The Talmud records an argument as to when the new cycle begins. One opinion, the Rabbanim (Nedarim 61a, Rosh Hashanah 9a), explains that the yovel year stands alone, that it is not part of the 49 year cycle (shemitta years 7,14,21,28,35,42,49, yovel year 50). This means that year 51 begins a new cycle, shemitta years 57,64,71,78,85,92, 99, and the next yovel is year 100 . Year 101 begins a new cycle and year 150 is the third yovel year. With this system there are two consecutive years of not working the land, years 49 and 50, or years 99 and 100, etc., and the yovel year breaks up the seven year cycles of shemitta. This system is accepted by the Rambam (Laws of shemitta and yovel, 10:7) and Kawashima (2003).
The second opinion in the Talmud is Rabbi Judah ben Ilai (again Nedarim 61a and Rosh Hashanah 9a and Bergsma 2005) that the yovel year is part of the 49 year cycle. The idea is that the 50th year counts both as part of the previous cycle (shemitta years 7,14,21,28,35,42,49, yovel year 50) and is also part the first year of the next cycle (shemitta years 56,63,70,77,84,91,98, yovel year 99). With this cycle, year 99 is the second yovel year and begins the third cycle. The third yovel is year 148. This approach is similar to the first approach that there are two consecutive years of not working on the land (shemitta and yovel), but it differs from the first opinion since there are only 49 years from one yovel to the next and also there is no break in the counting of seven years of shemitta. However, as pointed out by the Talmud (Nedarim 61a), this approach is problematic since during the seven year cycle which includes a yovel year, the people can only work five years, while the Torah states that the people will work six years, and then rest in the seventh year, 25:3,4.
The Talmud in Nedarim notes that both opinions cannot explain verses 25:20-22, which record that the crops in the sixth year would be sufficient until the crops that are planted in the eighth year are reaped in the ninth year. The Torah is referring to the land lying completely fallow for only one year, but according to both opinions, there is a possibility that the land lies fallow for two years, when a yovel year follows a shemitta year, which would mean that the crops from the sixth year would have to last four years until the tenth year.
A third approach, which is possibly the opinion of R. Judah (in Talmud Rosh Hashanah 9a but not in Nedarim 61a), follows the second opinion that the yovel year is every 49 years, but maintains that the yovel year was also a shemitta year. The difference between the two approaches is that according to the second opinion the first year in the first cycle is a regular year, while according to the third opinion the first year in the first cycle was a special or shemitta year. According to third approach, the phrase in 25:2, "the land will rest, a Shabbat to G-d," is not a general statement, but indicating that the beginning of the count was a year of rest, though not necessarily a regular shemitta year. The next shemitta year would be year eight in the cycle and then the seventh shemitta year would be year fifty of the cycle, the yovel year, (shemitta years 8,15,22,29,36,43,50, yovel year 50) and the first year with regard to the count of the next fifty years (shemitta years 57,64,71,78,85,92,99, yovel year 99). Year 99 is 49 years from the previous yovel in year 50, and also the fiftieth year counting year 50 as the first year. The third cycle would be shemitta years 106,113,120,127,134,141,148 and yovel year 148. Again, year 148 is 49 years from the previous yovel year in year 99, and the fiftieth year counting year 99 as the first year in the cycle.
This approach accords with 25:20-22 since there are never two years when the land is not worked, and with 25:3,4 since there are always six years of work between each shemitta. In addition, this approach matches the counting by sefirat ha-omer in 23:15,16, that the first day that begins the count is a holiday, the offering of the omer sacrifice, and the fiftieth day, is also a holiday, Shavuot, and so too here the first and last years are shemitta and yovel years.
According to the third approach, why does the Torah (25:11) list the agricultural restrictions of the yovel year if in any event the year was a shemitta year? The answer is that had the restrictions not been motioned, then a person might have thought that the yovel year superseded the shemitta year, and there would be no restrictions in that particular shemitta year.
The most recent proponent that I saw of the third approach is Hye Kim (2010) and he makes the interesting point that this double counting (counting the same year, year 50, 99, 148, etc., as both the last year of one cycle and the first year of next cycle) accords with the counting in Shemot 19:10-11, Vayikra 7:16-19, and Vayikra 19:6,7.
In conclusion, the third approach best accords with the text.
Bibliography:
Hye Kim, Young, 2010, The Jubilee: Its reckoning
and inception day, Vetus Testamentum, 60, pp. 147-151.
Kawashima,
Robert, 2003, The Jubilee, every 49 or 50 years? Vetus Testamentum,
53:1, pp. 117-120.