Private astrology calculator
Find your Big 3: Sun, Moon and rising sign
Your birth details
Enter your birth details
The birth city sets your local time zone.
Your Big 3 are your Sun, Moon and rising signs — the placements that shape a chart's tone the most; enter your birth date, time and city and all three are calculated here, in your browser. Without a birth time you still get the Sun and Moon, and the rising sign for each two-hour window of that day.
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✦ Birth chart Opens with this chart already loaded. Nothing travels in the URL.Direct answer
What you need
Birth details are never placed in the URL or sent for calculation. They stay in this browser, which remembers them for next time unless you choose Don’t remember; Keep this chart saves them to an account only if you press it.
Method & limits
Astronomy first, symbolism second.
Calculations use the tropical zodiac and geocentric apparent ecliptic positions. A rising sign cannot be calculated responsibly without an exact time and place; near a sign boundary, a small input error can change the result.
In short
- Computes
- Your Sun, Moon and rising signs, the Big 3, from one birth moment.
- You enter
- Birth date, time and city.
- You get
- All three signs and a full chart wheel; with no time, the Sun and Moon plus the rising sign for each two-hour window.
- Accuracy
- Astronomy Engine positions; the rising sign depends on the exact time and place.
Checked
Frequently asked questions
How accurate is this Big 3 calculator?
The Sun and Moon signs come from Astronomy Engine to within about one arcminute of precision for the date and time you enter, and the same is true of the rising sign once a birth time and place are supplied. The rising sign is the most sensitive of the three to a small error in the recorded time.
What happens if I do not know my exact birth time?
If the Sun or the Moon changed sign during your birth date, both possible signs are shown, with the range each one covered that local day; otherwise the one sign held all day. The rising sign needs a clock time, so instead the page lists the sign that was rising in each two-hour window of that day at your birthplace, and the Estimate with sunrise option can add an approximate Ascendant, marked as an estimate.
What is a cusp birthday, and which of my three signs does it affect?
A cusp birthday usually refers to the Sun, when your birth date falls close enough to a sign change that the exact hour and time zone decide it. The Moon changes sign roughly twelve times a month and the rising sign roughly every two hours, so both are far more likely to sit on a cusp than the Sun is.
Does this use the tropical or sidereal zodiac?
All three signs here use the tropical zodiac, the seasonal system where zero degrees Aries marks the spring equinox, rather than the sidereal zodiac, which is anchored to the visible constellations. Most Western astrology, including the Big Three idea, is built on the tropical convention.
Why do I need to enter a birthplace for my Big 3?
The birthplace sets the historical time zone that converts your entered local time into the correct astronomical instant, and it sets the horizon the rising sign is measured against. Without it, the Sun and Moon signs can still be calculated, but the rising sign cannot. For a birth before 1970 in a small set of zones — mostly the Low Countries, Scandinavia and the former Yugoslavia — the historical rules come from the tzdata backzone (release 2025c), compiled into the site.
Is my birth information sent anywhere?
No. The calculation runs entirely in your browser using a local astronomy library and an offline city list; birth details are not sent for calculation or placed in the URL. This browser remembers them on this device for next time unless you choose Don’t remember, and Forget removes them. If you choose Keep this chart, its birth details are saved to your optional account until you delete them.