Birth Chart Calculator: Planets, Signs and Houses — Free, No Sign-Up

A birth chart is the diagram of the sky for the moment and place a person was born. In the chart the Sun, the Moon and eight planets each sit at a particular degree of a sign in the tropical zodiac; when the birth time is known, those placements also spread across twelve houses and a rising sign appears on the horizon. The Sun sign is only one line of that chart: two people born on the same day share a Sun sign while their Moon sign, rising sign and house layout differ. In astrology a chart is not a personality test but an order whose layers are read together.

The calculation rests on two inputs. The date and time, together with the time zone of the birth place, become one universal moment; the latitude and longitude then decide which sign was rising on the horizon and where the house boundaries fall. That is why two people born at the same instant in different cities share planet signs but not rising signs or houses.

A birth chart is three separate layers stacked on top of each other. Each layer answers a different question and asks for different birth data.

1. The birth date and time are converted, using the time zone of the birth place, into a single universal moment of sky.
2. Each body's ecliptic longitude for that moment is found with an astronomical calculation engine; the 30-degree slice the longitude falls into gives the sign, and the position inside that slice gives the degree.
3. The latitude and longitude of the birth place, together with local sidereal time, give the rising sign and the midheaven.
4. House boundaries are drawn with the Placidus system and every planet is placed in the house it falls into.

The rising sign changes roughly every two hours and the house boundaries shift continuously. Without a birth time those two layers cannot be calculated. The tool accepts a time-less calculation but leaves the missing parts empty: no rising sign or midheaven row is written and the house column stays blank. The Moon also moves about thirteen degrees a day, so on the days it changes sign the Moon sign depends on the time too; where that happens the tool names both possibilities and does not choose between them.

• Calculated: the sign, degree and retrograde state of ten planets.
• Not calculated: the rising sign, the midheaven, the twelve house boundaries and the house placements.
• Not certain: bodies that change sign during the birth date — the tool marks these separately.

There are three known reasons two sites produce different charts from the same birth details, and all three are choices rather than errors.

The first is the house system: this tool uses Placidus, which is the most common choice. Systems such as Whole Sign or Koch draw the house boundaries elsewhere, so planet signs stay the same while house numbers can change.

The second is calculation precision: here positions are computed astronomically for the birth moment. Sites working from rounded tables can drift at the minute level, and when a planet sits on a sign boundary that drift can change the sign itself.

The third is the time zone: daylight saving rules in past years differ from country to country and year to year. Convert the birth moment with the wrong offset and the rising sign and houses shift. This tool uses the IANA time zone of the birth place and applies the rule that was in force on that date.