The reckoning of the date of Easter

18 April 2019

Write, if you have any answers to the questions listed at the end of this section, or to add to the answers given below.


Why does the calendar reckoning of the date of Easter not always coincide with the ecclesiastical reckoning of the date? This year, the ecclesiastical date is 24 March, the first Sunday after the first full moon after the spring solstice, but the calendar date is 21 April.

Your answers: Finding the date of Easter can be a surprisingly complex calculation. Originally, Christians kept the date of the Jewish feast of Pesach (Passover), in which the dates of each month are linked to the lunar cycle and the year is kept synchronous with the seasons by the regular addition of a 13th month.

To simulate this, the First Council of Nicaea declared (well, the jury is still out on exactly what they declared) that Easter be kept on the Sunday after the full moon that falls on or after the March equinox (spring in the northern hemisphere, autumn in the southern). This reckoning includes the both the lunar and seasonal elements of the Hebrew calendar.

The link with the Roman and other solar calendars was to fix the said equinox to the date of 21 March. In reality, the equinox keeps slipping backwards in the calendar until we have a leap day that boots it back to 21 March.

In purely astronomical terms, the March equinox fell on Wednesday 20 March this year, and that date was also a full moon, which means that Easter could have been celebrated on Sunday 24 March if we agreed to use astronomical data. The practice, however, is that we fix the equinox to 21 March, making that full moon the day before meaningless.

That means that we have to wait until Thursday 18 April for the next full moon, putting Easter Day on the following Sunday, 21 April. The tabulated full moons of the Gregorian calendar are still almost always on the same day as actual full moons, owing to a clever set of corrections which was introduced by the German mathematician Christopher Clavius.

Some Eastern Churches retain the Julian calendar, which is now 13 days behind the Gregorian calendar. Almost all Eastern Churches, even if they use a reformed calendar for fixed feasts, retain the Julian calendar for computing the date of Easter.

The Julian equinox, fixed to 21 March, is on Gregorian 3 April. The unrevised full-moon table gives the date of 10 April for the full moon, which is Tuesday 23 April, leading to an Easter Day on Sunday 28 April, a whole week after that calculated in the Gregorian calendar.

(The Revd) Gareth Gilbert-Hughes (Precentor, St George’s Cathedral)
Perth, Western Australia


The history of the computation of the date of Easter is complicated; one of the best books on the topic is The Calendar, by David Ewing Duncan (Fourth Estate, 1998).

(The Revd) John Chamberlin
North Shields, Tyne and Wear


Your question: What exactly was Montanism, why was it condemned, and how does that relate to the Charismatic movement today?

K. L.


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