Parashas Behar · Aliyah 5 · Passuk 25:29
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra / Arakhin 31a.
English: “Until the completion of the year of its sale.” A full year, and not a deficient year.
Classical derasha (Sifra / Bavli Arakhin).
The redemption period for a house in a walled city is a full twelve months from the day of sale.