This weekend marks a kind of grand convergence of springtime religious holidays: Western and Orthodox Christians celebrate Easter on Sunday, which is also the sixth day of Passover. The phenomenon is not so unusual — the last time this happened was 2014 — but the holidays can sometimes differ by more than a month.

Passover is set by the Jewish calendar, beginning on the 15th day of Nisan, the first month of the Jewish sacred year. The rules for calculating the date of Easter are the same for the Western (Protestant and Roman Catholic) and Orthodox Christians: The holiday falls on the first Sunday after the first full moon after the spring equinox.

But the Orthodox and Western Christians use slightly different calendars and ways of determining the dates of the full moon and the vernal equinox, writes John Fotopoulos of St. Mary’s College in Indiana in the Public Orthodoxy blog of Fordham University’s Orthodox Christian Studies Center.

Justin Welby, the archbishop of Canterbury, said last year that he hoped to work out a universal Easter date with Pope Francis, the Coptic pope, and the ecumenical patriarch of the Orthodox church, according to a report in the Guardian.

The Rev. Demetrios Tonias, dean of the Annunciation Cathedral of Boston, said he and his Greek Orthodox colleagues sometimes wonder whether attendance will be down when the two Easters coincide, because many families celebrate both Easters.

But, he said with a laugh, “We were packed on Palm Sunday, so it really did not affect us at all this year.’’

Lisa Wangsness can be reached at lisa.wangsness@globe.com.