Easter Date Calculator — Western and Orthodox, for any year

The Easter date calculator above implements the ecclesiastical computus — the rule the churches actually use — in both of its surviving forms. The Western date comes from the Gregorian computus in the anonymous algorithm published in Nature in 1876 and reproduced in Jean Meeus’s Astronomical Algorithms. The Orthodox date comes from the Julian computus, computed on the Julian calendar and then converted to the Gregorian calendar for display.

Arb Digital builds free calculators that name the method they run and show their working. Easter is a good example of why that matters: two entirely correct calculations give different answers in most years, and a tool that reports one without saying which is not much use to anyone trying to reconcile a diary.

What This Easter Date Calculator Does

It computes both Easters for a year you choose, reports the gap between them in days, and derives the movable feasts that are defined by their offset from Easter. It also prints a short table of upcoming years, because that is what most people actually came for.

The Orthodox date is shown on the Gregorian calendar — that is, on the calendar your diary and your phone use. This is a real source of confusion. The Julian computus produces a date on the Julian calendar, which is currently thirteen days behind the Gregorian one. Orthodox Easter in 2026 falls on 30 March by Julian reckoning, which is 12 April on the civil calendar, and it is the second of those two numbers that tells you which Sunday it actually is.

The feast offsets are fixed and identical in both traditions, so the same set of days moves as a block. Ash Wednesday is 46 days before Easter, Palm Sunday 7 days before, Good Friday 2 days before, Ascension 39 days after and Pentecost 49 days after.

How to Use It

1. Type a year. The field opens on the current year and accepts anything from 1583 to 4099.
2. Read the hero for the Western date and the first grid item for the Orthodox one. The difference is always a whole number of weeks.
3. Switch the feast selector if you want Lent and Pentecost counted from the Orthodox date instead.
4. Change the number of years to list if you are planning further ahead than the default decade.
5. Use the “This Year” button to jump back to the current year at any point.

The Rule Behind the Calculation

Easter is the first Sunday after the first full moon on or after the spring equinox. That sentence is almost right, and the two places it is wrong are the whole difficulty. As the Royal Observatory explains in its account of when Easter falls, the equinox used is not the true astronomical equinox but a fixed convention of 21 March, and the full moon used is not the true full moon but an ecclesiastical one derived from the 19-year Metonic cycle.

That is why the date can be computed centuries ahead with pen and paper: it depends on arithmetic tables rather than on observation. It is also why the calculated Easter occasionally differs from what an astronomer would predict from the real moon. The rule is a convention, agreed for the purpose of everyone keeping the same feast, not a description of the sky.

The IMCCE at the Paris Observatory publishes an account of the same machinery — the golden number, the epact, the dominical letter — in its explanation of the astronomical calculation of the Easter date, covering both the Julian computus used until 1582 and the Gregorian one used since 1583.

The Formula: How It Is Calculated

The Gregorian computus used here is the anonymous algorithm of 1876. With Y as the year, it computes a = Y mod 19, b = ⌊Y/100⌋, c = Y mod 100, d = ⌊b/4⌋, e = b mod 4, f = ⌊(b+8)/25⌋, g = ⌊(b−f+1)/3⌋, h = (19a + b − d − g + 15) mod 30, i = ⌊c/4⌋, k = c mod 4, L = (32 + 2e + 2i − h − k) mod 7, and m = ⌊(a + 11h + 22L)/451⌋. The month is ⌊(h + L − 7m + 114)/31⌋ and the day is ((h + L − 7m + 114) mod 31) + 1.

The Julian computus is shorter: a = Y mod 4, b = Y mod 7, c = Y mod 19, d = (19c + 15) mod 30, e = (2a + 4b − d + 34) mod 7, month = ⌊(d + e + 114)/31⌋, day = ((d + e + 114) mod 31) + 1. That result is a Julian calendar date, which this page converts to the Gregorian calendar through the Julian day number before displaying it.

Work through 2026. In the Gregorian algorithm a = 12, b = 20, c = 26, d = 5, e = 0, f = 1, g = 6, h = 12, i = 6, k = 2, L = 2 and m = 0, so the month is ⌊128/31⌋ = 4 and the day is (128 mod 31) + 1 = 4 + 1, giving 5 April 2026. The Julian computus for the same year gives 30 March on the Julian calendar, which is 12 April 2026 on the civil calendar, one week later.

The implementation was checked against published dates for eleven years before shipping: 1943, 1961, 2000, 2010, 2020, 2021, 2024, 2025, 2026, 2027 and 2030. Both branches matched in every case, including the years the two traditions coincide (1943, 2010 and 2025) and the year they are furthest apart in that sample (2024, where Western Easter is 31 March and Orthodox Easter is 5 May, a gap of five weeks).

Why the Two Dates Differ, and by How Much

Both traditions use the same rule. The difference comes from two separate disagreements, and they interact.

The first is the calendar. The Orthodox calculation places its notional 21 March equinox on the Julian calendar, which currently corresponds to 3 April on the Gregorian one. So the Orthodox Easter cannot fall before that later date, which alone pushes it later in most years.

The second is the lunar table. The Gregorian reform adjusted the Metonic cycle to keep the ecclesiastical moon in step with the real one; the Julian computus kept the original table, which has drifted by several days over the centuries. The two therefore identify different paschal full moons in many years.

Because both then take the following Sunday, the gap is always a whole number of weeks: zero, one, four or five. It is never two or three, which surprises people, and it is a direct consequence of both calculations landing on Sundays. In the sample above, 2025 gives a gap of zero, 2026 gives one week, 2027 gives five and 2021 gives four.

The Range of Possible Easter Dates

Gregorian Easter can fall on any date from 22 March to 25 April inclusive, a window of 35 days. The extremes are genuinely rare: 22 March last occurred in 1818 and will not recur until 2285, and 25 April last occurred in 1943 and next occurs in 2038. The most common dates cluster in early to mid April, which is why the season feels less variable than the 35-day window suggests.

That 35-day spread is the reason so much of the year moves. School terms, public holidays in many countries, and the entire Lenten and Pentecost cycle are pinned to it. If you need to know how many days sit between this year’s Easter and next year’s, or between Easter and some other fixed event, our date difference calculator will count them, and the add days to date calculator will apply any offset you like to a date the page gives you.

One consequence worth knowing: because the Gregorian Easter cycle repeats exactly every 5,700,000 years, and because leap year rules interact with the lunar corrections, there is no short repeating pattern you can memorise. The arithmetic really is the shortest route to the answer.

What This Calculator Is Not

It is not an astronomical moon calculator. The ecclesiastical full moon it uses is a table entry, not an observation, and it can differ from the real full moon by a day or two. If you want the actual lunar phase for a date, our moon phase calculator does that job and will occasionally disagree with the computus, correctly.

It is also not a historical calendar tool for the years before the Gregorian reform. Before 1583 there is only one computus, the Julian one, and the civil calendar in use was the Julian calendar too, so converting the result to Gregorian dates would be misleading. The year field starts at 1583 for that reason.

And it takes no position on the long-running proposals to fix Easter to a common date. Several have been floated over the last century and none has been adopted; the calculator reports what the rules currently in force produce. For simpler date questions, the day of week calculator and the leap year calculator handle the underlying calendar arithmetic directly.

Common Mistakes to Avoid

• Using the real full moon. The rule uses an ecclesiastical moon from a fixed table, which can differ from the astronomical one by a day or more, and that difference occasionally moves Easter by a whole week.
• Reporting Orthodox Easter as a Julian date. A Julian calendar date is currently thirteen days behind the civil one. Quoting it unconverted puts the feast on the wrong Sunday.
• Assuming the gap can be any number of weeks. It is always zero, one, four or five, because both calculations land on a Sunday.
• Applying the Gregorian algorithm before 1583. It does not describe any calendar that was in use, so the answer is meaningless rather than merely wrong.
• Expecting a repeating pattern. The full Gregorian Easter cycle is 5.7 million years long. There is no short rule of thumb hiding behind the arithmetic.

Related Free Tools From Arb Digital

Count forward or back from any Easter with the add days to date calculator, measure the gap to another event with the date difference calculator, or count down with the days until date calculator — that last one needs a date supplied to it, which is exactly what this page derives. For the underlying calendar mechanics, the day of week calculator and the leap year calculator are the direct tools, and the moon phase calculator gives you the astronomical moon the computus deliberately approximates. Everything else is on the free online tools hub.

Frequently Asked Questions

This page runs a published ecclesiastical rule, not an astronomical one. The equinox and full moon it uses are fixed conventions rather than observations, and individual churches and jurisdictions may in practice observe local variations, so confirm any date that matters against the calendar of the tradition concerned.