Part of Fortune calculator: your sign and house

The Part of Fortune, or Lot of Fortune, is one of the lots of Hellenistic astrology: a point calculated from three positions instead of seen in the sky. In the ancient texts it stood for the body, well-being and material fortune, and it was weighed almost as heavily as the Moon. It marks the place where the Sun, the Moon and the ascendant meet in a single number.

In a modern chart it is a minor point, read as a part of life where things tend to go smoothly: the area, set by its house, where you feel at ease and where effort seems to pay. It is a tradition to think with, not a promise of luck.

By day the Part of Fortune is the Ascendant plus the Moon minus the Sun; by night it is the Ascendant plus the Sun minus the Moon. A day chart is one where the Sun was above the horizon at birth, in the 7th to 12th house, and a night chart one where it was below. The two formulas mirror each other: the point lies as far from the Ascendant as the Moon lies from the Sun, forward by day and backward by night.

Some modern astrologers use the day formula for every chart. The calculator follows the traditional rule and tells you which one it applied. If your Sun was close to the horizon, a few minutes in your birth time can change the formula and move the point to a different sign.

The sign of the Part of Fortune is read as the style in which ease and well-being tend to arrive, and the house as the area of life where they show. A point in the 10th house is read as luck in public life, one in the 5th as luck in creative work and play, one in the 11th as luck through friends and groups.

Planets close to the point, within a few degrees, color it: Jupiter and Venus are traditionally read as supportive, Saturn and Mars as demanding. As always in astrology, these readings are a lens for reflection, not a prediction.

The planet ruling the sign of the Part of Fortune is called its ruler, and astrologers look at where it stands: its sign and house show how the fortune of the point is put to use. If your point is in Cancer, its ruler is the Moon; in Sagittarius, Jupiter. Traditional astrology uses the seven visible planets only, so Scorpio is ruled by Mars, Aquarius by Saturn and Pisces by Jupiter, while modern astrology adds Pluto, Uranus and Neptune.

The calculator shows both rulers when they differ, each with its sign, degree and house. Read the traditional ruler as the older layer and the modern one as an addition.

The Part of Fortune itself does not depend on the house system, only the house it is placed in does. Placidus and Koch divide the sky by time, equal houses give every house 30 degrees from the Ascendant and whole sign houses make each sign one house. A point near a cusp can change house when you switch, and the calculator lets you try all four.

The day or night test does not depend on the system either: it asks whether the Sun is above the horizon, between the Descendant and the Ascendant going forward. Near the polar circles Placidus and Koch cannot be drawn, so equal houses stand in and the tool says so.

The Part of Fortune is built on the Ascendant, which travels once around the zodiac every 24 hours and changes sign about every two hours. Two people born on the same day in the same city can have the point in different signs, and a birth date alone says nothing about it. That is why the calculator does not guess at noon: without a time it shows nothing house-based.

A birth certificate or hospital record is the best source for the time, then a parent's memory of the hour. A few minutes of error rarely matters, but close to a sign change, or when the Sun is near the horizon, ten or fifteen minutes can. The rising sign calculator needs the same time.

The calculator works out the sidereal time at your birthplace, the Ascendant with the standard formula, and the apparent positions of the Sun and Moon from the VSOP87 theory and Meeus's lunar series. It then applies the day or night formula and places the result by sign, degree and house. We check the Ascendant, Sun and Moon against the Swiss Ephemeris, and the point agrees to within a fraction of an arcminute.

Everything is computed in your browser, and the tool is free. To see the Part of Fortune among all your planets and aspects, open the birth chart calculator; for the angle it hangs from, try the midheaven calculator.