Seven parts and two starting signs
Saptamsha (D7) divides a sidereal rāśi into seven equal parts. Each part is exactly 30°/7, about 4°17′08.57″. In an odd sign (Aries, Gemini, Leo, Libra, Sagittarius, Aquarius), part one maps to that same sign. In an even sign (Taurus, Cancer, Virgo, Scorpio, Capricorn, Pisces), part one maps to the seventh sign counted inclusively from it. Each later part advances one zodiac sign.
This distinction matters. At 10° Gemini, a point is in part three and maps to Leo. At 19° Virgo, a point is in part five; the sequence starts from Pisces and reaches Cancer. These are the published examples in P. V. R. Narasimha Rao's Vedic Astrology: An Integrated Approach, §6.2.7.
The tool calculates sidereal D1 positions with Astronomy Engine 2.1.19 and an approximate Lahiri ayanamsha, then applies the D7 sign rule. It includes seven classical grahas and mean Rahu and Ketu. A timed D1 ascendant supplies the D7 Lagna; the calculator asks for the historical UTC offset and does not infer it from a place name.
What the chart displays
Each result row retains the original D1 sidereal sign and degree, identifies the numbered seventh, states whether the count began in the D1 sign or its seventh, and shows the derived D7 coordinate. The South Indian diagram keeps signs fixed and marks the transformed Lagna.
D7 is traditionally consulted for questions about children and progeny, but a chart alone cannot establish fertility, predict an individual child, or replace a medical or personal decision. Use the D7 method guide to check the arithmetic and source. The D1 rāśi chart shows the positions from which D7 was derived.