Parashas Behar · Aliyah 1 · Passuk 25:11
Chabad.org — English translation + Rashi
Torah Temimah cites Rosh Hashanah 9a.
English: “It is a Yovel, the fiftieth year.” You count the fiftieth year and you do not count a fifty-first year; from here they said: the Yovel does not count toward the number of the shevu’a.
Classical derasha (Bavli Rosh Hashanah).
One counts the fiftieth year as the Yovel itself; the Yovel year is not included in the count of the next seven-year cycle.