Why a conception chart is hard to time
In astrology, a chart cast for conception treats fertilization as the moment to map—not the later moment of birth. The difficulty is that fertilization usually cannot be observed directly. Sex and conception are not the same timestamp: sperm can remain capable of fertilization for several days, and an egg can be fertilized after ovulation. Knowing when intercourse occurred therefore does not establish the precise moment conception happened.
A disagreement about the starting point
Practitioners who favor conception charts must decide what counts as the chart’s starting instant and how precisely it can be known. Estimates based on cycle tracking or medical records may narrow a window, but they do not necessarily identify an exact minute. That leaves room for different judgments about which time to use—and, consequently, which chart to interpret.
The disagreement is more than a matter of preference: a chart depends on its timestamp, so changing the proposed moment can change its astrological details. For anyone trying this approach, the practical limit is clear: the birth time may be recorded, while the moment the chart requires may remain an estimate.
