Birth chart guide

Birth chart without birth time: what can you know?

You can calculate a partial chart from your birth date and place. You cannot recover an exact birth instant from those details. Some sign labels stay the same all day; others can change. Starlit Chart marks that difference instead of supplying a guessed Rising sign.

Known, approximate or unknown?

If you have a recorded local time, enter it as written and select the birthplace. Do not subtract daylight saving time yourself: the time zone conversion handles the clock offset. A remembered “around breakfast” time is approximate, even if a form accepts it. Try alternative plausible times separately and treat changes cautiously.

For no usable time, check I don't know in our free form. We use local noon as a calculation anchor. Noon is not evidence that you were born then, and the displayed degrees are not exact birth positions.

Three kinds of result

• Sign stable across the checked day: a body remains in the same zodiac sign at our sampled times. That does not make its exact degree known.
• Sign uncertain: a body crosses into another sign. The Moon is a common example; another planet close to a sign boundary can change too. Even the Sun can be uncertain near a sign change.
• Unavailable: the Ascendant (Rising), Midheaven, houses and chart ruler need a time. We omit them rather than assume noon houses.

A reproducible fictional example

Jordan is an illustrative name, not a customer: May 14, 1991, Denver, Colorado (39.73915° N, 104.9847° W), America/Denver time zone, time unknown. The noon anchor resolves to 1991-05-14T18:00:00.000Z. These values are generated by the same engine as the free chart.

How the uncertainty check works

We convert the birth date's local 00:00 and 23:59 into instants using the birthplace time zone. The engine samples Moon signs every two hours and other bodies every six hours, including the endpoints. A sign change marks that body's sign uncertain. This is a sampled check, not an exact Moon-ingress calculator or a minute-by-minute proof.

Moon aspects in an unknown-time chart are marked time-sensitive. An aspect is an angular relationship between two positions: as the Moon moves, an apparent relationship may tighten, loosen or fall outside our allowed range. Non-Moon aspects are noon calculations too; the absence of a warning does not establish an exact birth degree.

If you find a time later

Check a birth record or ask someone who was present, while allowing for rounding or memory errors. Make a new free chart with the recorded time; sign in first if you already bought a reading. You can compare the new Moon, Rising and houses with the earlier partial chart. We do not infer or “rectify” your time from personality descriptions.

For house conventions, read Placidus vs Whole Sign. The help page explains access to a new chart after purchase.

Sources and limits

The IANA time zone database documents historical clock changes. NASA JPL Horizons provides astronomical ephemerides; it is a reference for positions, not evidence for astrological interpretations. The example and sampling description above document our own engine.

Try your own details

Get your free birth chart. The form asks for your name, date and birthplace, plus your recorded time if known. No email is needed to see your chart. The optional full reading costs $37; start with the free result and its uncertainty notes.

For entertainment and self-reflection. Calculating astronomical positions does not validate astrology's personality claims or predict events.

Reviewed October 13, 2026.