A natal chart is a map of the sky at the exact moment you were born: where the Sun, Moon, and the rest of the planets were, in which sign and in which house. Unlike a horoscope written for "all Aries," a natal chart is calculated once, for one specific person, in one specific place, at one specific minute — which is why it's different for everyone, even people born on the same day.
Three things are needed for the calculation: birth date, birth time, and birth city. Date and place determine which zodiac signs the planets were in — the most stable part of the chart, one you can build even without an exact time. Birth time is needed for something else: it determines which degree of the zodiac was rising on the eastern horizon at the moment of birth — that's the ascendant, more on its calculation separately — and, in turn, where the boundaries of the twelve houses fall. Without an exact time, the houses and ascendant are honestly unavailable — not roughly estimated, genuinely unavailable: where there's no precision, it's better not to pretend there is.
Planets in signs answer the question "what am I like" — the Sun, Moon, Mercury, Venus, and the rest of the planets in a given sign describe different layers of personality: not just character, but how you think, love, make decisions. Houses answer the question "in which area of life does this show up" — work, relationships, home, travel. And aspects between planets show how these layers interact with each other: reinforcing one another or creating internal tension.
The difference between an accurate calculation and an approximate one isn't a small thing. Many free calculators online round planetary positions or use simplified tables. Here the calculation runs on real astronomical ephemeris data, cross-checked against independent sources (NASA JPL Horizons) to within arcseconds — far more precise than astrology actually needs, but honest about it. What that precise data means for you personally is written by a language model on top of it — worth treating as a tool for thinking about yourself, not a prediction.
Build your natal chart for free — you'll need a birth date, and you can add the time and place later if you don't know them precisely yet.