The Gemara (Menachot 43b) states: “Rabbi Meir said: One must recite one hundred blessings every day.” The Rambam (Chapter 7 of Hilchot Tefillah), the Tur, and Maran Ha’Shulchan Aruch (Chapter 46) rule likewise. The Sefer Ha’Manhig (6a) writes: “We have a tradition as strong as a law brought down by Moshe Rabbeinu from Mount Sinai that we are required to recite one hundred blessings every day and this is based on the Torah, Prophets, and Scriptures.” He proceeds to explain how this law is derived from every portion of Tanach.
Our Sages teach us that when King David was notified that one hundred people were dying in Jerusalem every day, he saw through Hashem’s holy spirit and enacted that one hundred must be recited every day. The Midrash states that from the time of David’s enactment to recite one hundred blessings, the plague in Jerusalem halted. Rabbeinu Bechaye writes in his Sefer Kad Ha’Kemach that Moshe Rabbeinu actually enacted that the Jewish nation recite one hundred blessings daily.
Clearly, all this means is that one should not recite less than one hundred blessings every day; however, one may certainly recite more than one hundred blessings every day. On the contrary, anyone who recites a blessing in the correct place performs a Mitzvah.
Thus, every individual should make a personal calculation in order to ascertain if one indeed meets the required quota of one hundred blessings. However, this is not so difficult at all taking into consideration the Morning Blessings (Birkot Ha’Shachar), the Blessings on the Torah, the Blessings of Keri’at Shema, the Amida prayer, and all other blessings we recite throughout the day. (Women can certainly meet this quota of one hundred blessings a day with the blessings of the Amida, Blessings of Enjoyment on foods, and Birkat Hamazon.)
Even on Shabbat when several blessings are missing as a result of the shortened Amida prayer (on weekdays, every Amida prayer consists of nineteen blessings while on Shabbat, each Amida prayer consists merely of seven; however, Mussaf is added and this too consist of seven blessings), one must nevertheless complete one hundred blessings. One should take care to do so by reciting blessings on fragrant smelling objects, fruits, and other sweets, as the Gemara (ibid.) tells us that Rabbi Chiya son of Rabbi Aviya would do so on Shabbat and Yom Tov in order to complete the required one hundred blessings. One should at least try to fulfill one’s obligation by answering Amen on all of the Blessings of the Torah recited before and after the reading of each Aliya of the weekly Torah portion, for each Amen answered can likewise be considered its own blessing.
Indeed, Maran Rabbeinu Ovadia Yosef zt”l was especially careful regarding this law and every Shabbat, he would count his blessings in order to complete the one hundred required blessings by reciting blessings on fragrant herbs and the like. He would make sure to do so on Yom Kippur as well. Every single blessing was like a jewel in his eyes and he would recite it with great care and concentration. Although he is no longer with us physically, let us learn from his great ways and aspire to emulate him as much as possible.
Summary: One is obligated to recite one hundred blessings every day. If one cannot meet this quota by actually reciting one hundred blessings on his own, one should at least try to do so by answering Amen to the Blessings of the Torah and other blessings one hears.