Easter jumps around. Sure, it’s always on a Sunday, but unlike, say, the U.S.’s Labor Day (which always falls on the first Monday in September) Easter jumps around. It could be on the third Sunday in March. Or the fifth. Or the fourth. Or sometime in April. It jumps around. The dating of Easter comes from a combination of lunar and solar calendars, astronomical events, and religious tradition all crashing together. The result is that Easter is sometime in March. Or April. It’s complicated.

To help shed some light on when Easter is actually supposed to happen, we sat down with Jamie Jeffers, the man behind the excellent British History Podcast. Jeffers has previously gotten into some of the controversies surrounding Easter on his own show, and has detailed how fights over the holiday led to actual, real violence among early Christians. Also, there were some very bad haircuts involved. Again: It was complicated.

Pictured below: The Council of Nicea, which tried (tried) to sort this all out. They only kind of did.