noun-modifying (irregular)
biennial; two-year
Used as a prenominal modifier meaning 'occurring every two years' or 'lasting two years'. Common in official contexts like plans, budgets, or contracts.
二か年計画を立てる。
We will draw up a two-year plan.
この植物は二か年周期で花を咲かせる。
This plant blooms on a biennial cycle.
Variant using Arabic numeral 2 instead of kanji 二.
Variant with Arabic numeral and small ヶ.
Variant with Arabic numeral and full-size カ.
Variant with Arabic numeral and small ヵ.
Uncommon variant with Arabic numeral and full-size ケ.
Rare variant with Arabic numeral and kanji 箇.
二年 is the simple 'two years' (duration or point in time), while 二か年 is a formal, prenominal modifier used in official contexts like 'two-year plan'.
Compound of 二 (two) + counter か (from 箇, a counter for items) + 年 (year). The か is often written as ヶ, カ, or ヵ, all derived from the kanji 箇.