It is reported by Colladon (La vie de Calvin, d 7, Tome XXI, p76; in Translator's preface) that Calvin began these 159 sermons on February 26th, 1554. It is reported that the sermons on Job ended somewhere around March, with Calvin beginning a new biblical book, Deuteronomy, on March 20th, 1555.
A number of sources report that Calvin preached weekdays on Job, but only every other week, see for example Schreiner.
Further, it is reported that Calvin may have preached on the Wednesday's of the off week.
Lastly, and to add slightly more complexity, in Geneva in 1554 the Julian calendar was in use. The Julian calendar doesn't exactly line up with the modern Gregorian calendar and in 1554 the two calendars were separated by approximately 10 days.
Here is the Google Gemini prompt that I first used:
"Starting 26th February 1554 count forward 159 days but only counting weekdays, ignoring every other week apart from Wednesdays, ignoring all weekends, and tell me the final date. Do all of this using the Julian calendar that would have been used in Geneva in 1554."
The AI returns:
Based on the Julian calendar (which was in use in Geneva in 1554) and the specific counting rules provided:
The final date is Wednesday, February 27, 1555.
Calculation Details
Start Date: Monday, February 26, 1554. Rules Applied:
Week 1 (Active): Count Monday, Tuesday, Wednesday, Thursday, Friday. (5 counts)
Week 2 (Skip): Count Wednesday only. (1 count)
Cycle: This creates a repeating pattern of 6 counts every 2 weeks (14 days).
Counting Process:
Target: 159 counts.
Full Cycles: full cycles with a remainder of 3.Duration: 26 cycles 14 days = 364 days.Date after 364 days: 364 days is exactly 52 weeks. Starting from Monday, Feb 26, 1554, exactly 52 weeks later is Monday, February 25, 1555.Remaining Counts (3): We are now back at the start of an "Active" week (Week 53).Monday, Feb 25 (Count 157)Tuesday, Feb 26 (Count 158)Wednesday, Feb 27 (Count 159)The year 1555 in the Julian calendar is a standard common year (non-leap), so February has 28 days. The calculation fits perfectly within the calendar logic of the time.
I repeated the prompt but without the Wednesday during the off week
The final date is Thursday, May 09, 1555.
Based on the dates of the Deuteronomy sermons, the latter doesn't seem to work.
For observance of anniversaries we should convert the Julian calendar of 1554/1555 to the modern Gregorian calendar.
The date of February 26th, 1554 on the Julian calendar is Monday, March 8th, 1554 on the modern calendar. Below, all converted to the modern calendar, is a list of dates that the sermons were given on. I guess this serves to accurately recall anniversaries. For example on March 8th, 2026 the first sermon would have been given 472 years earlier to that day.
Sermon 1, Monday, March 08, 1554.
Sermon 2, Tuesday, March 09, 1554.
Sermon 3, Wednesday, March 10, 1554.
Sermon 4, Thursday, March 11, 1554.
Sermon 5, Friday, March 12, 1554.
Sermon 6, Wednesday, March 17, 1554.
Sermon 7, Monday, March 22, 1554.
Sermon 8, Tuesday, March 23, 1554.
Sermon 9, Wednesday, March 24, 1554.
Sermon 10, Thursday, March 25, 1554.
Sermon 11, Friday, March 26, 1554.
Sermon 12, Wednesday, March 31, 1554.
Sermon 13, Monday, April 05, 1554.
Sermon 14, Tuesday, April 06, 1554.
Sermon 15, Wednesday, April 07, 1554.
Sermon 16, Thursday, April 08, 1554.
Sermon 17, Friday, April 09, 1554.
Sermon 18, Wednesday, April 14, 1554.
Sermon 19, Monday, April 19, 1554.
Sermon 20, Tuesday, April 20, 1554.
Sermon 21, Wednesday, April 21, 1554.
Sermon 22, Thursday, April 22, 1554.
Sermon 23, Friday, April 23, 1554.
Sermon 24, Wednesday, April 28, 1554.
Sermon 25, Monday, May 03, 1554.
Sermon 26, Tuesday, May 04, 1554.
Sermon 27, Wednesday, May 05, 1554.
Sermon 28, Thursday, May 06, 1554.
Sermon 29, Friday, May 07, 1554.
Sermon 30, Wednesday, May 12, 1554.
Sermon 31, Monday, May 17, 1554.
Sermon 32, Tuesday, May 18, 1554.
Sermon 33, Wednesday, May 19, 1554.
Sermon 34, Thursday, May 20, 1554.
Sermon 35, Friday, May 21, 1554.
Sermon 36, Wednesday, May 26, 1554.
Sermon 37, Monday, May 31, 1554.
Sermon 38, Tuesday, June 01, 1554.
Sermon 39, Wednesday, June 02, 1554.
Sermon 40, Thursday, June 03, 1554.
Sermon 41, Friday, June 04, 1554.
Sermon 42, Wednesday, June 09, 1554.
Sermon 43, Monday, June 14, 1554.
Sermon 44, Tuesday, June 15, 1554.
Sermon 45, Wednesday, June 16, 1554.
Sermon 46, Thursday, June 17, 1554.
Sermon 47, Friday, June 18, 1554.
Sermon 48, Wednesday, June 23, 1554.
Sermon 49, Monday, June 28, 1554.
Sermon 50, Tuesday, June 29, 1554.
Sermon 51, Wednesday, June 30, 1554.
Sermon 52, Thursday, July 01, 1554.
Sermon 53, Friday, July 02, 1554.
Sermon 54, Wednesday, July 07, 1554.
Sermon 55, Monday, July 12, 1554.
Sermon 56, Tuesday, July 13, 1554.
Sermon 57, Wednesday, July 14, 1554.
Sermon 58, Thursday, July 15, 1554.
Sermon 59, Friday, July 16, 1554.
Sermon 60, Wednesday, July 21, 1554.
Sermon 61, Monday, July 26, 1554.
Sermon 62, Tuesday, July 27, 1554.
Sermon 63, Wednesday, July 28, 1554.
Sermon 64, Thursday, July 29, 1554.
Sermon 65, Friday, July 30, 1554.
Sermon 66, Wednesday, August 04, 1554.
Sermon 67, Monday, August 09, 1554.
Sermon 68, Tuesday, August 10, 1554.
Sermon 69, Wednesday, August 11, 1554.
Sermon 70, Thursday, August 12, 1554.
Sermon 71, Friday, August 13, 1554.
Sermon 72, Wednesday, August 18, 1554.
Sermon 73, Monday, August 23, 1554.
Sermon 74, Tuesday, August 24, 1554.
Sermon 75, Wednesday, August 25, 1554.
Sermon 76, Thursday, August 26, 1554.
Sermon 77, Friday, August 27, 1554.
Sermon 78, Wednesday, September 01, 1554.
Sermon 79, Monday, September 06, 1554.
Sermon 80, Tuesday, September 07, 1554.
Sermon 81, Wednesday, September 08, 1554.
Sermon 82, Thursday, September 09, 1554.
Sermon 83, Friday, September 10, 1554.
Sermon 84, Wednesday, September 15, 1554.
Sermon 85, Monday, September 20, 1554.
Sermon 86, Tuesday, September 21, 1554.
Sermon 87, Wednesday, September 22, 1554.
Sermon 88, Thursday, September 23, 1554.
Sermon 89, Friday, September 24, 1554.
Sermon 90, Wednesday, September 29, 1554.
Sermon 91, Monday, October 04, 1554.
Sermon 92, Tuesday, October 05, 1554.
Sermon 93, Wednesday, October 06, 1554.
Sermon 94, Thursday, October 07, 1554.
Sermon 95, Friday, October 08, 1554.
Sermon 96, Wednesday, October 13, 1554.
Sermon 97, Monday, October 18, 1554.
Sermon 98, Tuesday, October 19, 1554.
Sermon 99, Wednesday, October 20, 1554.
Sermon 100, Thursday, October 21, 1554.
Sermon 101, Friday, October 22, 1554.
Sermon 102, Wednesday, October 27, 1554.
Sermon 103, Monday, November 01, 1554.
Sermon 104, Tuesday, November 02, 1554.
Sermon 105, Wednesday, November 03, 1554.
Sermon 106, Thursday, November 04, 1554.
Sermon 107, Friday, November 05, 1554.
Sermon 108, Wednesday, November 10, 1554.
Sermon 109, Monday, November 15, 1554.
Sermon 110, Tuesday, November 16, 1554.
Sermon 111, Wednesday, November 17, 1554.
Sermon 112, Thursday, November 18, 1554.
Sermon 113, Friday, November 19, 1554.
Sermon 114, Wednesday, November 24, 1554.
Sermon 115, Monday, November 29, 1554.
Sermon 116, Tuesday, November 30, 1554.
Sermon 117, Wednesday, December 01, 1554.
Sermon 118, Thursday, December 02, 1554.
Sermon 119, Friday, December 03, 1554.
Sermon 120, Wednesday, December 08, 1554.
Sermon 121, Monday, December 13, 1554.
Sermon 122, Tuesday, December 14, 1554.
Sermon 123, Wednesday, December 15, 1554.
Sermon 124, Thursday, December 16, 1554.
Sermon 125, Friday, December 17, 1554.
Sermon 126, Wednesday, December 22, 1554.
Sermon 127, Monday, December 27, 1554.
Sermon 128, Tuesday, December 28, 1554.
Sermon 129, Wednesday, December 29, 1554.
Sermon 130, Thursday, December 30, 1554.
Sermon 131, Friday, December 31, 1554.
Sermon 132, Wednesday, January 05, 1555.
Sermon 133, Monday, January 10, 1555.
Sermon 134, Tuesday, January 11, 1555.
Sermon 135, Wednesday, January 12, 1555.
Sermon 136, Thursday, January 13, 1555.
Sermon 137, Friday, January 14, 1555.
Sermon 138, Wednesday, January 19, 1555.
Sermon 139, Monday, January 24, 1555.
Sermon 140, Tuesday, January 25, 1555.
Sermon 141, Wednesday, January 26, 1555.
Sermon 142, Thursday, January 27, 1555.
Sermon 143, Friday, January 28, 1555.
Sermon 144, Wednesday, February 02, 1555.
Sermon 145, Monday, February 07, 1555.
Sermon 146, Tuesday, February 08, 1555.
Sermon 147, Wednesday, February 09, 1555.
Sermon 148, Thursday, February 10, 1555.
Sermon 149, Friday, February 11, 1555.
Sermon 150, Wednesday, February 16, 1555.
Sermon 151, Monday, February 21, 1555.
Sermon 152, Tuesday, February 22, 1555.
Sermon 153, Wednesday, February 23, 1555.
Sermon 154, Thursday, February 24, 1555.
Sermon 155, Friday, February 25, 1555.
Sermon 156, Wednesday, March 02, 1555.
Sermon 157, Monday, March 07, 1555.
Sermon 158, Tuesday, March 08, 1555.
Sermon 159, Wednesday, March 09, 1555.