About Birth Chart Now: How the Charts Are Calculated

What this site is

Birth Chart Now is a small independent project, built and maintained by one developer rather than a company. It offers a birth chart calculator, a North Node calculator, a solar return chart, a Venus sign calculator and a Saturn return calculator. They are free to use and need no account.

The calculations run in your browser. Your birth date and time are not sent to our servers, and saved charts stay on your device. The privacy policy lists exactly what does reach a server.

How the charts are calculated

Positions. The Sun, Moon, planets and Chiron come from the caelus ephemeris, which uses the VSOP87 theory for the planets and analytic series for the Moon and Pluto. The true lunar node comes from Astronomy Engine. All positions are tropical and geocentric.
Time zones. The local time you enter is converted to Universal Time with the time zone database built into your browser. The page always shows the UTC offset it used, and you can change it if your records say otherwise.
Houses. Placidus or Whole Sign. Placidus can't be calculated close to the poles, so for birth places beyond about 66° latitude the calculator switches to Whole Sign and says so.
Degrees. Positions are shown within each sign and cut off at the minute, not rounded, so 19°36.9′ is shown as 19°36′.
Aspects. Conjunction and opposition with an 8° orb, trine and square 7°, sextile 5°. The orb is halved for the North Node and Chiron and widened by 1° when the Sun or Moon is involved.

How accuracy is checked

Every change to the calculator is tested against Swiss Ephemeris 2.10, a reference ephemeris widely used by professional astrology software. The test draws 300 random charts between 1900 and 2049, at birthplaces between 60° south and 60° north, and compares each position.

In the latest run the largest difference for the Moon was 13 arcseconds and for the true node 18 arcseconds. The Sun, the planets, Chiron, the Ascendant, the Midheaven and the Placidus house cusps all agreed within about 2 arcseconds. One arcminute is 60 arcseconds, so none of these differences changes a displayed degree or minute except, very rarely, when a position falls right on a minute boundary.

Known limits

Birth dates from 1900 to 2099.
Time zone records before 1970 are less complete for some places. A few European cities, for example Oslo in the early 1960s, can come out an hour off. The page warns you for any birth before 1970 and lets you enter the correct offset.
Birthplace search covers places with about 1,000 or more inhabitants. If a village isn't listed, choose the nearest town: for a chart, the time zone and rough location are what matter.
Without a birth time, the chart is set for local noon and no houses or rising sign are shown. The Moon can then be up to about 7.5 degrees off.

About astrology

Astrology content on this site is for entertainment and self-reflection only. It does not predict events and is not a substitute for medical, legal, financial or other professional advice.

The positions on this site are astronomy: anyone with the same birth data and a correct ephemeris gets the same numbers. The meanings attached to them come from astrological tradition, which differs between schools and is not supported by scientific evidence.

Contact

Found a chart that looks wrong, or a mistake on a page? Get in touch.

Data and open-source licenses

This site uses the following open-source software:

caelus, for planet, Moon, Chiron and house calculations. MIT License.
Astronomy Engine, for the true lunar node. MIT License, Copyright (c) 2019-2023 Don Cross.
AstroChart, for drawing the chart wheel on the results page. MIT License, Copyright (c) 2015-2018 Matheus Alves.

The PDF report uses the fonts Spectral, IBM Plex Mono and Noto Sans Symbols, licensed under the SIL Open Font License 1.1 (Copyright 2017 The Spectral Project Authors; Copyright 2017 IBM Corp.; Copyright 2022 The Noto Project Authors).

MIT License text

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.