A birth chart splits the local sky into twelve houses. The free chart uses Placidus when a birth time is known. Without a time, houses are omitted — see Unknown birth time.
Systems explained
Placidus
A time-based quadrant system. Default for the free chart. Undefined at some polar latitudes; the chart then uses Porphyry and names that fallback.
Koch
Another time-based quadrant system. Same polar fallback to Porphyry as Placidus when a cusp is undefined.
Porphyry
Trisects the quadrants between the Ascendant and Midheaven. Defined at polar latitudes. Used as the fallback when Placidus or Koch cannot produce cusps.
Equal
Twelve 30° houses starting from the Ascendant. Needs the Ascendant; no polar fallback.
Whole Sign
House 1 is the whole sign that contains the Ascendant; each following sign is the next house. Needs the Ascendant.
Also calculated (22 systems)
The calculator can produce 22 house systems. The free chart uses Placidus. Measured checks are listed on Credits.
- Placidus
- Whole Sign
- Equal
- Koch
- Porphyry
- Regiomontanus
- Campanus
- Alcabitius
- Topocentric
- Morinus
- Meridian
- Equal MC
- Vehlow
- Carter
- Horizon
- Krusinski
- APC
- Sripati
- Pullen SD
- Pullen SR
- Sunshine
- Gauquelin
Polar policy
| System | Polar behaviour |
|---|---|
| Placidus, Koch | Undefined at |lat| ≥ 90° − ε and when a cusp is circumpolar. The chart still draws and falls back to Porphyry, with an explicit warning. |
| Porphyry, Equal, Whole Sign | Defined. Equal / Whole Sign need only the Ascendant. |
| Regiomontanus, Campanus, Topocentric | Defined at polar latitudes. When the MC is below the horizon, house 10 is the above-horizon meridian (IC). |
| Alcabitius | Defined wherever the Ascendant is defined. No Porphyry fallback. |
| Meridian (axial), Morinus | Always defined (independent of latitude). House 1 is not the geographic Ascendant; Meridian house 10 is the MC. |
One birth, two house systems
The same Stockholm sample (1990-04-12 08:30) under Placidus and Whole Sign. Whole Sign house 1 is the whole rising sign.
Placidus
Drag the AC marker to spin the wheel. Arrow keys rotate two degrees; Home resets. Hover or tap an aspect line for its type, orb and a short meaning.
Whole Sign
Drag the AC marker to spin the wheel. Arrow keys rotate two degrees; Home resets. Hover or tap an aspect line for its type, orb and a short meaning.