The Navamsa (D-9) divides each 30° zodiac sign into 9 parts, then assigns each part a zodiac sign under a stated rule. Each part spans 3°20′. It is derived from the same birth longitudes as the D-1 chart; it is not a second observation of the sky.
The sign-assignment rule
For movable signs begin with the same sign; for fixed signs begin with the ninth sign counted inclusively; for dual signs begin with the fifth. “Ninth from Taurus” means Capricorn, not nine additional signs after Taurus.
For a degree d within a sign, the segment number is floor(d × 9 ÷ 30) + 1, with d at least zero and less than 30. Here “floor” means discard the fractional part. Count the starting sign as one. Keep sign assignment separate from interpreting what a planet means.
Worked example
A planet at 12° Aries lies in the fourth segment: 10°00′ up to, but not including, 13°20′. Start at Aries and count Aries, Taurus, Gemini, Cancer: the D-9 sign is Cancer. At 12° Taurus the starting sign is Capricorn, so the fourth segment gives Aries. The same within-sign degree does not imply the same divisional sign.
These are invented longitudes for teaching the calculation, not a client’s chart or a claimed life outcome. Self-check: 25° Leo gives segment 8, because floor(25 × 9 ÷ 30) + 1 = 8. Leo is fixed, so the start is the ninth sign counted inclusively from Leo, which is Aries; the eighth sign from Aries is Scorpio. If you reach a different sign, check whether you counted the starting sign as zero instead of one.
What it is used for
Navamsa is commonly used in Jyotish discussions of marriage, dharma and planetary dignity. It cannot establish a spouse’s character, fidelity or a marriage outcome. Vargottama means a planet occupies the same sign in D-1 and D-9; it is a repeated calculated classification, not independent confirmation that an event will happen.
Birth-time sensitivity
The divisional ascendant can change when the underlying ascendant crosses a segment boundary, and a D-9 segment is 3°20′ wide. The ascendant moves about one degree every four minutes on average, so that is very roughly thirteen minutes of birth time. The real rate varies with latitude and sign, so treat this as an order of magnitude, not a tolerance. If the birth time is approximate, calculate at both ends of the plausible range and note which placements change.
A reading exercise with boundaries
Compare one planet’s two sign placements, then write which rule led to each. If a relationship question prompted the reading, separate those entries from things only the people involved can answer: expectations, consent and communication. Do not let a Navamsa label substitute for those conversations.
When two tools disagree, compare birth time and time zone, zodiac/ayanamsha, degree precision and the division rule before comparing interpretations. A one-degree difference between two ayanamshas is about 30% of a D-9 segment, enough to move a planet that sits near a boundary into the adjacent Navamsa sign. More decimal places do not repair an uncertain birth record.
Sources and related guides
Calculation reference: Brihat Parashara Hora Shastra, chapter 6, the section describing the sixteen divisions. The cited text documents the traditional scheme; it does not validate personal predictions. Our examples above show the arithmetic without reproducing the text’s promised outcomes. For context read what divisional charts are and how to compare them.