The most probable date for Good Friday is April 3, 33 AD. Isaac Newton figured that out in 1733.

Easter is that holiday that wanders around in the calendar and which you never quite know when will take place. Some get annoyed by that, but frankly I find it charming. But when did the crucifixion of Jesus really take place?

Questions like these were of much concern to Isaac Newton (1642-1726), surprisingly, since he is best known for gravitation and planetary orbits.

Newton was able to compute dates in year 33 and 34 AD when the crucifixion could have taken place. Others have also found that year 30 is a possibility.

Jewish holiday on a Friday

The timing of Good Friday is therefore much more concrete than that of the birth of Jesus. All we know is that if the birth can be timed by the star of Bethlehem, then it could have been an astronomical phenomenon in either one of the years 7, 6 or 5 BC, and that there is at least an uncertainty of a month each of these years. In contrast, Easter can be timed to the day.

Newton did that by combining two facts:

  • First, Jesus died the day before Passover, celebrated in memory of the exodus from Egypt. In Jewish culture it is called «pesach», and that word is reflected in the word for Easter in many languages («pâques» in French and variants of «påske» in Scandinavian languages). Easter is on the first Sunday following the first full moon after equinox, and this is very similar to how the time of pesach is found also.
  • Second, Good Friday took place on a particular day of the week, namely Friday. Combining this with the time for pesach, results in the dates that Newton computed.

Newton – much more than gravity

It is interesting that Newton was so concerned with this. After all, he has been made into the foremost symbol of the rational Newtonian universe which is like a clock that just keeps on going by itself.

It is less known that Newton left behind more than 2.5 million words about the Bible, theology, prophesy, and church history. It is in fact the topic which he wrote the most about. He was also very productive when it came to alchemy. Alchemy is something we tend to think only has to do with exotic production of gold, but Newton saw it as the key to understanding why some substances could have vitality and give rise to life.

Throughout history Newton has been interpreted and misused. In the century following his death, he was said to have suffered mentally after 1692 and that that explains the religious studies that we now find so strange. That is a handy way to explain them as an anomaly in contrast to his rational science.

But in light of the fact that he wrote about theology and the Bible throughout some 60 years, this is very unlikely. In addition it builds on a view of history where the past is interpreted primarily in light of the present.

Let Newton be Newton

I favor reading and understanding Newton based on his own premises. Historian of science Betty Jo Teeter Dobbs in her biography from 1991 emphasizes that for Newton there was but one truth, but that it could have several sources. It could be found in natural science, but also in alchemy, or in the revelation of God in the Bible.

What makes Newton so interesting is that he was concerned with much larger questions than most researchers are today. He wanted to explain the source of gravity, and he wanted to find out what life and consciousness was.

We know more about gravity today. We have Einstein’s general theory of relativity and we have quantum physics, talking about the curvature of space and a possible particle called a graviton. But these are primarily descriptions, not explanations. Neither have we come much further on the question of consciousness.

April 3, 33 AD

Newton himself concluded that Good Friday took place in 34 AD. Today this is considered to be too late, among others because Paul’s experience on the Damascus road most likely took place that year. Similarly the date in 30 AD is thought to be too early as it does not allow enough time for the three active years of the ministry of Jesus. Another moment in favor of 33 AD is that a lunar eclipse was visible from Jerusalem that day. There is justification in the Bible for saying that such an event could have happened on Good Friday.

This year’s Good Friday on April 3 therefore links Easter in a particular way to its origins. But remember, Newton was the first one to compute this date.


  • The Jewish calendar is both moon- and sun-based. Other calendars like the muslim one only follows the moon, while the Western one follows the sun.
  • Each month starts with new moon and Nisan, the first month of the year is linked to spring equinox.
  • Newton’s starting point was that the day before Passover, the 14. day of Nisan, always is on the first full moon after equinox.
  • He also discusses how the time of the new moon was determined from visibility in Jerusalem, and not from astronomical definitions. In this way he could find out when the 14. of Nisan fell on Fridays.
  • Humphrey and Waddington launched the theory of a lunar eclipse in 1983. They read Acts 2,20 (‘the moon will be turned to blood’) as a lunar eclipse on the day of the crucifixion.
  • John P. Pratt, "Newton's Date for the Crucifixion," Quarterly Journal of the Royal Astronomical Society, 1991.
  • Betty Jo Teeter Dobbs, The Janus Faces of Genius: The Role of Alchemy in Newton's Thought, Cambridge University Press, 1991.
  • Colin Humphreys and W. Graeme Waddington. "Crucifixion Date." Nature, 1990.

This is an expanded translation of the version in the Science section of the daily newspaper Aftenposten, April 2, 2015. Godfrey Kneller's portrait of Newton from 1689 is from Wikipedia Commons.