Ayanamsa is the correction factor that converts tropical zodiac positions to sidereal (Vedic) positions.
There are multiple ayanamsa systems, and our API supports 12 of them: Lahiri, Krishnamurti (KP), Raman, Yukteshwar, True Citra, JN Bhasin, Ushashashi, True Revati, True Pushya, SS Citra, Suryasiddhanta, and Fagan-Bradley.
Each calculates the correction slightly differently.
Lahiri ayanamsa is the official standard adopted by the Indian government and used by 90%+ of Vedic astrologers.
It calculates the gap between tropical and sidereal as approximately 24 degrees currently (exact value changes yearly due to precession).
When generating a Kundli, you take the Sun's tropical position (say 15 degrees Aries) and subtract Lahiri ayanamsa (24 degrees) to get sidereal position (21 degrees Pisces).
Our API uses Lahiri by default but also supports all 12 major ayanamsa systems.
For apps targeting Indian users, ALWAYS use Lahiri unless users specifically request different systems.
KP astrologers prefer Krishnamurti ayanamsa.
Fun fact: the ayanamsa increases about 50 arc-seconds per year, so calculations need to account for the exact birth date.
Swiss Ephemeris (which we use) handles this automatically with NASA JPL precision.
Lahiri ayanamsa is used by 90% of Indian astrologers - the industry standard