How we check our accuracy.

In our tests (October 2026), the same code that runs on this website gave Lagna (What does Lagna (Ascendant / rising sign) mean?) and planet positions within 1 arc-minute of the Swiss Ephemeris (an independent astronomical library) for all 22 test births, the same Guna Milan (What does Ashtakoota (Guna Milan) mean?) total as AstroSage for all 7 test couples, and Panchang (What does Panchang (the five limbs) mean?) clock times such as sunrise and Rahu Kaal within 1 minute of Drik Panchang in 5 cities. We check calculations — the astronomy, dates and scores — not predictions.

What we checked

Dates are when the reference values were recorded or the comparison was run. AstroSage values were entered by hand on astrosage.com; Drik Panchang and NASA values were copied from their published pages; Swiss Ephemeris values were computed with pyswisseph 2.10.03. The test births include people born in India, the UK, the USA and Australia, and edge cases chosen because a planet or the Lagna sits close to a sign boundary.

What “within 1 arc-minute” means

A zodiac sign is 30 degrees wide and a degree has 60 arc-minutes, so 1 arc-minute is 1/1,800 of a sign. The largest gap we found was 32 arc-seconds (about half an arc-minute). At that size the sign, Nakshatra (What does Nakshatra (birth star) mean?) and pada (What does Pada (quarter) mean?) come out the same unless a planet sits right on a boundary — which is why we include boundary cases in the tests.

Our conventions

Astrology sites can differ simply because they follow different conventions. These are ours:

• Ayanamsa (What does Sidereal (Lahiri ayanamsa) mean?): Lahiri, in the form Drik Panchang uses (the mean Lahiri value, calibrated so planet ingress moments line up with Drik’s published times).
• Rahu (What does Rahu mean?) and Ketu: mean node — the smoothed average position, with Ketu exactly opposite Rahu. Sites that use the “true node” can show Rahu a little earlier or later.
• Houses: whole sign — each house is one full sign counted from the Lagna.
• Vimshottari Dasha (What does Vimshottari Dasha mean?) per the classical text (Brihat Parashara Hora Shastra), with a year of 365.25 days.
• Divisional charts (What does Shodashvarga (the 16 divisional charts) mean?): Parashari rules from Brihat Parashara Hora Shastra, chapter 6, for all 16 charts from D1 to D60.
• Kundali matching: AstroSage’s convention — the same Ashtakoota tables, including which way round the boy and girl are counted.
• Manglik (What does Manglik (Mangal / Kuja Dosha) mean?): AstroSage’s convention — Mars in house 1, 4, 7, 8 or 12 counted from the Lagna and, separately, from the Moon. Both = High, one = Low, none = not Manglik. Classical cancellations are not applied to the level.
• Kaal Sarp (What does Kaal Sarp Dosha mean?): full pattern only — all seven planets from the Sun to Saturn between Rahu and Ketu on one side.
• Panchang: the five limbs are read at local sunrise. Festival and Ekadashi (What does Ekadashi mean?) dates are compared with Drik Panchang’s New Delhi calendar (its Smarta date where it lists two).

Honest limits

• Birth time matters. The Lagna moves about one degree every four minutes, so a birth time that is a few minutes off can change the Lagna, the houses and the finer divisional charts (D27 and above, especially D60). The calculation can only be as exact as the birth time you enter. The divisional-charts section notes when a chart would change within five minutes either side of your time.
• Tithi (What does Tithi (lunar day) mean?) and Nakshatra end times can differ by up to about 2 minutes from another Panchang. They depend only on the Moon, and small differences between astronomical methods shift them by seconds, which can tip the rounding to the next minute. Sunrise, sunset and windows such as Rahu Kaal were within 1 minute in our tests.
• Date-only Moon sign. When only a birth date is known (as on our celebrity pages), the Moon may change sign during that day. On those days we show both signs and say it depends on the birth time.
• Dasha (What does Dasha (planetary period) mean?) dates move with the Moon. A tiny difference in the Moon’s position shifts Dasha start dates by hours. In our tests the current Antardasha start was within 8 hours of the Swiss Ephemeris date for every test birth. A site using a different year length or ayanamsa will show different dates.
• Very old dates. For a few births before 1210 CE, the Moon position differed from the Swiss Ephemeris by up to about 9 arc-minutes (the sign was still the same). Ancient birth dates are often uncertain anyway.
• Tests cover samples, not every possible chart. The table says exactly how many cases were checked. If you find a difference, please tell us at hello@bornclock.com with the birth details and the site you compared with.

How we keep it true

The reference values are stored with the code, and the checks are automatic:

• Weekly drift check. Every Monday at about 03:00 India time, an automatic job sends the 20 reference births and 7 couples both to the current code and to the live bornclock.com website, and compares every answer with the stored reference values. Any difference opens an alert for us to fix.
• Before every release. The same reference tests — Kundali, matching, Panchang, festivals, eclipses and divisional charts — run before each new version of the website goes live, and any failure stops the release. They include a test that re-checks the numbers on this page.
• Dated wording. When we re-run a comparison, we update the date and numbers here.

Questions

Try it yourself: Free Kundali · Kundali Matching · Today’s Panchang · How BornClock works