How we calculate your chart, and how to check it
The positions in your chart are calculated, not generated. The words around them are written by AI. This page shows where the line is, what we test against, and how you can check any number yourself.
What we calculate and what AI writes
Planets, the Moon, lunar nodes, Lilith, Chiron, the Ascendant, the Midheaven, houses and aspects are calculated by our engine from your date, time and place of birth. The language model never chooses a position: it receives the finished chart and writes the interpretation in the tone you pick. If the text ever contradicts the table, the table is right.
Where the numbers come from
Positions come from the Swiss Ephemeris, a planetary ephemeris built on NASA JPL integrations and used by professional astrology software. Your local clock time is converted to universal time with the historical time zone and daylight saving rules of your city on your birth date; before standard time zones existed, we use the local mean time of the birthplace. That conversion is where most online calculators go wrong.
Control checks
These checks run against values we did not calculate ourselves. They live in the project as automated checks and can be rerun at any time.
| What is checked | Reference | Our result |
|---|---|---|
| Midheaven, 1 January 2000, 12:00, Moscow | 2°42′ Capricorn, calculated independently by three other Russian-language calculators | matches within 0.0035° (about 13 arc seconds) |
| Albert Einstein, Ulm, 14 March 1879, 11:30 local mean time (Rodden AA) | Astrotheme: Ascendant 11°38′ Cancer, Midheaven 12°50′ Pisces, Moon 14°32′ Sagittarius | all three within 1′ to 2′ |
| Lahiri ayanamsa on 21 March 1956 (sidereal zodiac) | 23°15′00″, the definition of the Indian Calendar Reform Committee of 1955 | within 1′ |
| Saturn return interval | sidereal period of Saturn, 29.46 years | 29.4 years ± 0.6, all passes of the retrograde loop found |
| Historical clocks: Moscow 1990 summer time, Berlin 2000 winter and summer, Boston 1850 local mean time | official time zone history | universal time matches to the second |
| Seven house systems and polar latitudes | definitions of the systems; above 66° Placidus and Koch are undefined | the Midheaven is identical in all seven systems; above 66° we switch to Porphyry and say so |
Benchmark: can an AI model calculate a chart by itself?
People often ask a chatbot to "calculate my birth chart". We gave a language model 20 made-up births (different years, cities, time zones and times of day) and asked for the sign and degree of the Sun, the Moon and the Ascendant, then compared the answers with our engine.
| Point | Sign correct | Typical error | Largest error |
|---|---|---|---|
| Sun | 20 / 20 | 0.1° | 0.3° |
| Moon | 19 / 20 | 2.8° | 16.7° |
| Ascendant | 15 / 20 | 0.6° | 24.4° |
Model gemini-3.7-flash, no tools or web search, measured 3 October 2026. Results change from model to model and over time, so the date matters.
The slow points are fine: the Sun moves about a degree a day, so a model gets it right. The fast points are where it breaks: the Moon moves about 13° a day and the Ascendant about a degree every four minutes, and 5 of 20 Ascendants landed in the wrong sign. A wrong Ascendant moves every house, so the whole reading built on it is about someone else.
All 20 cases
| Birth | Point | Engine | Model |
|---|---|---|---|
| 1952-07-04 05:20, Moscow, Russia | Sun | Cancer 12.1° | Cancer 12.2° |
| Moon | Scorpio 25.3° | Scorpio 28.3° | |
| Ascendant | Cancer 26.6° | Cancer 26.9° | |
| 1958-11-23 23:40, London, United Kingdom | Sun | Sagittarius 1.2° | Sagittarius 1.4° |
| Moon | Taurus 4.5° | Taurus 11.5° | |
| Ascendant | Virgo 7° | Virgo 7.3° | |
| 1961-02-14 13:05, New York, USA | Sun | Aquarius 25.8° | Aquarius 25.9° |
| Moon | Aquarius 17.6° | Aquarius 18.2° | |
| Ascendant | Cancer 3.3° | Gemini 28.9° | |
| 1964-09-30 07:55, Tokyo, Japan | Sun | Libra 6.8° | Libra 6.9° |
| Moon | Cancer 24.2° | Cancer 18.2° | |
| Ascendant | Scorpio 4.8° | Scorpio 21.7° | |
| 1967-06-18 18:30, Sydney, Australia | Sun | Gemini 26.4° | Gemini 26.6° |
| Moon | Scorpio 4.9° | Scorpio 16.8° | |
| Ascendant | Capricorn 18.9° | Sagittarius 24.5° | |
| 1970-03-21 02:15, Sao Paulo, Brazil | Sun | Aries 0.2° | Aries 0.4° |
| Moon | Virgo 9.4° | Virgo 12.1° | |
| Ascendant | Aquarius 6.5° | Capricorn 24.8° | |
| 1973-12-08 10:45, Mumbai, India | Sun | Sagittarius 16° | Sagittarius 16° |
| Moon | Taurus 20.4° | Taurus 11.1° | |
| Ascendant | Aquarius 9.6° | Capricorn 26.5° | |
| 1976-08-01 16:10, Berlin, Germany | Sun | Leo 9.5° | Leo 9.5° |
| Moon | Libra 22.5° | Libra 21.1° | |
| Ascendant | Sagittarius 10.9° | Sagittarius 11.2° | |
| 1979-04-27 21:25, Paris, France | Sun | Taurus 6.9° | Taurus 7.1° |
| Moon | Taurus 23° | Taurus 21.7° | |
| Ascendant | Scorpio 12.6° | Scorpio 17.5° | |
| 1981-10-15 04:50, Los Angeles, USA | Sun | Libra 22° | Libra 22.2° |
| Moon | Taurus 19.5° | Taurus 18.4° | |
| Ascendant | Virgo 24.3° | Virgo 23.7° | |
| 1984-01-29 12:00, Saint Petersburg, Russia | Sun | Aquarius 8.6° | Aquarius 8.9° |
| Moon | Sagittarius 28.3° | Sagittarius 26.6° | |
| Ascendant | Gemini 8.3° | Gemini 8.9° | |
| 1986-05-09 08:35, Kyiv, Ukraine | Sun | Taurus 18.3° | Taurus 18.3° |
| Moon | Taurus 21.2° | Taurus 11.4° | |
| Ascendant | Gemini 27.8° | Cancer 2.4° | |
| 1988-08-19 19:15, Almaty, Kazakhstan | Sun | Leo 26.7° | Leo 26.8° |
| Moon | Scorpio 13.3° | Scorpio 13.5° | |
| Ascendant | Capricorn 25.5° | Capricorn 26.1° | |
| 1990-05-15 14:30, Mexico City, Mexico | Sun | Taurus 24.7° | Taurus 24.7° |
| Moon | Aquarius 1.6° | Aquarius 11.5° | |
| Ascendant | Virgo 22.1° | Virgo 22.4° | |
| 1992-11-02 06:05, Cairo, Egypt | Sun | Scorpio 10° | Scorpio 10.1° |
| Moon | Aquarius 7.7° | Aquarius 24.3° | |
| Ascendant | Scorpio 8.1° | Scorpio 9.9° | |
| 1995-02-26 22:50, Seoul, South Korea | Sun | Pisces 7.5° | Pisces 7.6° |
| Moon | Aquarius 0.4° | Capricorn 26.4° | |
| Ascendant | Scorpio 2.8° | Scorpio 14.7° | |
| 1998-07-12 11:20, Toronto, Canada | Sun | Cancer 20.1° | Cancer 20.2° |
| Moon | Aquarius 27.7° | Aquarius 26.4° | |
| Ascendant | Virgo 23° | Virgo 23.1° | |
| 2001-09-05 03:40, Madrid, Spain | Sun | Virgo 12.6° | Virgo 12.6° |
| Moon | Aries 6.4° | Aries 6.3° | |
| Ascendant | Cancer 23.2° | Cancer 23.2° | |
| 2004-12-24 15:55, Bangkok, Thailand | Sun | Capricorn 2.9° | Capricorn 3° |
| Moon | Gemini 8.2° | Gemini 5.5° | |
| Ascendant | Gemini 4.9° | Gemini 5.1° | |
| 2008-03-10 09:10, Novosibirsk, Russia | Sun | Pisces 19.9° | Pisces 20.2° |
| Moon | Aries 22.1° | Aries 20.9° | |
| Ascendant | Gemini 3.7° | Gemini 3.7° |
How to check any chart yourself
- Take a birth with a documented time, for example Albert Einstein: Ulm, 14 March 1879, 11:30. Enter it into our rising sign calculator and into any established calculator you trust. The Ascendant should agree to within a few arc minutes.
- Compare degrees, not just signs. Two calculators can agree on the sign and still disagree by several degrees if one of them applied the wrong time zone.
- If two results differ by about 15° on the Ascendant, look at daylight saving first: an hour of clock error is roughly that much.
Where the method stops
- Without a birth time there is no Ascendant and no houses. We show you that instead of guessing a sign.
- If the Moon changed sign on your birth day and the time is unknown, we show both signs and the moment of the change.
- Astrology is not a science and does not predict events. The calculation is exact; the meaning given to it is interpretation, written by AI.
Questions about accuracy
Is the chart calculated by AI?
No. Positions are calculated by our engine on Swiss Ephemeris data. The language model only writes the interpretation of the finished chart.
Why does my Ascendant differ from another website?
Most often because of the time zone: many tools apply today’s offset to an old date. We use the historical rules of your city on your birth date, and local mean time before standard time existed.
How accurate is it?
For points we can test against independent references, the difference is under two arc minutes, usually far less. The real limit is the accuracy of your birth time: four minutes of error move the Ascendant by about a degree.
Can I trust ChatGPT or Gemini to calculate my chart?
For the Sun sign, usually yes. For the Moon and especially the Ascendant, not reliably: in our benchmark 5 of 20 Ascendants were in the wrong sign. If a chatbot interprets your chart, give it positions calculated by a real ephemeris.