BoomClock/Holidays/Easter

When Is Easter?

Why does Easter move every year?

Because Easter is the only major holiday tied to the Moon rather than the calendar. Christmas is a number. Thanksgiving is a weekday rule. Easter is an astronomical event filtered through a 1,700-year-old calculation, and it can land on any of 35 different dates, from March 22 to April 25.

You have probably seen the rule stated like this: Easter is the first Sunday after the first full moon following the spring equinox. That sentence is wrong twice, and the two errors are the whole reason the date is hard to predict in your head.

Error one: it is not the real equinox

The calculation uses March 21, fixed, forever. The actual astronomical equinox wanders between March 19 and March 21 depending on the year. The church pinned it to a date and stopped caring what the sky does.

Error two: it is not the real full moon

The "full moon" in the rule is the paschal full moon, which is not a moon at all. It is a moon from a table: a theoretical moon derived from a repeating cycle, which can differ from the one you would actually see by a day or two.

This was deliberate, and it is the part worth admiring. If Easter depended on observing the moon, then cloud cover in one city and clear skies in another would put Christendom on different Sundays. By computing a fictional moon that everyone could agree on in advance, the church bought certainty at the price of accuracy. Every church, everywhere, could calculate the same answer for any year, centuries ahead, without looking up once.

So the honest version of the rule is: the first Sunday after the first ecclesiastical full moon falling on or after a fixed March 21. Less catchy. Actually correct.

The computus

The calculation has its own name, computus, and for centuries it was one of the most important problems in European mathematics. Working out Easter was a genuine intellectual industry: it drove the study of arithmetic and astronomy in medieval monasteries, and it is a large part of why the church cared about calendars at all.

Its engine is the Metonic cycle, named for the Greek astronomer Meton, who noticed around 432 BC that the phases of the Moon repeat almost exactly every 19 years: 235 lunar months land within about two hours of 19 solar years. That near-coincidence is what makes a lunar calendar predictable with nothing but integers, and the whole of Easter dating hangs off it.

The First Council of Nicaea in 325 AD is usually credited with setting the rule. What it actually did was narrower and more political: it ruled that all churches should celebrate the Resurrection on the same day, and independently of the Jewish calendar. It did not publish a method. The arithmetic everyone now uses was hammered out afterwards, over centuries of disagreement.

Easter's date range, and its extremes

Easter can fall on any Sunday from March 22 to April 25. Both ends are genuinely rare, and the numbers are more striking than the rule suggests:

• March 22, the earliest possible Easter, last happened in 1818. It will not happen again until 2285. Nobody alive has seen one, and nobody alive will.
• April 25, the latest possible, last happened in 1943 and comes round again in 2038, which is close enough to plan for.

Curious what weekday any other date falls on? Our day-of-the-week calculator covers any date from 1900 onward.

Why is Orthodox Easter on a different date?

Same rule. Different calendar. Orthodox churches apply the same "first Sunday after the paschal full moon on or after March 21" logic, but they run it on the old Julian calendar, whose March 21 currently arrives 13 days later than the Gregorian one, and whose moon tables have drifted further still.

The result is not a fixed offset, which is what makes it interesting. Sometimes the two Easters land on the same day. Sometimes they are a week apart. Occasionally they are five weeks apart, which is exactly what happens in 2027: Western Easter falls on March 28 while Orthodox Easter is not until May 2. That 35-day gap is the widest the two systems can produce.

Frequently asked questions

When is Easter?

Easter moves every year. The date is at the top of this page.

How many days until Easter?

The live counter at the top of this page has the exact figure.

Why does Easter change every year?

Because it is set by the Moon, not the calendar: the first Sunday after the ecclesiastical full moon that falls on or after a fixed March 21. Since lunar months do not divide evenly into the solar year, the date moves within a 35-day window.

What is the earliest and latest Easter can be?

March 22 at the earliest and April 25 at the latest. March 22 last occurred in 1818 and next occurs in 2285. April 25 last occurred in 1943 and next occurs in 2038.

Why is Orthodox Easter different?

Orthodox churches use the same rule on the Julian calendar, which now runs 13 days behind the Gregorian one. The two Easters sometimes coincide, and can be up to five weeks apart.

Is Easter always on a Sunday?

Yes, by definition. The rule selects a Sunday, so Easter can never fall on any other day. Good Friday is always two days before, and Easter Monday the day after.

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