Birth Chart Calculator

How this calculator actually works

Unlike the sun-sign-only Personal Horoscope tool, this calculator computes real ecliptic positions for the Sun and Moon, and the Ascendant (Rising sign) from your exact birth time and location — using standard astronomical formulas for solar and lunar longitude, Greenwich Sidereal Time, and the ascendant equation. It is not a static lookup table.

What "Sun," "Moon," and "Rising" mean

• Sun sign — where the Sun sat in the zodiac on your birth date. This is what most people mean by "their sign," and only needs your birth date.
• Moon sign — where the Moon sat at your exact birth time. The Moon moves through the entire zodiac roughly every 27.3 days — about one sign every 2–3 days — so it needs a real birth time to calculate.
• Rising sign (Ascendant) — the zodiac sign on the eastern horizon at the moment and place you were born. It's the most time-sensitive of the three: it changes roughly every two hours, so an inaccurate birth time can shift it by an entire sign.

On precision

The Sun position used here is accurate to a small fraction of a degree — reliable for determining a sign in virtually every case. The Moon calculation uses the dominant terms of a standard low-precision lunar formula and is accurate to roughly a degree in typical cases; if your birth moment falls very close to a sign boundary (within a few hours of the Moon changing signs), it's worth double-checking against a professional ephemeris. The Ascendant is mathematically exact given your inputs, but is only as accurate as the birth time and location you provide — a birth time that's off by 10–15 minutes can occasionally shift it into a neighboring sign.

House placements

Below your Sun, Moon, and Rising, this calculator also shows your full 12-house breakdown in two systems — Whole Sign and Equal House — along with which house your Sun and Moon each fall into. Both systems are calculated directly from your Ascendant, the same verified placement used for your Rising sign. Read more about what houses represent in Astrological Houses: A Beginner's Guide.

What this isn't

This calculator doesn't include the positions of other planets (Mercury, Venus, Mars, and beyond) or aspects between planets, and it doesn't yet calculate Placidus houses — the time-divided system most professional software defaults to, which involves a meaningfully more complex calculation. Think of this as the "big three" plus a real house framework, not yet a complete professional chart.