Parashas Behar · Aliyah 4 · Passuk 25:27
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra (Torat Kohanim).
English: “And he shall calculate the years of its sale.” This teaches that one calculates the years.
Classical derasha (Sifra).
The redemption price is prorated according to the number of years remaining until Yovel.