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The navamsa divides each sign into nine parts of 3 degrees 20 minutes each and rebuilds the chart from where every planet falls. It is the most consulted divisional chart after the birth chart itself, traditionally read for marriage and for the underlying strength of a planet. A planet that looks well placed in the birth chart but poorly placed in the navamsa is generally treated as weaker than it first appears.

Lahiri, also called Chitrapaksha, anchored to 23 degrees 15 minutes 00 seconds on 21 March 1956 following the Indian Calendar Reform Committee definition. This is the standard used by the Indian government and by most Indian software, so results line up with the panchangs and charts you are likely to be comparing against.

Almost always one of three reasons. Different ayanamsa, since Raman and Krishnamurti values differ from Lahiri by several arc minutes. Different house system, since whole-sign, Placidus and Sripati produce different cusps. Or a different timezone assumption for historical dates, which matters a great deal for Indian births before 1955 when local time rules changed. The specification table lists exactly what Amsha uses so you can compare like with like.

The ascendant moves roughly one degree every four minutes, so house positions and the navamsa become unreliable quickly without an accurate time. Planetary positions in the birth chart are far more forgiving, and the Moon only moves about half a degree per hour. If you have a time to the nearest hour, sign positions will usually be right, but treat house-based and divisional readings with caution.

No. The calculators run in your browser using JavaScript on your own device, and the pages they sit on are static files with nothing behind them to send anything to. Your birth details are not logged, stored or transmitted. If you save a chart it is kept in your own browser and stays there. The one feature that does contact a server is the AI assistant, and it is sent figures worked out from your chart rather than your birth date, time or place; the privacy page sets out exactly what it sends.

The classical set is sixteen, called the shodashavarga, running from the birth chart itself through to the D60 shashtiamsa. Parashara describes each one and the area of life it governs. Amsha computes all sixteen, and will also divide a chart by any other number if you want to explore beyond the traditional set.