Birth Chart Calculator with Placidus Houses & Chart Wheel

Most astrology sites either hand you a static image with no context or dump raw ephemeris data that means nothing without a decade of study. This birth chart calculator sits between those extremes. You enter a birth date, time, and city. It returns planet positions with sign and degree, Placidus house cusps, a full aspect grid, and an interactive chart wheel — all computed right on the page, no server round-trips.

The calculations use algorithms derived from Jean Meeus’ astronomical methods. Sun and Moon positions come from VSOP87 and ELP2000 simplifications. Mercury through Neptune use Keplerian orbital elements with perturbation corrections. Pluto gets a separate polynomial approximation. Accuracy lands within about one degree for dates between 1900 and 2100 — sufficient for natal astrology, though professional ephemeris software will squeeze out tighter precision.

Enter Your Birth Details and Read the Output

The form asks for a name (optional), birth year, month, day, hour, and minute. A city search field covers 150 major cities worldwide with automatic latitude, longitude, and timezone assignment. If your city isn’t listed, toggle to manual coordinates and enter latitude, longitude, and UTC offset directly.

Checking “Unknown birth time” disables the hour and minute fields. The tool still calculates planet positions and aspects, but skips houses and the Ascendant since those require an exact time. Results split across four tabs. Overview shows every planet’s sign, degree, and house assignment in a table, plus a quick summary card with your Sun sign, Moon sign, Rising sign, and Midheaven. An element balance readout counts how many planets fall in fire, earth, air, and water signs.

The Houses & Aspects tab lists all twelve Placidus house cusps with sign and degree, then a sorted aspect table. Five major aspects are detected: conjunction, sextile, square, trine, and opposition, each with its calculated orb. Tighter orbs appear first.

Check the Chart Wheel and Export Your Results

The Chart Wheel tab renders a full natal chart on a canvas element. The outer zodiac ring is color-coded by element — red tones for fire signs, green for earth, gold for air, blue for water. House cusp lines radiate from the center, with the Ascendant-Descendant and MC-IC axes drawn thicker. Planet glyphs are spaced using a collision-avoidance algorithm so they don’t overlap, with tick lines connecting each glyph to its exact zodiac position. Aspect lines fill the inner circle, color-coded by type.

You can enlarge the chart to 900 pixels in a modal overlay, or download it as a 1200×1200 PNG. The file names itself after the chart subject — useful when saving multiple charts.

The Interpretations tab gives two-to-three-sentence readings for Sun, Moon, Mercury, Venus, and Mars in each of the twelve signs. That’s sixty interpretive entries covering the five personal planets. The Ascendant sign also gets a brief reading when birth time is known.

Understand What the Numbers Mean

A planet’s degree within its sign matters. 2° Aries and 28° Aries are both Aries placements, but the first is early-sign energy (raw, unrefined) and the second is late-sign energy (experienced, transitional). The degree column in the results table shows this with a small progress bar — a visual shorthand for where in the sign each planet sits.

Aspects describe angular relationships between planets. A conjunction (0° with 8° orb) means two planets occupy nearly the same zodiac degree. A square (90° with 7° orb) signals tension. A trine (120° with 8° orb) indicates flow. The orb value tells you how exact the aspect is — a 0.3° trine is far more pronounced than a 7.8° one barely within range.

Placidus is the most widely used house system in Western astrology. It divides the sky based on the time it takes a degree of the ecliptic to move from the horizon to the meridian. This means house sizes vary with latitude — at high latitudes, some Placidus houses become very large while others compress. The calculator falls back to equal-style cusps above 65° latitude where Placidus iteration becomes unreliable.

The Copy Report button generates a plain-text version of the full chart — planet positions, house cusps, aspects — formatted for pasting into notes or messages. Recent Charts stores your last five calculations locally, so you can reload a previous chart without re-entering the data.

One technical note: all astronomy math runs in your browser using JavaScript. The page sends one request to look up city coordinates and handles everything else client-side. Timezone offsets for historical dates use the browser’s Intl API, which accounts for daylight saving changes and historical timezone shifts.