Calculate your birth chart

A birth chart (also called a natal chart) is a map of where the Sun, the Moon, and the planets were at the exact moment and place you were born. Astrology reads that map through twelve signs, twelve houses, and the geometric angles between planets (aspects). At MoonSignal we treat it as a mirror for self-reflection — a way to name tendencies and patterns — not as a prediction of what will happen.

Yes. No account, no email, no card. Enter your birth date, time, and place and you get your full chart: planet placements, houses, aspects, and your Sun, Moon, and Rising signs.

No. This page computes your chart entirely in your browser. Your birth data is never sent to our servers, logged, or saved. If you later take the quiz and build a Pattern Blueprint, we store your birth data under your account. You can delete it at any time.

You can check the "I don't know my birth time" box. We then calculate the sky for midday. The signs of your Sun and planets stay accurate, because they move slowly through the day. Your Rising sign and house placements need an exact time. The Moon changes sign every two to three days, so if it sits near a sign boundary that day, we flag it rather than guess.

The Rising sign changes roughly every two hours. So it is very sensitive to your birth time, and to how a calculator handles old time zones and daylight saving. If two sites disagree, it helps to confirm that both use the same birth time. You can also shift the time by one hour: a DST mismatch is the most common cause.

Placidus, the one most Western astrologers use. Some popular apps use Whole Sign instead, so the same planet can end up in a different house. The sign of your planet does not change between the two; only the house lines do. Near the poles, where Placidus does not work, we fall back to Porphyry.

A horoscope is written for everyone who shares one sun sign, one twelfth of the population. A birth chart is computed from your exact birth date, time, and place. So it is specific to you: your Moon, your Rising, your houses, your aspects. Two people with the same sun sign can have very different charts.

A chart lists placements. The useful part is what those placements tend to do in real life. MoonSignal maps your chart plus a two-minute quiz to 12 named behavioral patterns across relationships, career, and self-worth. Each comes with the tendency, the strength inside it, and a small shift to try. That part is free for you in early access.

The astronomy is not in dispute: where the planets were at a given moment is the same for every serious calculator. When two charts disagree, the difference almost always comes from one of three places — how the calculator divides the sky into houses, how it resolves the time zone and daylight saving rules that applied at your birth, or which convention it uses for points like the lunar node. Aspect lists diverge for a separate reason: every calculator sets its own maximum orb — how far from exact an angle may sit and still count — so one app can name ten contacts in a chart where another names sixteen. Ours are deliberately tight, and the limit narrows with the bodies involved: the Sun, the Moon and the Ascendant carry the widest margin — 8° for a conjunction — while a contact to a slow outer planet is held closer to 6°. Two things we leave out on purpose: quincunxes, and contacts between only the slow-moving planets, which describe a generation rather than a person. If an app you've used shows a contact we don't, that is usually why.

Planet positions are computed with a professional-grade astronomical ephemeris, checked against events whose timing is independently known — equinoxes, solstices, a total solar eclipse — and, for Chiron, against NASA JPL Horizons data. We use the tropical zodiac, apparent geocentric positions and the true lunar node — the same conventions used by astro.com and most Western astrologers, so your placements will match the references astrologers actually use. Time zones and daylight saving are resolved from the historical time zone database for your exact birth date and place, down to the minute. The ephemeris we ship covers births from 1900 to 2098 — outside that window we refuse the date rather than extrapolate a position we can't stand behind. And the whole calculation runs in your browser: the only thing that leaves your device is the name of your birth city, sent to a public geocoding service to look up its coordinates and time zone. Your birth date and time are never sent anywhere.

We use the Placidus house system, the most widely used one in Western astrology. Some popular apps use the Whole Sign system instead, where each house spans exactly one sign. Both are valid. They draw the twelve house lines differently, so a planet close to a line can sit in one house here and in the next house in another app you use. The planet's sign never changes; only the house does. Near the poles, where Placidus does not work, we fall back to Porphyry, as most do.

The usual suspect is the birth time. Rising signs change roughly every two hours, and a one-hour daylight-saving discrepancy is enough to shift yours. If your Rising sign doesn't match what you expected, try moving your birth time one hour forward or back. If the birth time itself is what you're missing, we wrote a guide to tracking it down. If you don't know your birth time at all, we calculate the sky for midday and say so. The signs of your Sun and most planets stay reliable. The Rising sign and houses wait until you have a time. The Moon is the exception: it moves fast enough to change sign within a day. So when it falls near a boundary, we flag it rather than guess. We also leave its aspects off the list until you have a time, rather than print an orb we would have had to invent.

A birth chart describes tendencies: how you tend to move, react, attach, and protect yourself. It does not predict events. It does not guarantee outcomes, and it is not therapy. We treat it as a map for self-reflection, useful for naming the loops you already half-recognize in yourself. If you want to see what your placements tend to do in real life, that's what the pattern library and your personal Blueprint are for.