How We Calculate

Every calculator on Astrolivo uses the same calculation engine. This page explains how it turns your birth date, time and city into a chart, where it has limits, and who is responsible for the texts you read.

Planet positions come from an ephemeris, a table of where the Sun, Moon and planets are at any given moment. Planet positions are calculated from NASA JPL DE440 ephemeris via Skyfield. We check the results against Swiss Ephemeris, an independent reference used by many astrology programs: on 91 test charts, planet positions agree to within about two arcseconds, most of them to within one, and the Ascendant, Midheaven and house cusps to within 14 arcseconds away from the polar circles. That is far finer than the one arcminute a chart shows.

Charts use the tropical zodiac, which measures the signs from the March equinox. This is the zodiac used in most Western astrology. When a birth time is provided, Astrolivo calculates the Ascendant, Midheaven, and twelve houses using the Placidus house system (above about 66° latitude, where Placidus is undefined, the houses are shown in the Whole Sign system with a visible label), and measures five major aspects—conjunction (0°), sextile (60°), square (90°), trine (120°), and opposition (180°)—between the ten core bodies (Sun through Pluto) using a uniform maximum orb of 6°. One orb serves every aspect and every planet, the Sun and Moon included: astrologers disagree about wider orbs for the lights, and a single rule lets you check any listed aspect against the degrees shown. The same settings apply in the birth chart, rising sign, moon sign and big three calculators. That is why your Sun, Moon and rising sign match from one page to another.

The calculation is an astronomical one. What the positions mean is a matter of reading, and different astrologers read them differently: astrology is a tradition of interpretation, not a science.

A birth chart needs an exact moment, and the time on a birth certificate is local time. To convert it, the calculator needs to know the time zone that applied at your birthplace on your birth date. Time zones and daylight saving rules have changed many times, so we use the IANA time zone database, which keeps those historical rules, instead of today's offset. For a birth before 1970 with a known time, if you know the local clock differed from what the database gives, you can set the UTC offset yourself; the result then shows "offset set by you".

You choose your birth city by starting to type and picking it from the suggestions. The place sets the time zone and the location of the horizon, which the rising sign and houses depend on.

The sign-change times in our birthday tables are given to the minute, without seconds, and converted to local time with the same historical time zone rules. If you were born within a minute or two of a change, check your sign with the birth chart calculator.

Tick "I don't know my birth time" and the calculator still builds a chart. The chart uses a noon reference on your birth date, marks the result as unknown-time, and hides the rising sign (Ascendant), Midheaven (MC), houses, exact degrees, and aspects because they depend on an exact birth time.

Instead of relying on a single noon position, the calculator checks for any sign changes across your entire local birth date. If the Sun, the Moon, or another planet changes sign during that local day, the result shows each possible sign for that day rather than guessing a single one.

We don't make medical, financial or legal predictions, and we don't tell you what will happen in your life. Astrology here is offered as a way to reflect, not as advice for decisions about your health, money or legal matters.

Birth data is personal. How we store it and how you can delete it is described in the privacy policy.

Build your birth chart, or read How to read a birth chart first.