Why Does Easter Change Every Year? The Date Explained

Christmas is on 25 December. Halloween is on 31 October. Easter, meanwhile, turns up whenever it likes, or that's how it feels. In 2027 it falls on 28 March, which is early. In 2028 it's on 16 April. Some years schools break up with Easter weekend already behind them; other years it lands right in the middle of the holidays.

There is a rule behind it, though, and it's older and stranger than most people expect. Once you know it, you can roughly guess the date yourself.

The short answer

Easter is tied to the moon, not to a fixed day of the calendar.

In Western churches, Easter Sunday is the first Sunday after the first full moon on or after 21 March. That's it. Everything else is detail.

Because the moon runs on its own cycle of about 29.5 days, and Sunday can be anywhere from one to seven days after that full moon, the date can move by more than a month from one year to the next.

Where the rule comes from

Easter marks the resurrection, which the Gospels place around the Jewish festival of Passover. Passover is set by the Hebrew calendar, which follows the moon, so the earliest Christians tied Easter to the same lunar timing.

That caused arguments almost immediately. Some communities celebrated on the date of Passover itself, whatever day of the week it fell on. Others insisted it should always be a Sunday. The Council of Nicaea in 325 is often credited with settling the matter, and it did push churches to celebrate together, but it didn't actually write down a calculation. The method the Western church uses today was worked out in the following centuries, mainly from tables developed in Alexandria.

Why 21 March?

You might expect the rule to use the real spring equinox, the moment the sun crosses the equator. It doesn't. The church fixed the equinox at 21 March for the purposes of the calculation, even though the astronomical equinox usually happens on the 20th.

The same goes for the full moon. Easter isn't based on the full moon you can see in the sky. It uses an "ecclesiastical" full moon taken from tables, which is close to the real one but doesn't always match it to the day. That's why astronomers occasionally point out a year where Easter seems to break its own rule. It hasn't; it's just following the tables rather than the telescope.

The upside of fixing everything on paper is that anyone can work out Easter for any year without looking at the sky, and everyone gets the same answer.

The earliest and latest Easter can be

Put the pieces together and you get a window.

The earliest possible full moon is 21 March itself. If 21 March is a Saturday and also the full moon, Easter is the next day, 22 March. That's the earliest it can ever be, and it's rare. It last happened in 1818 and won't happen again before 2200.

The latest possible date is 25 April. That happens when a full moon falls just before 21 March, so you have to wait almost a whole lunar month for the next one, and then that one falls on a Sunday, pushing Easter on by another week. The last time Easter fell on 25 April was 1943, and the next time is 2038.

Most years land somewhere in the middle, from late March to mid-April.

Why Orthodox Easter is usually later

If you have friends or family in the Greek, Russian, Serbian or other Orthodox churches, you'll know their Easter often falls on a different Sunday, sometimes a week later, sometimes five.

That's because most Orthodox churches still calculate Easter using the old Julian calendar, which runs 13 days behind the Gregorian calendar most of the world now uses. They also use slightly different tables for the full moon. The rule is essentially the same, but it's being applied on a calendar that has drifted.

In 2027, for example, Western Easter is on 28 March but Orthodox Easter isn't until 2 May. In 2028 they line up, and both fall on 16 April. Over the long run the two dates coincide roughly three years in ten.

The knock-on effects

Because Easter moves, a whole run of other dates moves with it. Shrove Tuesday, or Pancake Day, is always 47 days before Easter Sunday, and Ash Wednesday is the day after that, which is why your pancakes are early one year and late the next. Good Friday and Easter Monday follow along, and so does Pentecost, seven weeks after Easter.

It also explains why the Easter school holidays don't always line up with the Easter weekend. Many schools fix their spring break to a set point in the term rather than chasing a date that can wander over five weeks.

Has anyone tried to fix the date?

Yes, more than once. In the UK, the Easter Act 1928 actually passed through Parliament. It would have fixed Easter as the Sunday after the second Saturday in April. It was never brought into force, because the government wanted the churches to agree first, and they never quite did.

Church leaders have discussed a common, fixed date many times since, partly to bring Western and Orthodox Christians together. Nothing has stuck. For now, the moon still decides.

Working it out yourself

If you want to estimate Easter for a given year, find the first full moon after 20 March in a moon calendar, then go to the following Sunday. You'll be right most of the time. For the exact date, check the church calendar, or our countdown to Easter Sunday 2027, which runs to the start of the day in UTC.

And if Easter seems early or late this year, it's not you. It's the moon.