Calculation tool and methodology
Birth Chart Calculator
Calculate your Sun, Moon, Rising sign, Descendant, 7th House sign, and major planets in the 7th House. The method, data dependencies, and limits are documented below so the result can be checked.
Method reviewed by Paul · Last reviewed July 28, 2026
Birth Chart Calculator
Calculate your relationship axis
Enter the place, date, and local time shown on your birth record. Select a city suggestion so the calculator can use its coordinates and historical timezone.
What the result includes
A focused chart snapshot, not a complete natal reading
Sun, Moon, and Rising
A compact view of solar identity, lunar needs, and the sign rising on the eastern horizon.
Ascendant and Descendant
The exact chart axis used to orient the 1st and 7th Houses.
7th House sign
The sign on the Placidus 7th House cusp, used as the starting point for relationship interpretation.
Major planets in the 7th
Sun through Pluto only. Chiron, nodes, asteroids, and calculated points are not labeled as planets.
Calculation defaults
The settings used on this site
The calculator uses the tropical zodiac and Placidus houses. It creates the chart in the browser with circular-natal-horoscope-js. The birthplace is converted to latitude and longitude, and local civil time is interpreted in the selected IANA timezone.
City suggestions and reverse geocoding come from OpenStreetMap Nominatim. Coordinate-based timezone lookup uses TimeAPI. The browser performs the chart calculation after those inputs are available; this site does not require an account to calculate a snapshot.
If you compare the result with another tool, first match zodiac, house system, coordinates, time, and timezone. A Whole Sign chart can assign planets to different houses without changing their zodiac positions.
Accuracy limits
The result is only as precise as the birth data
The Ascendant and Descendant move throughout the day. A rounded or remembered birth time can change their degrees, and a larger error can change the sign or move a planet across a house cusp. Historical daylight-saving rules also matter.
If your time is uncertain, calculate the earliest and latest plausible times and compare the results. See the birth-time accuracy guide before treating a cusp-sensitive placement as fixed.
Reproducible examples
Sample inputs used to check the calculator
These examples use city-center coordinates returned for each selected place. Small coordinate differences can change degrees without necessarily changing the signs shown here.
London, United Kingdom
Input: January 1, 1990 at 12:00, Europe/London
Expected snapshot: Sun Capricorn, Moon Pisces, Aries Rising, Libra Descendant, Pluto in Scorpio in the 7th House.
New York, United States
Input: June 15, 1988 at 18:30, America/New_York
Expected snapshot: Sun Gemini, Moon Cancer, Sagittarius Rising, Gemini Descendant, with Sun, Mercury, and Venus in the 7th House.
Shanghai, China
Input: September 9, 2019 at 09:09, Asia/Shanghai
Expected snapshot: Sun Virgo, Moon Capricorn, Scorpio Rising, Taurus Descendant, with Uranus in Taurus in the 7th House.
Interpretation boundary
What this calculator does not claim
- It does not predict whether, when, or whom you will marry.
- It does not assess compatibility between two complete charts.
- It does not replace a full reading of the 7th House ruler, aspects, Venus, Moon, and repeated patterns.
- Astrology is interpretive and should not replace medical, legal, financial, or mental-health advice.
Article Information
Paul documented the calculator settings, checked the sample cases, and reviewed the interpretation and accuracy limits on this page. Published by HouseRuler. See About, Editorial Policy, or contact support.
References
Calculator data and methodology references
These are the outside services and references used to explain the calculation inputs, timezone handling, and house-system choices.
OpenStreetMap
Nominatim Usage Policy
Documents the public geocoding service used for city suggestions and coordinates.
IANA
Time Zone Database
The timezone identifier and historical rule framework used by modern timezone libraries.
Astrodienst
The Astrological Houses
Background on house systems and why planet house assignments can differ between calculators.
circular-natal-horoscope-js
Open-source calculation library
The browser-side library used to calculate tropical positions and Placidus houses.