Calculate your birth chart for free.

Why the birth time matters this much

The Ascendant is the sign rising on the eastern horizon at your birth moment. A time error changes its degree and the house cusps; its rate varies with latitude and the sign rising. A two-hour error cannot be reduced to one fixed sign shift.

The Moon moves about 13 degrees a day. Without a birth time, its degree and sometimes its sign are uncertain. The Sun and planets move more slowly, but on the day they change signs their signs may also depend on the time.

A chart without a birth time can still be useful. Baby Astro compares placements at the beginning and end of the local day, showing signs that stay stable and two possibilities where a boundary is crossed. We do not draw an exact-degree wheel or aspect table from an arbitrary noon estimate.

How historical time zones affect a chart

A chart is computed by converting your birth moment into universal time, which requires knowing the offset that was actually in force in that country on that date — not the one in force today.

Here is a checkable example. At noon on 15 January 1990 in Istanbul, winter time was UTC+2, so the birth instant was 10:00 UTC. Applying today's fixed UTC+3 to that old birth would make it 09:00 UTC instead. Casting the chart an hour early shifts the Ascendant degree and house cusps. On 15 July 1990, summer time was UTC+3, so today's offset happens to be correct for that date.

The Baby Astro web calculator uses the historical time-zone offset when the browser supports that data. If it does not, the local engine falls back to an approximate longitude-based offset; do not treat that result as exact. Check your birth time and city, and compare a chart whose Ascendant you already know.

Source: IANA Time Zone Database, 2016g release notes

How is this birth chart calculated?

The free web chart uses the tropical zodiac of Western astrology. After converting your birth moment to UTC, we calculate the Sun, Moon and planets' Earth-viewed positions in your browser with Astronomy Engine. AI chat does not supply the planetary positions. A planet's sign tells you which 30-degree segment contains its calculated longitude; interpretation comes afterward.

With a known birth time and selected city, we also calculate the Ascendant and houses. Placidus is the default house system; beyond roughly 66 degrees of latitude, the calculation falls back to Whole Sign houses. There is no house-system selector on web yet. Without a birth time, we do not show an exact rising sign or house placement.

To compare your result with another chart, start by matching the birth time and city. Then check that both use the tropical zodiac and the same house system. Near a sign boundary, a timezone difference or even a few minutes in the input can change the result. Matching numbers are a calculation check, not proof that one interpretation is better.

Source: Astronomy Engine: JavaScript / TypeScript API

What happens once the chart is computed

The raw chart is a data table: ten planets, twelve houses, a dozen aspects. On its own it tells nobody anything. Interpretation is the hard part — and it is where most apps either bury you in jargon or write sentences vague enough to fit any chart.

In Baby Astro you can see the basic placements and first interpretation for free. More detailed readings are part of Astro-Plus; you see the current subscription price before choosing a paid step.

The chart is computed once and never changes — your birth moment does not move. What moves is the sky: transits touch your fixed chart every day, and that is where the daily guidance comes from.