Say someone's age: 〜歳 / 〜才

Mental Model: The Living Calendar of Age

In English, you can simply say “I'm twenty-five.” In Japanese, saying a bare number (*25です) sounds incomplete or ambiguous—as if you are announcing a locker number. You count human and animal age by attaching the counter suffix 〜歳(〜さい) (-sai) (or its common handwritten shortcut 〜才(〜さい) (-sai)) to the number.

Because さい begins with an s-sound, certain preceding numbers undergo sokuon contractions (the small っ) to prevent awkward mouth transitions:

• 1 year old: 一歳(いっさい) (issai) (contraction: *いちさい is ungrammatical).
• 8 years old: 八歳(はっさい) (hassai) (contraction: *はちさい is ungrammatical).
• 10 years old: 十歳(じゅっさい) (jussai) (or traditional 十歳(じっさい)).

The Adult Milestone: The Legend of 20 (二十歳)

When a person turns 20 in Japan, they reach the traditional legal age of adulthood and participate in 成人式(せいじんしき) (Coming of Age ceremonies). Instead of following regular number math (*にじゅっさい), 20 years old has its own historical, native Japanese reading:

• 20 years old: 二十歳(はたち) (hatachi)

Notice that はたち already contains the entire concept of “20 years old.” It never takes さい at the end—saying *はたちさい is an erroneous duplicate! (For ages beyond 20, regular numbering resumes: 21 is 二十一歳(にじゅういっさい) (nijuuissai), 28 is 二十八歳(にじゅうはっさい) (nijuuhassai)).

Asking Someone's Age: The Etiquette Ladder

Directly asking an adult their age can feel intrusive or blunt in Japanese society. Match your register to the relationship:

1. Casual / Close Friends & Children: - 何歳？(なんさい？) (nan sai?): “How old are you?” 2. Polite Standard (Peers & Younger People): - 何歳ですか？(なんさいですか？) (nan sai desu ka?): “How old are you?” 3. Respectful / Keigo (Adults, Customers, Strangers): - おいくつですか？: “May I ask your age?” - Uses the honorific prefix お plus the native counter いくつ. This softens the inquiry into an elegant, non-invasive question. In business settings, prepend 失礼ですが (excuse me, but...): 失礼ですが、おいくつですか？.