Why does Easter's date change? Why it's different each year and how it's decided

Unlike other Christian holidays, Easter moves around from one year to the next.

While Christmas falls on the same day every year, Easter is what's known as a moveable feast.

It may seem strange to non-Christians, but there's a weird formula to when Easter falls every year and it's based on the moon.

To understand the moving date you have to go further back, to Passover. Jesus held the Last Supper with his disciples on the night of the Jewish festival of the Passover, he then died the next day, Good Friday.

He then rose on the third day, the Sunday.

The beginning of Passover is determined by the first full moon after vernal equinox.

When the Jews converted such dates still held importance.

So why does it move around?

The answer actual lies in a decision made several centuries after Christianity's inception.

In 325AD the Council of Nicaea established that Easter would be held on the first Sunday after the first full moon occurring on or after the vernal equinox.

There's a twist though; if a full moon falls on a Sunday, then Passover begins on a Sunday, so Easter is then delayed by a week to make sure it still occurs after Passover.

If you're still wondering why this doesn't fit, it's because the council fixed the date of vernal equinox at March 21, which is when it fell in 325AD though now it's March 20.