A Summary of the Laws of Counting the Omer
There is a positive Torah commandment to begin counting the Omer from the day following the first day of Pesach for a duration of seven complete weeks. Nowadays when the Bet Hamikdash unfortunately no longer stands and we have neither the harvesting of the Omer nor the Omer offering, counting the Omer is no longer a Torah commandment and is only a rabbinic commandment. It is for this this reason that in the “Leshem Yichud” text recited before counting the Omer that one should not insert that this Mitzvah is a positive Torah commandment, for this is not so; rather, as we have written, this Mitzvah is merely rabbinic nowadays.
If one forgot to count the Omer for one complete day, one may no longer continue to count the Omer with a blessing; rather, one should continue to count albeit without a blessing.
If one is unsure if one forgot to count the Omer for a complete day, one may continue to count the Omer the following night (and all following nights as well) with a blessing.
The proper time for counting the Omer is at night. If one has forgotten to count the Omer at night, one should count during the day without reciting a blessing. Nevertheless, if one has done so, one may continue to count the Omer on all subsequent nights with a blessing.
Women are not obligated to count the Omer. Our custom is that women do not count the Omer at all (even without reciting a blessing). The reason for this is a Kabbalistic one. A woman who decides to count the Omer should make sure not to recite a blessing before doing so since she is exempt from this Mitzvah according to the letter of the law.