Birth Chart Calculator
Enter your birth date, time and city to draw your natal chart: where the Sun, Moon and planets were, your Rising sign, the 12 houses and the main aspects. Everything is calculated in your browser.
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Birth chart
Astrology is for entertainment and self-reflection. Positions are tropical (Western) zodiac, geocentric, accurate to a few arcminutes; the Moon moves about 0.5° per hour, so an exact birth time matters for the Moon degree, Ascendant and houses.
How to use the Birth Chart Calculator
- Enter your birth date and, if you know it, the exact birth time from your birth certificate.
- Choose your birth city from the suggestions, or click Enter coordinates instead and type latitude, longitude and time zone.
- Pick a house system (Placidus is the most widely used) and press Calculate chart.
- Read the wheel and tables: Planets shows each sign, degree and house, Houses lists the cusps, Aspects lists the angles between planets.
- Save or share with Download PNG, Download SVG, Copy summary or Copy link.
How a birth chart is calculated
A birth chart (natal chart) is a map of the sky seen from your birthplace at the moment you were born. The calculator works in four steps:
- Local time to Universal Time. Your birth time is converted to UTC using the time zone of the birthplace, including any daylight saving time in force that day.
- Planet positions. For that instant, the geocentric ecliptic longitude of the Sun, Moon and planets is computed from their orbital elements (with the main lunar and Jupiter–Saturn perturbation terms) and measured in the tropical zodiac, where 0° Aries is the March equinox. Each 30° slice is one sign.
- Angles. Local sidereal time gives the right ascension of the Midheaven (RAMC). The Midheaven is the ecliptic degree culminating overhead, MC = atan2(sin RAMC, cos RAMC · cos ε), and the Ascendant is the degree rising in the east, ASC = atan2(cos RAMC, −(sin RAMC · cos ε + tan φ · sin ε)), where ε is the obliquity of the ecliptic (about 23.44°) and φ your latitude.
- Houses and aspects. House cusps are found with the chosen system, then the angle between every pair of planets is compared with the aspect angles below.
Major aspects and orbs used
| Aspect | Angle | Orb allowed | Traditional meaning |
|---|---|---|---|
| Conjunction | 0° | 8° | Energies blend and act together |
| Sextile | 60° | 5° | Easy opportunity, cooperation |
| Square | 90° | 7° | Tension that pushes for action |
| Trine | 120° | 7° | Natural flow and talent |
| Opposition | 180° | 8° | Polarity, balance between two sides |
Aspects involving the Sun or Moon get 2° of extra orb, as is common practice. The orb column in the Aspects tab shows how far each aspect is from exact; smaller orbs are considered stronger.
House systems compared
| System | How cusps are found | Good to know |
|---|---|---|
| Placidus | Trisects the time each degree takes to rise to the Midheaven and to set | Most common modern default; undefined above about 66° latitude |
| Whole Sign | The rising sign is the whole 1st house, the next sign the 2nd, and so on | Oldest system; MC can fall in any house from 9 to 11 |
| Equal | 12 houses of exactly 30° starting at the Ascendant degree | Works at any latitude |
| Porphyry | Divides each quadrant between the angles into three equal parts | Used here as the fallback for polar birthplaces |
Tip: the Ascendant moves roughly 1° every 4 minutes, so a birth time that is off by 15 minutes can shift it by several degrees and may change the Rising sign or the house of a planet near a cusp. Check the time on your birth certificate if you can.
Frequently asked questions
What do I need to calculate a birth chart?
Your birth date, the exact birth time and the place of birth. The date gives the planet signs; the time and place are needed for the Ascendant (Rising sign), Midheaven and houses, which move about one sign every two hours.
What if I don't know my birth time?
Tick I don't know my birth time. The chart is drawn for noon, so the Sun and slow planets are still right, but houses and the Rising sign are not shown and the Moon can be off by up to about 6 degrees, which matters if the Moon changed sign that day.
How accurate are the planet positions?
Positions are computed in your browser from orbital elements with the main perturbation terms, and refined with the astronomy-engine library when it loads. They agree with published ephemerides to within a few arcminutes, far below the precision needed to tell signs and houses apart.
Which house system should I use?
Placidus is the default in most Western astrology software. Whole Sign houses make each sign one house starting from the rising sign and are popular in traditional and Hellenistic astrology. Equal houses are 30 degrees each from the Ascendant. Placidus cannot be calculated above about 66 degrees latitude, so the tool switches to Porphyry there.
What is the Big Three?
Your Sun, Moon and Rising signs. The Sun describes your core self, the Moon your emotional needs and the Rising sign (Ascendant) the way others first see you. The Rising sign needs an accurate birth time.
Does it handle daylight saving time?
Yes. Built-in cities use the browser's time zone database, which includes historical daylight saving and time zone changes, and the offset used is shown under the chart title so you can check it. For coordinates you can pick any time zone or a fixed UTC offset.
Is my birth data stored or sent anywhere?
No. All calculations run locally in your browser. Your last chart is remembered only in this browser's local storage so it reappears next visit, and a shared link contains only the details you entered.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.