(For more on the subject of Yovel, click here to return to the Table of Contents.)
This is a commentary on the post "Rambam on the Year Count".
Let's start with Halachah 2. Am Yisrael left Mitzraim in 2448 after the birth of Adam HaRishon, entered Eretz Yisrael 40 years later in 2488, spent 14 years in conquering and dividing the land, leaving us in 2502. Therefore the next year, 2503, was the first to be counted towards Shmitah. If 2503 is the first year, then that makes 2509 the first Shmitah. However, the Rambam brings a chidush (per the GR"A there, see the Frankel edition of the Rambam here). It is 2503 from the birth of Adam HaRishon, which is the beginning of year 2, therefore if we are counting from Creation, we push everything back 1 year. The first Shmitah ever was in the year 2510.
Halachah 3 states that Am Yisrael counted 17 Yovels. They were not 17 complete Yovels. There were 16 complete 50 year periods, and another 36 years. That is to say 2503 is year 0, add on 16 * 50 = 800 years, and add another 36 years, and you arrive at the year 3339, the year the 1st Beit HaMikdash was destroyed, 1 year later than the Seder Olam Rabba brings, due to the different starting point.
Halachah 4 states that the 50 year cycle which started in 2504 ceased altogether in the year 3339, and for 70 years, there was no such cycle. Then we count the years following the building of the 2nd Beit HaMikdash in 3409, so 3409 is year 1. It was 7 years after that when Ezra arrived. The counting restarted the following year, since Shmitah and Yovel counting is from Rosh HaShanah (see the Radbaz there). Therefore the count for the 2nd Beit HaMikdash period started in the year 3416. The Rambam states that even though there was no Yovel during the period of the 2nd Beit HaMikdash, nonetheless, they counted the Yovel anyway.
Halachah 5 tries to resolve a difficulty. Our tradition says that both of the Batei Mikdash were destroyed in the year after Shmitah. The Rambam is basically saying that the 2nd Beit HaMikdash was destroyed during Shmitah, but since it was so close to Rosh HaShanah of the next year, it counts as being part of the next year.
Halachah 6 comes to tell us that if we were to continue the count of Shmitah and Yovel onwards, then the year that he is writing would be considered Shmitah, year 21 of the Yovel cycle.
Halachah 7 tells us that what we actually count is different from this; there is no 50 year cycle. Basically, when the Beit HaMikdash is not standing, we count only the 7 years of Shmitah, but not the 50 years of Yovel. This is a nafka minah. Yovel is only in full effect when the majority of Am Yisrael are in Eretz Yisrael, and the land is divided among the tribes (per the Yerushalmi Shvi'it chapter 10, and the Rambam). But we still count the cycle if the Beit HaMikdash is standing. If not, the cycle goes away altogether and there is only the 7-year cycle.
Halachah 8 shows us that when we get down to it, the cycle the Rambam brings is the same one that we keep today. If the Rambam tells us that 4936 is the year after Shmitah, then that means 4935 was Shmitah. 4935 / 7 = 705, an integer, just like this year 5768 / 7 = 824. It is not taught as a direct relationship with Creation but rather a count from the Destruction of the 2nd Beit HaMikdash. Nonetheless, the formula works. Shmitah Year = 3829 + 7n where 0 <= n <= 310.
According to what we do today, the year preceding Birkat HaChamah is always Shmitah. From the above, it would seem that there is no inherent relation between the two at all. The question remaining is what year does the Rambam hold we should use to make the brachah? No formula is given in Hilchot Brachot chapter 10.