Map any year's Hebrew calendar to its Gregorian dates. Anchored to a chosen Passover, the tool calculates Nisan 1 from astronomical principles and overlays the Hebrew months on a familiar grid.
Enter a Passover date to find every year (11,013 BC – 2033 AD) with that same correct Passover
The two rules that determine the correct Passover date for any year
The anchor is March 31, 33 AD — a known Passover. Every other Passover is a whole number of lunar months away from that date. The math gives you two candidates each year — one before March 31 and one after, roughly 15 days either side.
But Passover by biblical law must fall in the month of Abib — the spring month. Spring begins at the vernal equinox, which the calendar fixes at March 21.
So the rule is: if a candidate date falls before March 21, spring hasn't arrived yet — which means it can't be Abib — which means it can't be Passover. It gets eliminated.
This one is pure astronomy. Passover is always the first full moon on or after the spring equinox. The two candidates the calculator gives you are always approximately one full lunar month apart — about 29.5 days.
So if both dates land after March 21, one of them is necessarily the first full moon after the equinox, and the other is the next full moon — already a whole month too late.
The date closest to March 21 is always the first qualifying full moon. The later one is the second. You always want the first.
Gregorian vs Hebrew months — note they overlap at different points in the year
Hebrew year begins in Tishri (civil) or Nisan (sacred/biblical). The Gregorian months above show approximate alignment — overlap shifts each year.