One and a half years — a period equal to a year plus half a year (18 months).
新しいプロジェクトは一年半かかる予定だ。
The new project is expected to take one and a half years.
彼女とは一年半ぶりに再会した。
I met her again after one and a half years.
その留学は１年半の予定です。
That study-abroad program is scheduled for one and a half years.