Time Expressions

These words come up constantly when talking about the calendar:

Relative Days

Relative Weeks

Relative Months

Relative Years

Notice the pattern: 先 (previous), 今 (current), 来 (next) — the same prefixes work across weeks, months, and years. 去年 is the exception for "last year," though 先年 exists in formal writing.

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Part 7: Putting a Full Date Together

Japanese dates go from large to small: year → month → day (→ day of the week).

2025年7月1日（火曜日） Nisennijūgonen shichigatsu tsuitachi (kayōbi) Tuesday, July 1st, 2025

In conversation, you usually drop the year unless it's important:

七月一日に会いましょう。 Shichigatsu tsuitachi ni aimashō. Let's meet on July 1st.

The に particle marks specific dates, just like with clock times:

三月十四日に日本に行きます。 Sangatsu jūyokka ni Nihon ni ikimasu. I'm going to Japan on March 14th.

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Common Mistakes to Avoid

1. Mixing up month names and month durations

❌ 三月日本にいました。(Sangatsu Nihon ni imashita. — "I was in Japan in March" — not "for three months") ✅ 三か月日本にいました。(Sankagetsu Nihon ni imashita. — "I was in Japan for three months")

三月 = March. 三か月 = three months. The か月 makes all the difference.

2. Using ついたち for "one day" duration

❌ ついたちかかります。 ✅ いちにちかかります。(Ichinichi kakarimasu. — "It takes one day.")

ついたち = the 1st of the month. いちにち = one day (duration).

3. Forgetting the irregular days

❌ 四にち (yonnichi) ✅ よっか (yokka)

The first ten days and the 14th, 20th, and 24th are all irregular. There's no way around memorizing them.

4. Wrong readings for April, July, September

❌ よんがつ, なながつ, きゅうがつ ✅ しがつ, しちがつ, くがつ

Same trap as with hours — 4, 7, and 9 always use their alternate readings with 月.

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Practice

Try saying these dates aloud:

1. January 1st → ？
2. March 3rd → ？
3. May 5th → ？
4. July 20th → ？
5. December 24th → ？

Answers: いちがつついたち、さんがつみっか、ごがついつか、しちがつはつか、じゅうにがつにじゅうよっか

And these durations:

1. 3 days → ？
2. 2 weeks → ？
3. 6 months → ？
4. 1 year → ？

Answers: みっかかん、にしゅうかん、ろっかげつ、いちねん

The calendar system is one of those things that's hard at first but becomes automatic quickly — because you use it every single day.

毎日練習しましょう！ (Mainichi renshū shimashō!) — Let's practice every day!