Calculation Methodology

This page documents how our engine turns two sets of birth details into a Guna Milan result. We publish it so that anyone — a family member, an astrologer or a developer — can check our choices, compare them with their own tradition, and understand why another website might show a different number.

1. Conventions

Every result stores the engine version and the tradition profile, so a saved report can always be traced back to the exact rules that produced it.

2. Astronomy

Ephemeris

Planetary positions come from astronomy-engine, an open-source library (MIT licence) that implements the VSOP87 planetary theory and NOVAS-style corrections. We calculate geocentric apparent positions (as seen from the Earth's centre, including aberration and nutation) for the Moon, Mars, Mercury, Jupiter and Venus, and the Lagna (ascendant) for the place of birth.

Ayanamsa

Tropical longitudes are converted to sidereal ones by subtracting the true Lahiri (Chitrapaksha) ayanamsa — the mean Lahiri value plus nutation, following the Swiss Ephemeris definition. Our unit tests check it against Swiss Ephemeris reference values, and it agrees within 2″ (arc-seconds):

Accuracy budget

The Moon moves about 0.55″ per second of time. An error of 1′ (one arc-minute) in the Moon's position therefore corresponds to roughly 110 seconds of birth time — far smaller than the uncertainty of most recorded birth times. Even so, if the Moon or Lagna lies within 2′ of a boundary (of a nakshatra, pada or sign), the result carries a "near boundary" warning, even for an exact birth time.

Derived values

From the Moon's sidereal longitude we derive the rashi (12 signs of 30°), the nakshatra (27 of 13°20′) and the pada (4 quarters of 3°20′ in each nakshatra). Each nakshatra's gana, yoni (animal and gender) and nadi come from fixed tables; varna, vashya and the rashi lord come from the Moon sign.

3. Time zones and historical time

Birth time is local civil time. We convert it to UTC using the IANA time zone database (through the Luxon library), which records historical changes of offset, including India's local times before Indian Standard Time was fully adopted in the 1950s and war-time adjustments. Daylight-saving rules elsewhere in the world are handled the same way.

Some old Indian records use local times the database does not model precisely, such as Bombay Time (UTC+04:51) or Calcutta Time. For these cases the form accepts an optional fixed UTC offset override (for example +04:51). When an override is used, it is shown on the report.

4. The eight kootas (Ashtakoota, maximum 36)

All eight kootas are based on the Moon of each person. Each has its own guide page with full tables.

5. Doshas and exceptions

Bhakoot dosha and Nadi dosha are the zero-score cases above. Their traditional exceptions are checked as named rules: BHK-C1 (same rashi lord), BHK-C2 (rashi lords mutual natural friends), NAD-C1 (same rashi, different nakshatra), NAD-C2 (same nakshatra, different rashi) and NAD-C3 (same nakshatra, different pada — off by default, configurable).

Manglik dosha: Mars in houses 1, 4, 7, 8 or 12 (the 2nd house is an optional toggle), counted whole-sign from the Lagna and from the Moon. The chart is Manglik if either check is triggered, and "strong" when both are. The same check from Venus is shown as supporting information only. Exceptions MNG-C1 (both partners Manglik), MNG-C2 (Mars in Aries, Scorpio or Capricorn), MNG-C3 (Jupiter conjunct Mars or aspecting it by the 5th, 7th or 9th whole-sign aspect) and MNG-C4 (Mars in the same sign as Mercury, Venus or Jupiter). Age-based cancellation is not applied.

An exception never changes the 36-point total; it is shown as "traditional exception applies" next to the score. Each rule is reported as applies, does not apply or not computable. Full explanations are on the dosha cancellation page.

6. Score bands

These are labels from tradition, not predictions. The report never shows a band on its own: it always shows the kootas where points were lost and any exceptions that apply, and it never states that a marriage will succeed or fail.

7. Birth-time uncertainty

You tell us how accurate each birth time is.

• Exact: one calculation, plus the near-boundary check described above.
• Approximate (±5 to ±180 minutes): the engine examines the whole window. It finds every moment inside it where the Moon crosses a nakshatra, pada or sign boundary, or the Lagna changes sign (located by bisection to within 1 second). It then recalculates every koota and dosha for each sub-interval. Each item is marked stable (same everywhere in the window) or may change (with each possible value and the time range in which it applies).
• Unknown: the engine scans the whole day, 00:00 to 23:59:59 local time. Lagna-based items (such as Manglik from Lagna) are not computable. Moon-based items are stable only if the Moon stays in the same nakshatra pada and sign all day. We never silently assume noon or any other time.

We do not show probabilities or percentages for these cases. A percentage would suggest a precision that the birth record does not support.

8. Name-based matching

When birth details are not available, the first syllable of each name is mapped to a nakshatra pada using the traditional Avakahada Chakra table, and the kootas are calculated from that. Such results are always labelled low confidence, because a name is chosen by people, not determined by the sky. Manglik dosha cannot be computed from a name.

9. Numerology (a separate system)

Numerology is not part of Vedic Guna Milan and never affects the 36-point score. It is shown in its own clearly labelled section.

• Mulank: the digit sum of the day of birth, reduced to 1–9.
• Bhagyank: the digit sum of the full date of birth, reduced to 1–9.
• Planet association: 1 Sun, 2 Moon, 3 Jupiter, 4 Rahu, 5 Mercury, 6 Venus, 7 Ketu, 8 Saturn, 9 Mars. Whether two numbers are friendly, neutral or challenging is derived from the natural friendship of their planets, and the table is shown on the page.
• Lo Shu grid: the digits of the date of birth (zeros ignored) plus the Mulank and Bhagyank are placed on the 3×3 grid (4-9-2 / 3-5-7 / 8-1-6). We show present and missing numbers for each person and the numbers one partner has that the other lacks.
• Name number: Chaldean letter values by default, with a Pythagorean option. Names in Devanagari are first written in Latin letters, and you confirm the spelling.

We do not produce a numerology "compatibility percentage".

10. The AI explainer

The optional AI explainer answers questions about a report in plain language. It never calculates or changes any score, dosha or exception — all numbers come from the deterministic engine described above. It receives only structured report results, not names, dates, times or places of birth.

11. Versioning and verification

The current engine version is shown above this page's content. Every stored result includes the engine version and profile, so changes to rules never silently alter old reports.

Where we are today:

• Done: unit tests for the reference tables, for each koota and cancellation rule (applies / does not apply) and for score bands; ayanamsa tested within 2″ of Swiss Ephemeris reference values; tests for birth-time windows that cross a nakshatra boundary, historical war-time offsets and the Bombay Time override.
• Pending: golden-case verification of complete matches against Swiss Ephemeris; cross-checks against several public calculators, with every disagreement documented together with the rule that causes it; review of all rules and remedy content by a qualified Jyotish practitioner.

12. Known areas where traditions and software disagree

If another website shows a different score for the same pair, one of these is the most likely reason:

• Ayanamsa: Lahiri is the most widely used in India, but some software uses KP, Raman or others. The difference ranges from a few arc-minutes to more than a degree, which can move the Moon into a different nakshatra or pada when it is near a boundary.
• Varna: some traditions assign varna by nakshatra instead of Moon sign.
• Vashya: several slightly different group tables and point grids are in use, including how Dhanu and Makara are split.
• Tara: some count in one direction only, or score it differently.
• Yoni: published 14×14 tables differ in a few cells.
• Gana: Deva–Rakshasa is scored 0 by some and 1 by others (our default is 1).
• Bhakoot and Nadi exceptions: sources accept different sets of exceptions; some software applies none, others apply several disputed ones.
• Manglik: whether the 2nd house is included, whether Venus is a deciding reference, which cancellations are accepted, and whether an age rule is used.
• Birth time handling: some software silently assumes noon or sunrise when the time is unknown; we do not.
• Regional systems: South Indian matching (porutham) is a different system with different factors. We do not cover it in this version.

13. Limitations

• Results are only as reliable as the birth details entered. Place, date and especially time matter.
• Rules follow one well-documented North Indian profile; your family's tradition may differ.
• The engine is new (version 0.1.0) and still awaiting the external verification and practitioner review described above.
• Guna Milan is a traditional practice. Our results are not a prediction of marriage success or failure, and not medical, legal or financial advice.

Questions or a suspected calculation error? Please contact us — we take reported discrepancies seriously and will document what we find.