Free Derivative Houses Calculator

A derivative house is the house in your natal chart that represents a derived topic (your spouse's career, your sibling's children, your mother's father) instead of a primary one. You pick a base house, treat it as the alternate first house, count counterclockwise to the topical position you want, and the house you land on is the derived house in your own chart. The technique appears in early Hellenistic sources and shows up most heavily in horary practice, with natal applications growing more popular in the last few decades.

Some practitioners also call this "turning the chart" or "turning the wheel." The math is the same either way: any house can be promoted to a temporary first, and the rest of the chart re-reads from that new starting point.

Turning the chart means treating any house in your natal chart as a temporary first house, then reading the other eleven from that new starting point. Whatever house you land on at the position you want is the derived house for your topic. The five-step process:

1. Pick the base house. The house that rules the person or topic you are starting from. Spouse is the seventh. Sibling is the third. Mother is the tenth in older Western practice and the fourth in some modern variants.
2. Treat that house as the new first. Imagine the chart turned so your base house sits at the ascendant.
3. Count counterclockwise to the topical house. Career is ten houses around. Children, five. Health, six.
4. Read the house you land on. That is your derived house, the one in your own chart that carries the texture of the derived topic.
5. Look at the sign on its cusp and the planet that rules that sign. The ruler's natal placement gives you the interpretive depth.

If you would rather skip the counting, the math is plain: add the base house and the topical house, subtract two, take the result modulo twelve, and add one. In code form: derived = ((base + topic − 2) mod 12) + 1. The seventh from the seventh comes out to the first, your partner's partner, which is you.

These are the questions people actually bring to the technique. Each subsection links to its anchor so you can share a direct reading.

The matrix below shows every base-house and topical-house pairing. Pick the row for your base house (the topic you are starting from), find the column for the topical house (the matter you want to know about that topic), and read the cell value. That is the house in your own chart where the derived topic lives.

The diagonal is worth a second look on its own. The seventh from the seventh, the fifth from the fifth, the ninth from the ninth: each one folds back through the wheel and lands at a meaningful midpoint, which is why those particular derivations show up so often in practical work.

Horary leans on derivation harder than natal does, and there is a reason. A horary chart is cast for a single question and a single querent, which means the third party in the question (the lost dog, the sibling's spouse, the absent parent, the missing object) needs a clean, repeatable assignment in the chart. Derivation gives you that assignment without ambiguity, because horary asks one question at a time and the chain almost never goes more than two hops deep.

In natal practice, derivation works best when the people in your life are clearly singular: one mother, one sibling, one current partner. As soon as you are trying to derive a chart-house for "my second sibling's third partner," you are stacking enough assumptions that the reading stops being predictive and turns into description after the fact. Most working astrologers treat one-hop derivations (spouse's career, sibling's spouse) as solid, two-hop derivations as suggestive in clean cases, and three-hop as essentially decorative.

Western astrology has been arguing about the parental houses for a long time, and the disagreement is not going to resolve. Hellenistic and a substantial branch of modern practice put the father at the fourth and the mother at the tenth. A different modern convention, popularized in the twentieth century, flips them: mother at the fourth, father at the tenth, often with the rationale that the fourth is the inner home and the tenth is the public-facing parent.

The calculator above defaults to the older convention and lets you switch. Pick whichever your school of practice already uses for mother, then apply it consistently across every parental derivation in this chart. The grandparent positions, the aunts and uncles, the parental careers and finances, all of them flow from the parent assignment. Mixing the two conventions inside one reading turns the math into nonsense.

Once you have the derived house, the next move is the natal ruler. Look at the sign on that house's cusp, then look up which planet rules that sign in your chart, then check that planet's natal position, dignity, and aspects. The derived house tells you which area of life carries the topic; the ruler tells you how it is actually expressing.

For a quick view of every house's ruler at once, pair this calculator with the Lord of the Houses Calculator. It surfaces all twelve rulers and their conditions in a single view, which you can then turn into derived readings without manually chasing each cusp.

The technique has real limits, and naming them up front is what separates a working reading from wishful thinking.

Multiple siblings is the common one. If your sister has three brothers, the third house technically refers to "the eldest younger sibling, then count counterclockwise" or "the eldest sibling, then count clockwise" depending on whose tradition you are following, and either way the chain past the first sibling is approximate. Same problem with multiple spouses: the seventh is the first marriage, the ninth is the second, the eleventh is the third, and you are already drifting from convention by the time you are on the third.

Adoptive vs biological is another snag. Some practitioners use the natural-parent house for biological lineage and the step-parent or adopting-parent house for the actual day-to-day raiser; others give priority to whoever raised you regardless of biology. Both are defensible, and both produce different readings. Pick a rule and apply it consistently.

Three-hop chains (your sibling's spouse's career, your child's friend's parent) work mathematically but tend toward decoration in practice. The signal is real on the first hop, suggestive on the second, and barely audible on the third. Use them as confirmation, not as primary read.