Part of Fortune Calculator

The Part of Fortune, or Lot of Fortune, is the oldest and most used of the Arabic parts - a family of calculated points that Hellenistic astrology derived by measuring the distance between two placements and projecting it from a third. Fortune takes the arc between the Sun and the Moon and lays it off from the ascendant, which means it marks where the horizon would have fallen if the Moon had been where the Sun was. Astrologers read it as the place where things come easily: flourishing, physical wellbeing, and the area of life where effort tends to be repaid.

The formula reverses between a day birth and a night birth, and this is where most calculators go wrong. For a chart where the Sun was above the horizon, Fortune is the ascendant plus the Moon minus the Sun; for one where the Sun was below it, the Sun and Moon swap places. Hellenistic sources are unanimous that the reversal applies, but a good deal of twentieth-century software used the day formula around the clock, which is why two calculators frequently disagree about a night chart by a wide margin. This tool applies the reversal and tells you which sect it used and why.

Deciding the sect is itself worth doing properly. The common shortcut is to check which house the Sun falls in, which is wrong for anyone born within a few degrees of sunrise or sunset - exactly the births where the answer matters most. This calculator computes the Sun's actual altitude above the horizon from the sidereal time and your latitude, so the sect is decided by whether the Sun was really up. That needs an exact birth time and place, as does the ascendant the whole formula rests on, so both are required here. The tool also reports the Part of Spirit, Fortune's mirror across the ascendant and the second of the classical pair.