Intellectual cycle
The intellectual cycle is the longest of the three biorhythm cycles: 33 days from birth. The classic method links it to clarity, focus and the ability to decide. It stays in the high phase for about sixteen days and in the low phase for as many; the two crossings between them are its critical days.
It is the cycle added last: in the 1920s Alfred Teltscher, an engineer in Innsbruck, observed a 33-day periodicity in how students performed at exams. It has completed the classic trio ever since.
The 33-day rhythm was later rediscovered by Alfred Judt, a mathematician at the University of Bremen, who formalised its calculation tables, also cited in a NASA technical report on charting the cycles.
At 33 days it has no clean relationship with the week: it is four weeks and five days, so the critical day that marks the start of the cycle moves five weekdays on with every turn and returns to the same weekday only after seven cycles, that is 231 days. In the couple comparison it weighs mostly on communication and on decisions taken together.
For someone born on 15 June 1990, on 2 September 2026 the intellectual cycle is on day 29 of 33: in the second half, in the low phase, a few days from the end of the cycle.