counter
Used in formal or written contexts to count years, often in contracts, plans, or official documents. Equivalent to 年間 but more formal.
この計画は５カ年で完了する予定です。
This plan is scheduled to be completed in five years.
３カ年契約を結びました。
We signed a three-year contract.
Variant with small katakana ヵ; visually similar to カ.
Variant using the small ke character ヶ, often read as か in counters.
Full-size katakana ケ; less common and may be confused with ケ (ke).
年間 is the common, everyday counter for years. カ年 is more formal and often used in official documents.
Combination of the counter prefix カ (abbreviation of 箇/個) and 年 (year). The カ derives from the first character of 箇, used as a generic counter.