Reference
Houses in Astrology
The twelve life areas of the chart, the Placidus system, and how NatalChart.AI calculates and reads them with chart-grounded AI.
The twelve houses
| House | Name | Life domain |
|---|---|---|
| 1st | House of Self | Identity, body, presence, the way you arrive in a room |
| 2nd | House of Resources | Money, possessions, values, what you build with |
| 3rd | House of Mind | Communication, siblings, immediate environment, learning |
| 4th | House of Roots | Home, family of origin, ancestry, inner foundation |
| 5th | House of Heart | Romance, creativity, play, children, self-expression |
| 6th | House of Body | Daily work, health, routine, service, the body's rhythm |
| 7th | House of Partners | Marriage, partnership, contracts, the mirror in the other |
| 8th | House of Depth | Intimacy, shared resources, transformation, the underworld |
| 9th | House of Meaning | Travel, philosophy, higher learning, belief, broad horizons |
| 10th | House of Vocation | Career, public role, authority, what you're known for |
| 11th | House of Community | Friends, networks, futures, collective belonging |
| 12th | House of the Hidden | Solitude, dreams, the unconscious, what's behind the curtain |
The Placidus system
Placidus is a quadrant-based house system: it splits the time-arc the Sun travels between the horizon and the meridian into three equal parts, in both day and night arcs. This produces twelve unequal houses that respect the rising point (Ascendant) and the culminating point (Midheaven) as cusps of the 1st and 10th respectively.
Placidus is the default in NatalChart.AI because it’s the most widely used system in modern western astrology and matches the convention of professional software (astro.com, TimePassages and others).
The four angles
- Ascendant (1st House cusp) — the zodiac degree rising on the eastern horizon at your birth moment. Marks how you arrive.
- IC (4th House cusp) — the lowest point of the chart, opposite the Midheaven. Inner foundation, home of origin.
- Descendant (7th House cusp) — opposite the Ascendant. The mirror in the other.
- Midheaven / MC (10th House cusp) — the highest point of the chart at birth. Public role, vocation.
How NatalChart.AI computes house cusps
- Your birth UTC moment is converted to local sidereal time at the birthplace latitude / longitude.
- The local sidereal time and latitude feed the Placidus algorithm, which returns the twelve cusps.
- Planets are assigned to houses by checking which cusp pair their longitude falls between.
- Aspects to angles (Ascendant, MC) are computed alongside regular planet-to-planet aspects.
Why birth time matters so much for houses
House cusps move about one degree every four minutes. Even a fifteen-minute uncertainty in birth time can shift the Ascendant by 4° and move planets between houses. The reading marks all house-dependent factors as time-sensitive when the birth time is imprecise.
Frequently asked questions
What are the twelve houses?
The houses are twelve sectors of the chart that map to twelve life areas — self, resources, mind, roots, heart, body, partners, depth, meaning, vocation, community, the hidden. They divide the local sky around your birthplace into twelve unequal regions.
What is the Placidus system?
Placidus is the most widely used house system in modern western astrology. It divides time-arcs of the sun's path between the horizon and meridian into thirds, producing twelve unequal houses that respect both the rising and culminating points. NatalChart.AI uses Placidus by default; the engine can compute other systems on request.
How accurate are the houses if I don't know my exact birth time?
House cusps shift about one degree every four minutes, so they're sensitive to birth-time precision. Without an exact time, NatalChart.AI flags house-dependent factors as time-sensitive and downweights them in the reading. See Unknown Birth Time Natal Chart.
Why do houses matter as much as signs?
A planet's sign describes how it expresses; the house describes where in life it expresses. Mars in Aries says 'forceful, direct'; Mars in Aries in the 6th House says 'forceful and direct in daily work and routines'. The house grounds the placement in real life context.