Years and Age (年, 歳) | Japanese Grammar

Two counters carry the "years" side of Japanese time: 〜年（ねん） for years — both a year on the calendar and a stretch of years — and 〜歳（さい） for a person's age. 年 is one of the most cooperative counters in the language (it triggers almost no sound changes), which makes it a welcome breather after the chaos of 日 and 分. 歳 is nearly as tidy, with one glaring, culturally weighty exception: 二十歳はたち, "twenty years old," which every learner has to memorize as its own word.

Years: 〜年（ねん）

年 begins with the nasal n, and nasals shrug off both euphonic forces — so the counter itself never geminates or voices. All the variation comes from the number in front of it, and it's the familiar trio.

Years	Reading	Years	Reading
1年	いちねん (ichinen)	7年	ななねん (nananen)
2年	にねん (ninen)	8年	はちねん (hachinen)
3年	さんねん (sannen)	9年	きゅうねん (kyūnen)
4年	よねん (yonen)	10年	じゅうねん (jūnen)
5年	ごねん (gonen)	何年	なんねん (nannen)
6年	ろくねん (rokunen)

The one form to watch is 4年 = よねん — the 4 reads よ (as in 四時よじ), giving yonen, not yon-nen or shi-nen. For 7 and 9, the counting readings ななねん and きゅうねん are the everyday norm (you may hear しちねん and くねん, but they invite confusion and are avoided). 何年（なんねん） means both "what year?" and "how many years?"

この会社に入って四年になります。

kono kaisha ni haitte yonen ni narimasu

It's been four years since I joined this company.

日本に来て何年になりますか。

nihon ni kite nannen ni narimasu ka

How many years has it been since you came to Japan?

Calendar years vs. spans of years

Like 日 and 月, the 年 counter does double duty. As a calendar year, the number is just read as a full number plus 年: 2024年 is 二〇二四年 nisen-nijū-yonen (built on the large-number reading 二千二十四 — see Large Numbers: 万, 億, 兆). As a duration, 三年 means "three years"; add 間（かん）— 三年間 — to force the "for X years" reading.

父は二〇二四年に定年退職しました。

chichi wa nisen-nijū-yonen ni teinen taishoku shimashita

My father retired in 2024.

大阪で三年間働いてから、東京に戻りました。

ōsaka de sannenkan hataraite kara, tōkyō ni modorimashita

After working in Osaka for three years, I moved back to Tokyo.

Note the particle contrast, identical to dates and clock times: a calendar year is a point in time and takes に (二〇二四年に, "in 2024"); a span of years stands bare (三年間働いた, "worked for three years"). For a year-and-a-half, Japanese says 一年半 ichinen-han rather than 十八か月.

あと一年半で大学を卒業します。

ato ichinen-han de daigaku o sotsugyō shimasu

I graduate from university in another year and a half.

The era-year system: 令和, 平成, 昭和

Alongside the Western calendar, Japan runs an era system（和暦） you'll meet on official forms, coins, driver's licenses, and news. Each imperial era has a name, and years count from its start:

Era	Reading	Span
令和	れいわ (Reiwa)	2019 –
平成	へいせい (Heisei)	1989 – 2019
昭和	しょうわ (Shōwa)	1926 – 1989

So 2024 is 令和6年, read Reiwa roku-nen. The very first year of an era isn't 一年 but 元年（がんねん）, "the founding year": 2019 is 令和元年 Reiwa gannen.

免許証には令和六年って書いてあるよ。

menkyoshō ni wa reiwa roku-nen tte kaite aru yo

It says Reiwa 6 on the driver's license.

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You don't need to convert eras on the fly to survive — but recognizing 令和, 平成, 昭和 is essential for filling out any Japanese form, where the birth-year box often expects the era year, not the Western one. A quick anchor: 平成 began in 1989 and 令和 in 2019.

Age: 〜歳（さい）

A person's (or pet's) age uses 〜歳 sai. It begins with s, so it geminates after 1, 8, and 10, but is otherwise regular.

Age	Reading	Age	Reading
1歳	いっさい (issai)	8歳	はっさい (hassai)
2歳	にさい (nisai)	9歳	きゅうさい (kyūsai)
3歳	さんさい (sansai)	10歳	じゅっさい (jussai)
4歳	よんさい (yonsai)	20歳	はたち (hatachi)
5歳	ごさい (gosai)	何歳	なんさい (nansai)
6歳	ろくさい (rokusai)	おいくつ	o-ikutsu (polite)
7歳	ななさい (nanasai)

上の子は五歳で、下の子は一歳です。

ue no ko wa gosai de, shita no ko wa issai desu

The older child is five and the younger is one.

うちの犬はもう八歳になりました。

uchi no inu wa mō hassai ni narimashita

Our dog has already turned eight.

To ask an age, 何歳（なんさい）is neutral; おいくつ o-ikutsu is the polite version you'd use with someone older or a customer.

失礼ですが、おいくつですか。

shitsurei desu ga, o-ikutsu desu ka

Excuse me, may I ask how old you are?

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The kanji 歳 is often replaced by the simpler 才 on handwritten forms, signs, and children's worksheets (才 is far easier to write). They're read identically — さい — and mean the same thing here. 三才 and 三歳 are the same "three years old."

二十歳はたち — the reading with a birthday

The one age you cannot derive: 二十歳 is はたち hatachi, not ni-jū-sai. It's a fossil of the old native word はた ("twenty," the same root inside 二十日はつか, "the 20th"). And it carries cultural weight far beyond arithmetic: 二十歳 is the traditional threshold of adulthood, celebrated on 成人の日（せいじんのひ）, Coming-of-Age Day, in January. Even though Japan lowered the legal age of adulthood to 18 in 2022, はたち remains the emotionally significant "becoming an adult" number — and its special reading is a rite of passage learners are expected to know.

娘は来月で二十歳になります。

musume wa raigetsu de hatachi ni narimasu

My daughter turns twenty next month.

Crucially, only the bare 20 is はたち. The moment you add anything, it reverts to regular さい: 21歳 is にじゅういっさい ni-jū-issai, and 30歳 is さんじゅっさい san-jussai. はたち is a one-word island at exactly twenty.

Common mistakes

❌ 二十歳 = にじゅっさい

Incorrect — twenty years old has the special reading はたち.

✅ 二十歳 = はたち

hatachi

twenty years old

Ni-jussai is the reflex once you know the 歳 pattern, but 20 breaks it. It's はたち — memorize it the way you memorized ついたち for the 1st.

❌ 四年 = よんねん

Colloquially heard, but the standard reading is よねん.

✅ 四年 = よねん

yonen

four years

The 4 in 年 takes よ (giving yonen), matching 四時よじ. You'll hear yonnen casually, but よねん is the standard reading and the one used in 四年生 (yonensei, "fourth-year student").

❌ 一歳 = いちさい

Incorrect — 1 geminates before さい.

✅ 一歳 = いっさい

issai

one year old

歳 begins with s, so 1, 8, and 10 geminate: いっさい, はっさい, じゅっさい. A flat ichi-sai is a real pronunciation slip.

❌ 令和一年に生まれた。

Incorrect — the first year of an era is 元年 (がんねん), not 一年.

✅ 令和元年に生まれた。

reiwa gannen ni umareta

I was born in the first year of Reiwa (2019).

The opening year of any era is 元年 gannen, never 一年. This is fixed usage across every era name.

Key takeaways

〜年（ねん） counts years with no counter-side sound changes; the only number quirk is 4年よねん. 何年なんねん = "what year / how many years."
Calendar years take に (二〇二四年に); spans stand bare and can add 間 (三年間). A year-and-a-half is 一年半.
Recognize the eras 令和・平成・昭和 for forms; era year 1 is 元年（がんねん）.
〜歳／才（さい） states age; geminates after 1, 8, 10 (いっさい, はっさい, じゅっさい).
二十歳 = はたち is an irreducible, culturally loaded irregular — but 21 and up are regular さい again.

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