Parashas Behar · Aliyah 7 · Passuk 25:50
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Kiddushin 20b.
English: “And he shall calculate with his purchaser.” This teaches that one calculates the years.
Classical derasha (Sifra / Bavli Kiddushin).
The redemption price is prorated according to the number of years remaining until Yovel, treating the service as the equivalent of a hired worker’s wages.