One starting degree, twelve equal intervals
For house number n, add 30° times n minus one to the Ascendant’s longitude, then reduce the result to the 0°–360° circle. A cusp at 370° becomes 10°. Keep full precision for placement; rounded display degrees should not decide which side of a boundary a planet occupies.
Equal houses distribute zodiac longitude equally. This does not mean equal time above the horizon, equal projected areas of the sky or equal sizes on every chart drawing.
Why the tenth cusp can differ from the MC
The equal tenth cusp is Ascendant plus 270°, reduced modulo 360°. The astronomical MC comes from the intersection of the meridian and ecliptic. These are different constructions. Keep the MC and its opposite, the IC, visible rather than relabelling the equal tenth and fourth cusps as those axes.
What to hold constant in a comparison
Use the same birth time, location and zodiac when comparing equal houses with whole sign or Placidus. Switching only the house system preserves planetary longitudes, but a moved cusp may change a planet’s house and the symbolic reading attached to it.
A CONCRETE EXAMPLE
Worked arithmetic: an equal tenth cusp is not automatically the MC
At ARMC 100°, latitude 40° N and obliquity 23.4393°, the calculated Ascendant is 187.988849°. Equal cusps are therefore 187.988849°, 217.988849°, 247.988849° and so on.
For house ten: 187.988849° + 270° − 360° = 97.988849°, or Cancer 7.988849°. The independently calculated MC is 99.189513°, or Cancer 9.189513°. Their separation is 1.200664°. This example checks the geometry; it is not a personal birth chart or a predicted life event.
Read it in your own chart.
Keep the date, recorded time, location and zodiac visible as you compare results. Guest calculations need no account.
Create your free chartCommon questions
Do equal houses always start at 0° of a sign?
No. They retain the Ascendant’s degree within the sign. Starting every house at 0° of the successive signs describes whole sign houses.
Are equal houses available at every latitude?
They do not use the Placidus/Koch polar semiarcs, but still require a unique Ascendant. Sky Degrees rejects geographic poles and degenerate geometry rather than fabricating a starting degree.
Calculation & interpretation
New personal calculations use Skyfield with JPL DE440 data and the site’s documented house and zodiac rules. The preserved Greenwich teaching chart has its own historical source label. Worked arithmetic and geometry examples are labelled separately. Astrological meanings are symbolic conventions, not established scientific predictions.
Birth time and place affect angles and houses. Unsupported or ambiguous inputs return an error rather than an invented chart. Personal results stay in browser state and do not create public result URLs.
Read the calculation settings guide