Keep the birth instant fixed
The first rule of a useful comparison is to calculate one natal sky. A birth date and local time are converted to a UTC instant with the historical clock offset entered by the reader. Latitude and longitude determine the local horizon and meridian. The calculator then asks the same astronomical engine for all eight house choices. It checks that every planetary longitude remains identical across them. A different planet degree would indicate a changed ephemeris or birth instant, not a house-system choice.
The comparison shows Sun through Pluto, the Ascendant and Midheaven that locate the chart, twelve cusp degrees for each system, and a matrix of each planet's house number. A highlighted row means at least two methods place that planet in different houses. This is most informative for a point near a cusp. The printed degree gives a reader a way to inspect how close it sits to each border. A changed house does not say which interpretation is true; it identifies the choice that should be named when reading the chart.
Eight methods, three different starting ideas
| Method | What the first or intermediate cusps use |
|---|---|
| Whole Sign | The rising sign's 0° boundary begins house one; each full zodiac sign is a house. |
| Equal House | The Ascendant's exact degree begins house one; every next cusp is 30° farther around the zodiac. |
| Porphyry | The four ecliptic quadrants between Ascendant, Descendant, Midheaven, and IC are each trisected by zodiacal degree. |
| Placidus and Koch | Time-oriented divisions of celestial motion; their cusp methods and high-latitude limits differ. |
| Campanus and Regiomontanus | Spatial divisions projected to the ecliptic through different great-circle constructions. |
| Morinus | Equal divisions of the celestial equator projected to ecliptic cusps; house one need not begin at the Ascendant. |
This website uses its own calculation code and tables. Its Placidus, Campanus, Regiomontanus, Koch, and Morinus implementations have separate source and numerical fixture records linked from the extended natal chart.
Read the angles separately
Whole Sign and Equal House can place the Midheaven inside the ninth, tenth, or eleventh house rather than at the tenth cusp. Morinus can put both the Ascendant and Midheaven inside houses instead of on cusps. A familiar angle therefore retains its actual zodiacal longitude even when a house system does not use it as a boundary. The table lists cusp positions, while the separate extended chart draws angles on a wheel. Do not infer an angle's placement from a conventional house number printed elsewhere.
Check high latitude and source time
The local engine returns a Porphyry fallback when Placidus, Campanus, Regiomontanus, or Koch geometry cannot be obtained at a chosen latitude. A column then names the effective Porphyry result instead of silently labeling it with the requested system. Near a geographic pole, the Ascendant and houses may be undefined and the comparison reports an error. Morinus can have valid cusps at high latitude, but all eight columns still need a defined chart for this side-by-side table.
Even at ordinary latitudes, a remembered birth hour or guessed time zone can move the Ascendant and cusps materially. Before treating a one-house difference as meaningful, check the original record, historical UTC offset, coordinates, zodiac, house method, and cusp degree.
Questions readers ask
Which house system is correct?
House systems are different interpretive and geometrical conventions. The calculator displays their results for one sky. Choosing one requires an explicit method and a reason that makes sense for the reading, not a vote by the number of columns agreeing.
Why does a planet's sign stay the same?
Its tropical ecliptic longitude is computed from the fixed UTC instant. House cusps divide that zodiacal circle from a local place. Changing divisions can change the house while leaving the longitude and sign unchanged.
Why do two columns look identical?
Some systems can have similar cusp degrees for a particular time and latitude. Also, one or more requested quadrant methods can fall back to Porphyry. Look at each column's effective-method label and the printed cusp degrees.