Counting the Omer
Question
If I tell someone the Sefira count before actually counting, am I still allowed to recite the blessing?
Answer
Shalom!
Thank you for your question.
If one is asked, after sunset, "What night of Sefirah is it tonight?" one should respond by saying "yesterday's count was such and such" (e.g. On the 4th night of Sefirah say "yesterday was the 3rd day of the Omer").
One who responded "tonight's is such and such" should recite after nightfall the sefirah without a bracha. This is true even if one did not complete the sentence with “...in the Omer.”
It is permitted, however to simply respond with a number as long as one does not say “today is.” Therefore, if one is asked, after sunset, "What night of Sefirah is it tonight?" one can answer “5.”
After the first week of counting, however, one is permitted to respond something like “today is 9” because one does not fulfill the mitzva unless one also says "...which is one week and 2 days.” Similarly, one is permitted to say on the night of the 33rd day of the Omer that "tonight is lag b'omer." however lechatchillah one shouldn't do so.
SOURCES: Mishna Berura 489:20, 21, 22; Sha'ar Hatziun 23, 26,28