Counting the Omer begins on which day of Passover in rabbinic Judaism?

In rabbinic Judaism, Counting the Omer begins on the second day of Passover, the 16th day of Nisan.

The count connects Passover with Shavuot, which arrives after seven weeks. In the Temple period, the starting point was associated with presenting an omer—a sheaf or measure of newly harvested barley—as an offering. Rabbinic interpretation identifies the relevant date as the day after the first day of Passover, 16 Nisan.

Because Jewish days begin at sunset, the first Omer count is made on the second night of Passover. That evening begins the Jewish calendar date of 16 Nisan, even though part of the observance occurs before daylight. Each subsequent evening adds one day to the count.

This answer is specific to rabbinic Jewish practice. Karaite Judaism interprets the biblical phrase differently and begins counting on the day after the weekly Sabbath during Passover, so the date can differ. That distinction is why the question’s reference to rabbinic Judaism matters.