• Easter falls on a different date every year.
• This is because it is determined by the Jewish calendar, which is based on lunar cycles.
• Here’s how to work out when Easter will fall every year.

Do you ever feel like Easter comes out of nowhere?

Maybe you didn’t realise, but the Easter weekend actually falls on a different date every year, any time between March 22 and April 25. This year Easter Sunday is April 1.

As a Christian holiday, you might expect it to have a set date like Christmas. However, Easter is actually determined by the Jewish calendar. This is because in the Bible, the death, burial, and resurrection of Jesus Christ happened after the Jewish festival of Passover, and followers wanted it to be celebrated as such.

However, this is slightly tricky because the Jewish calendar is based on lunar cycles, whereas Christian culture is based on the sun. A solar year is just over 365 days and a lunar year is about 354 days, so collaborating the two can be complicated.

Passover also changes every year, because it’s calculated by the first full moon following something called the vernal equinox — a day in spring when night and day are exactly the same length.

An article on ThoughtCo says that in the early days of the Christian Church, Easter would fall on the first Sunday immediately after the vernal equinox. However, to establish a more standardised system, in 1583 a table was recorded by astronomers to determine all the future Ecclesiastical full moons. These land on the 14th day of the lunar month.

Ever since 1583, the Passover full moon — or Paschal full moon— has been determined from these historical tables, and is the first full moon date after March 20. Easter is always celebrated on the Sunday immediately following it, so as a result, it no longer directly corresponds to the moon.

The Paschal full moon can vary as much as two days from the date of the actual full moon. This is why the dates can range from March 21 to April 18, and Easter falls between March 22 to April 25 in Western Christianity.

This year, March has two full moons. One was on March 1, and the second will be on March 31. The first Sunday after the second moon is the next day, April 1, which is thus Easter Sunday this year.

There is a mathematical method for working out the date of Easter too — between the years 1900 to 2199. Here it is:

1. First, divide the year by the number 19.

E.g.: 2018 / 19 = 106.21

2. Multiply the number before the decimal point by 19.

E.g.: 106 x 19 = 2014

3. Subtract step 2 from the original year.

E.g.: 2018 – 2014 = 4

4. Add 1.

E.g.: 4 + 1 = 5

5. Look up this number in the following list (5), and Easter is on the first Sunday after the date given.

0 — March 27

1 — April 14

2 — April 3

3 — March 23

4 — April 11

5 — March 31

6 — April 18

7 — April 8

8 — March 28

9 — April 16

10 — April 5

11 — March 25

12 — April 13

13 — April 2

14 — March 22

Number 5 corresponds to March 31, and the Sunday after this date is April 1, which is Easter Sunday.