On what date does Pesach fall?

Pesach begins on the 15th of Nisan (Vayikra 23:5–6). Like every Jewish day, it starts the evening before, so the festival begins on the night of the 14th going into the 15th. The 14th itself is Erev Pesach, the day the Pesach offering was brought in Temple times. Nisan always falls in spring, because the calendar adds a leap month when needed (Rambam, Hilchot Kiddush HaChodesh 4:1). That is why the Gregorian date changes every year.

In Israel Pesach lasts seven days. Outside Israel it lasts eight, because a second day of Yom Tov is kept in the diaspora (Shulchan Aruch, Orach Chaim 496:1–3).

Preparation starts before the festival. On the evening before the 14th (the night after the 13th of Nisan), chametz is searched for by candlelight (OC 431:1). On the morning of the 14th, eating chametz is forbidden from the end of the fourth halachic hour. Any chametz left over is burned or removed by the end of the fifth hour (OC 443:1). Chametz that will not be destroyed is usually sold through a rabbi (OC 448:3). The Seder matzah is eaten only after nightfall (OC 472:1).

A Beit Din may ask: when does Pesach start this year, how do you prepare your home, and what is the deadline for chametz on Erev Pesach?

A common mistake: thinking the chametz ban only starts at nightfall. In fact it starts on the morning of the 14th, hours before the Seder.