The verse from Leviticus cited above states: “Seven weeks; they shall be complete,” which is understood to mean that each day should be entirely included in the count. In order for this to be accomplished, it is preferable for the counting to take place at the beginning of the night, which is about half an hour after sunset. For those who pray the evening service in the synagogue, the counting is done immediately after the evening prayers. Nevertheless, one who forgot to count at the beginning of the night may do so all night, with the blessing, and he may even count throughout the following day until sunset, albeit without reciting the blessing (see below).

Before counting the omer at night, one recites the following blessing:

“Blessed are You, Lord our God, King of the universe, who sanctified us through His commandments, and commanded us concerning the counting of the omer.”

Before the blessing and the counting, some have the custom to recite the formula of Leshem yihud (“For the sake of the unification”), in preparation for the fulfillment of the mitzva. This passage can be found in prayer books.

As cited above, the Torah states: “You shall count fifty days.” In another verse, the Torah states: “You shall count seven weeks for you” (Deuteronomy 16:9). Taken together, these verses indicate that one must count both the days and the weeks. Therefore, the counting is performed in a manner that combines the two requirements. On the first day one says: “Today is one day of the omer,” and on the next day: “Today is two days of the omer,” and so on. When one reaches the seventh day, he begins to add the number of weeks: “Today is seven days, which are one week, of the omer.” From the eighth day onward, one first counts the number of days and then the number of weeks that have passed plus the days that have been added to the present week: “Today is eight days, which are one week and one day, of the omer.” The same pattern continues for each of the subsequent days. Following is an example of how to count the thirty-first day:

“Today is thirty-one days, which are four weeks and three days, in the omer.”

Sephardim use a slightly different formula:

“Today is thirty-one days of the omer, which are four weeks and three days.”

This is the correct way to count the omer. Nevertheless, if one specified the right number of days, even if he did not mention the number of weeks, he has still fulfilled the mitzva. If one counts in any language, he has fulfilled the mitzva, provided that he understands that language. One who counts in a language that he does not understand, even if he says the full formula in the exact manner, has not fulfilled the mitzva.

After the counting, there are those who have the custom to recite various additional prayers, some of which are based on the Kabbala. These can be found in prayer books.

Further reading: For more on counting the weeks, see A Concise Guide to Mahshava, p. 100.

One who forgot or did not have a chance to count the omer at night should count during the ensuing day, but without reciting the blessing. If he neglected to count one of the days completely, not having counted at night or during the ensuing day, there are halakhic authorities who maintain that from that point onward he may no longer continue counting. Their reasoning is that the forty-nine days of counting the omer are a single mitzva, which means that if one day is missing from the count, the entire mitzva is unfulfilled.

According to a different opinion in halakha, each day of counting the omer is a separate, independent mitzva, and therefore, even if an entire day is missed, one can and should continue to count the following days with the blessing. Since this is subject to dispute, one should continue counting, but without reciting the blessing. It is best for a person in this situation to listen to the blessing of the prayer leader in the synagogue, or to someone else who is reciting the blessing, to intend to fulfill his own obligation with this blessing, and respond: Amen, before counting for himself.

If one is uncertain as to whether or not he counted on a given day, he should continue to count on the following days with a blessing.

During the Temple period, the omer offering was brought on the first day of the counting, the sixteenth of Nisan, which is the first day of the intermediate days of Passover in Israel. The first harvested barley sheaf was brought to the Temple as a sacrifice together with an accompanying animal offering. This act served to permit the consumption of that year’s new produce, which could not be eaten before the omer offering was brought (Leviticus 23:14). The term “new produce,” or, in Hebrew, hadash, refers to grain that took root after the omer offering of the previous year.

Even today, when there is no omer offering, it is prohibited to eat grain from the new produce of the year until the end of the second day of Passover. In Israel, the Chief Rabbinate does not give kosher certification to any product that contains grain that is hadash. Outside of Israel, most organizations that certify products as kosher do not concern themselves with the possible presence of hadash grain, relying on the fact that most of the grain in the market is not hadash, and that according to some authorities this prohibition does not apply to grain grown outside of Israel. However, some are careful to eat only products that are known not to contain any hadash grain; such products are called yashan (literally, “old”).

Further reading: For more on the omer offering, see A Concise Guide to the Torah, p. 316; A Concise Guide to the Sages, p. 158.