How Your Kundali (Birth Chart) is Calculated

The Three Inputs Every Kundali Needs

A kundali — also called janam kundali or Vedic birth chart — is a map of the sky frozen at the exact moment you were born, as seen from the exact place you were born. To compute one, three pieces of information are non-negotiable:

• Date of birth — the calendar date determines Earth's orbital position relative to the Sun and, by extension, the approximate positions of all planets along the ecliptic.
• Exact time of birth — this is the most sensitive input. The ascendant (lagna) shifts by one full rashi roughly every two hours, and the Moon moves about 13.2 degrees per day. A difference of even four minutes changes the lagna degree by approximately one degree, which can alter nakshatra pada boundaries, dasha start dates, and bhava cusps.
• Place of birth — converted to geographic latitude and longitude. Two people born at the same instant in Mumbai (19.08°N, 72.88°E) and Delhi (28.61°N, 77.21°E) will have different lagnas, different house cusps, and different local sidereal times. The birthplace also determines the timezone offset and any daylight-saving correction needed to convert local clock time to Universal Time.

Without an accurate birth time, a kundali generator can still place the slower planets — Saturn, Jupiter, Rahu, Ketu — with reasonable confidence, but the lagna, Moon's precise degree, and the dasha timeline become unreliable. This is why traditional jyotish places enormous emphasis on recording birth time to the minute.

Swiss Ephemeris: The Computational Engine

Behind every serious kundali app and birth chart calculator is an astronomical ephemeris — a dataset and algorithm that computes where each celestial body sits at any given moment in time. The gold standard is the Swiss Ephemeris, developed by Astrodienst AG in Zurich. It is a compressed implementation of NASA's Jet Propulsion Laboratory Development Ephemeris (JPL DE431), covering planetary positions from 13,201 BCE to 17,191 CE.

Swiss Ephemeris computes geocentric ecliptic longitudes with sub-arc-second precision — typically 0.001 arc-seconds for the inner planets and 0.01 arc-seconds for the outer ones. For reference, one arc-second is 1/3600th of a degree. This level of accuracy far exceeds what any manual panchanga or printed ephemeris table can provide, and it matters: a one-arc-minute error in the Moon's longitude can shift a nakshatra boundary and alter the Vimshottari Dasha timeline by several months.

The library handles precession, nutation, aberration, and the equation of time internally. For Vedic astrology specifically, it supports multiple ayanamsha systems — Lahiri (Chitrapaksha), Krishnamurti, Raman, and others — to convert tropical (Western) longitudes into the sidereal frame that Jyotish uses.

Step-by-Step: How the Calculation Works

1. Convert birth time to Universal Time and Julian Day

The first step is converting the local birth time into Universal Time (UT). This requires knowing the timezone of the birthplace and whether daylight saving time was in effect. The UT is then converted to a Julian Day Number (JDN) — a continuous day count used in astronomy since Joseph Scaliger introduced it in 1583. For example, midnight UT on January 1, 2000 corresponds to JDN 2,451,544.5. The Julian Day provides a single, unambiguous numerical timestamp that the ephemeris engine uses for all subsequent lookups.

2. Calculate planetary longitudes in the sidereal zodiac

Using the Julian Day as input, Swiss Ephemeris computes the geocentric ecliptic longitude of each graha: Surya (Sun), Chandra (Moon), Mangal (Mars), Budha (Mercury), Guru (Jupiter), Shukra (Venus), Shani (Saturn), Rahu (North Node), and Ketu (South Node). These longitudes are initially in the tropical frame. The chosen ayanamsha — most commonly Lahiri, which was approximately 24.17 degrees in 2025 — is subtracted to obtain sidereal longitudes. Each sidereal longitude directly tells you which of the twelve rashis (Mesha through Meena) the planet occupies and at what degree within that rashi.

3. Determine the lagna (ascendant)

The lagna is the zodiac degree rising on the eastern horizon at the moment of birth. Its calculation requires the Local Sidereal Time (LST), which depends on the UT, the observer's geographic longitude, and the Earth's current sidereal rotation angle. The formula converts LST into the oblique ascension, then applies the observer's latitude to find which ecliptic degree intersects the eastern horizon. Because the Earth rotates roughly one degree every four minutes, the lagna sweeps through all 360 degrees in about 24 hours — meaning it changes rashi approximately every two hours. This is precisely why birth time accuracy is so critical.

4. Place planets in houses (bhavas)

In the most common Vedic system — the whole-sign house system — the rashi containing the lagna becomes the first house, the next rashi becomes the second house, and so on. Each planet is placed in the house corresponding to its rashi. Some practitioners use the Sripati or Placidus systems, which calculate unequal house cusps based on the trisection of diurnal and nocturnal semi-arcs, but the whole-sign approach dominates in traditional North Indian and South Indian jyotish.

5. Calculate nakshatra and pada

The 360-degree sidereal zodiac is divided into 27 nakshatras, each spanning exactly 13°20' (13.333 degrees). Each nakshatra is further divided into four padas of 3°20' each. To find the nakshatra, divide the planet's sidereal longitude by 13.333 — the integer part gives the nakshatra index (0 = Ashwini, 1 = Bharani, ... 26 = Revati), and the fractional remainder, divided by 3.333, gives the pada (1 through 4). The Moon's nakshatra at birth (Janma Nakshatra) is particularly important — it determines the starting point of the Vimshottari Dasha system and is used in compatibility matching (Milan).

6. Compute the Vimshottari Dasha timeline

The Vimshottari Dasha system allocates a 120-year cycle across nine planetary lords in a fixed sequence: Ketu (7 years), Shukra (20), Surya (6), Chandra (10), Mangal (7), Rahu (18), Guru (16), Shani (19), Budha (17). The Moon's exact degree within its birth nakshatra determines how far into the first dasha the native is born. If the Moon is at 60% of a nakshatra ruled by Shukra, then 60% of Shukra's 20-year period has already elapsed at birth, leaving 8 years of Shukra mahadasha remaining. From there, each subsequent mahadasha follows in sequence. Sub-periods (antardasha, pratyantardasha) are calculated by proportionally subdividing each mahadasha among all nine lords in the same order.

North Indian vs South Indian Chart Styles

Once the planetary positions and houses are computed, the data can be displayed in two traditional formats:

North Indian chart (diamond style) — the houses are fixed in position. The first house is always at the top-center diamond, the second house to its upper-right, and so on in a counter-clockwise direction. The rashis rotate: whichever rashi the lagna falls in gets placed in the first house position. This format makes it easy to compare house-level analysis across different charts, since the house positions never move.

South Indian chart (grid style) — the rashis are fixed in position. Mesha (Aries) is always in the second cell of the top row, Vrishabha (Taurus) to its right, and so on in a clockwise direction. The lagna is marked with a diagonal line or the word "Asc" in the cell of its rashi. This format makes it easier to track planetary transits, since each rashi always occupies the same box.

Both formats encode identical astronomical data. The choice is largely regional — North Indian families tend to prefer the diamond layout, while South Indian families use the grid. A good kundali app should support both.

Key Elements of the Completed Chart

Lagna (Ascendant) — the most personal point in the chart. It determines the first house and sets the framework for all twelve houses. Your lagna rashi shapes your outward personality, physical constitution, and how others perceive you. Its degree determines which nakshatra pada governs the ascendant, adding another layer of specificity.

Chandra Rashi (Moon Sign) — the rashi occupied by the Moon. In Vedic astrology, the Moon sign carries more weight than the Sun sign. Daily rashifal (horoscope) is based on the Chandra Rashi. It governs the mind, emotions, instinctive reactions, and overall mental temperament.

Surya Rashi (Sun Sign) — the rashi occupied by the Sun. It represents the soul, authority, vitality, and the father. Note that the Vedic Sun sign (sidereal) differs from the Western Sun sign (tropical) by about 23-24 days due to the ayanamsha offset.

Janma Nakshatra — the Moon's nakshatra at birth. There are 27 nakshatras, each with a distinct ruling deity, planetary lord, and symbolic meaning. The nakshatra further divides into four padas, each mapped to a specific navamsha rashi. Your nakshatra determines your Vimshottari Dasha starting point, the first syllable of your Vedic name, and plays a central role in Ashtakoot Milan (compatibility matching).

Manglik Dosha: How It's Determined

Manglik dosha (Kuja dosha) is one of the most widely checked conditions in Vedic astrology, especially for marriage compatibility. The rule: if Mars (Mangal) is placed in the 1st, 2nd, 4th, 7th, 8th, or 12th house from the lagna, the native is considered Manglik. Some traditions also check from the Moon and Venus, creating a more nuanced three-point assessment.

The logic is straightforward once the kundali is computed: determine which house Mars occupies, and check if that house number is in the set {1, 2, 4, 7, 8, 12}. If yes, manglik dosha is present. However, classical texts describe several cancellation conditions (dosha bhanga): Mars in its own sign (Mesha or Vrishchika), Mars in conjunction with or aspected by Jupiter, Mars in the 2nd house in Mithuna or Kanya, and others. A thorough kundali generator evaluates both the presence and the cancellation conditions.

It is estimated that roughly 40-50% of people have some form of Manglik dosha by the basic house rule alone, which is why the cancellation conditions matter — they significantly reduce the effective percentage of charts where the dosha is considered active and relevant.

How Nithya Automates All of This

Manually computing a kundali requires looking up ephemeris tables, performing sidereal time calculations, interpolating planetary positions, and then drawing the chart by hand. A trained jyotishi might spend 30 minutes on a single chart. Nithya collapses this to seconds.

When you enter your birth date, time, and place in the Nithya app, the backend geocodes your birthplace to latitude and longitude, converts your local time to a Julian Day, and feeds it into Swiss Ephemeris. In a single pass, it computes all nine planetary longitudes in the Lahiri sidereal frame, determines the lagna, places planets in whole-sign houses, identifies each planet's nakshatra and pada, calculates the complete Vimshottari Dasha timeline down to the pratyantardasha level, and evaluates Manglik dosha with cancellation checks.

The result is a complete janam kundali — lagna chart, Moon chart, navamsha chart, nakshatra details, dasha timeline, and dosha analysis — generated instantly and displayed in a clean, readable format. No manual tables, no guesswork, no cost. Just accurate Vedic astronomy, computed to sub-arc-second precision, delivered to your phone.