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Why are Jewish holidays on different Gregorian dates each year?

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Circular diagram of the Jewish religious year showing Hebrew months around the outer ring and Gregorian months inside, with major holidays and fasts such as Rosh Hashanah, Yom Kippur, Sukkot, Hanukkah, Passover, and Purim labeled with their dates. — Jewish religious year The months and holidays of the Jewish religious year.

Jewish holidays fall on different Gregorian dates each year because the Jewish calendar is lunisolar, meaning it is regulated by the positions of both the Moon and the Sun.12

While the Gregorian calendar is a solar dating system, the Jewish calendar consists of 12 lunar months that total approximately 354 days. Because this is shorter than the solar year of about 365 1/4 days, the Jewish calendar must be adjusted to ensure that major festivals remain in their proper seasons.123

To maintain this alignment, a 13th month is periodically added in a leap year. This occurs seven times during every 19-year period, known as the Metonic cycle. Consequently, the number of days in a Jewish year can vary significantly—ranging from 353 to 385 days—which causes the dates of Jewish holidays to shift relative to the Gregorian calendar from year to year.1423