The Omer period lasts 49 counted days, or seven complete weeks, beginning during Passover and ending before Shavuot.
In rabbinic Judaism, the first day is counted on 16 Nisan, the second day of Passover. Participants then count each successive day aloud, often stating both the total number of days and the number of weeks plus days. The 49th day is the final day of the count; Shavuot follows as the 50th day in the sequence.
The period takes its name from the omer offering, a sheaf or measure of newly harvested barley that was presented in the Jerusalem Temple. The offering marked the beginning of the new grain harvest and the start of the count. Although the Temple offerings ceased after the Second Temple’s destruction, Jewish communities continue the counting as a religious practice.
A frequent mistake is answering 50 because Shavuot is sometimes described as occurring 50 days after Passover. The count itself contains 49 days; Shavuot is the festival reached after those seven weeks.