Counting the Omer
Question
I think I missed a day in the count...may I still recite the blessing?
Answer
Shalom!
Thank you for your question!
One who forgot to count Sefirah one night is to count anytime the next day until 13 and a half minuets from shekiah (sunset) but without reciting the blessing. One can then resume counting the next night with the blessings.
However, one who forgot to count for an entire 24 hr period is no longer permitted to count with a blessing. One should preferably hear the blessing from someone else and then respond “amen” before counting.
One who is unsure whether one counted a certain day or not is permitted to recite the blessing when counting the next night and thereafter.
On a related note, there is a debate among the poskim regarding one who knows in advance that he will miss one (or more) days of counting the Omer. According to some poskim, in such a situation one is not permitted to begin counting with a blessing at all in this case at all as some rishonim hold that one who misses one day of counting renders all his previous blessings as blessings in vain. Nevertheless, the halacha is that even such person may begin counting with a blessing.
SOURCES: OC 489:8; Mishna Berura 489:38; Kaf Hachaim 489:82; Minchas Yitzchak 9:57