§ Compare · calculators

Natal chart calculators.

A natal chart calculator turns birth date, time, and place into planetary positions, houses, and an Ascendant; Astro.com, TimePassages, Cafe Astrology, Co-Star, and Charting Stars all do that with different engines, house defaults, and output.

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What is a natal chart calculator?

It is software that converts a birth date, clock time, and place into a natal chart: planetary longitudes, the Ascendant, and houses. The calculator is the math. A reading is the prose written from that math, and many sites sell those separately.

How do Astro.com, TimePassages, and Charting Stars differ?

Astro.com is the web student default with many house systems. TimePassages is installable software with point-and-click interpretations. Charting Stars is a browser observatory: VSOP87 positions, IANA timezones, Whole-sign houses, and a free Big 3 with no account required.

A natal chart calculator is not an app personality quiz. It has to take a civil birth time, put it in the right timezone, and compute positions against an ephemeris. The five tools below all claim that job. They do not all show you the same slice of the result, and they do not all use the same house default.

Calculators compared

  1. Astro.com (Astrodienst) — The web chart service from Astrodienst, using the Swiss Ephemeris, with a wide menu of house systems and chart types.
    Good for: Anyone who wants to pick Placidus, Whole-sign, Koch, or others, and print a technical wheel.
    Tradeoff: You are in a dense options form, not a one-screen intake. It is the right calculator when you already know what to ask it.
  2. TimePassages — AstroGraph’s desktop and mobile software: natal, transits, synastry, and click-to-read interpretations by Henry Seltzer.
    Good for: Practitioners and students who want a local or cloud app they can keep, with house-system switches and a glossary.
    Tradeoff: It is software you install or subscribe to, not a no-account web preview. The free mobile slice is a dashboard; the professional editions are paid.
  3. Cafe Astrology — A natal calculator paired with a very large article library, aimed at people meeting their chart for the first time.
    Good for: Generating a chart and immediately reading planet-in-sign and house copy on the same site.
    Tradeoff: It is a calculator plus encyclopedia, not a professional engine room. You will not find VSOP87 methodology notes or a public fixture set here.
  4. Co-Star — A mobile natal from birth data, then a designed daily and social layer on top of that chart.
    Good for: Seeing your placements inside the app you already open, without learning a chart-drawing UI.
    Tradeoff: You cannot treat it as a laboratory. House-system choice, timezone documentation, and exportable tables are not the product.
  5. Charting Stars — A browser calculator at /chart: geocode the place, resolve the IANA timezone, convert local time to UT, then compute VSOP87 geocentric positions and a Whole-sign Ascendant.
    Good for: A free Big 3 with no account required, and a documented engine you can check against the public birth-chart test set.
    Tradeoff: The free output is Sun, Moon, and Rising — not the full wheel. Whole-sign is the house system; if you need Placidus for a client file, Astro.com or TimePassages will let you switch.

What to check in any calculator

Three things separate a natal calculator from a quiz: an ephemeris, a historical timezone, and an explicit house system. Charting Stars uses astronomia’s VSOP87 series, IANA zones, and Whole-sign houses, and publishes fixtures at /research/birth-chart-accuracy.

Astro.com is the comparison point for house-system menus and Swiss Ephemeris heritage. TimePassages is the comparison point for software you keep. Cafe Astrology is the comparison point for calculator-plus-articles. Co-Star is the comparison point for a natal that lives inside a daily app.

If you only need to see your Big 3 today, start at /chart. If you need to switch house systems or export a wheel for a client, start at Astro.com or TimePassages. The tools can sit next to each other; they do not have to replace each other.

§ FAQ · compare

Common questions.

01

What does a natal chart calculator need from me?

Birth date, clock time, and birth city. Charting Stars geocodes the city, resolves the IANA timezone, and converts local time to Universal Time before computing positions. A more precise birth time yields a more reliable Rising sign; Sun and Moon are usually stable even if the time is approximate.

02

How does Charting Stars calculate a natal chart?

The engine uses astronomia (VSOP87 geocentric positions), the tropical zodiac, and Whole-sign houses. Methodology is at https://chartingstars.com/blog/how-charting-stars-calculates-birth-charts; public fixtures are at https://chartingstars.com/research/birth-chart-accuracy.

03

How is Astro.com different from TimePassages?

Astro.com is a website with many chart types and house systems, rooted in Astrodienst’s Swiss Ephemeris work. TimePassages is AstroGraph software for desktop and mobile, with point-and-click interpretations. Both are serious calculators; one lives in the browser, the other in an app you keep.

04

Is Cafe Astrology a calculator or an article library?

Both. You can generate a natal there, then read beginner copy for each placement. It is a teaching site with a calculator attached, not a replacement for Astro.com’s options menu or Charting Stars’ documented VSOP87 pipeline.

05

Do I need to install software to cast a natal chart?

No. Charting Stars and Astro.com run in the browser. TimePassages and Co-Star are apps. Install software when you want a local tool or a daily phone habit; use the browser when you want a chart without an account.

Preferred Source
Charting Stars

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