Full Birthday Analysis Calculator

Zodiac sign calculation assigns one of 12 Western astrological signs based on the position of the Sun in the ecliptic at the moment of birth. The Sun moves approximately 1° per day through the zodiac, completing the full 360° circuit in one tropical year (365.25 days).

Sun sign assignment formula: The Sun enters each sign at the vernal equinox (0° Aries, ~March 20) and moves at approximately: Degrees per day = 360° ÷ 365.25 ≈ 0.9856°/day

Each sign spans exactly 30°, so each sign governs approximately 30.44 days.

Zodiac date ranges (approximate, varying by a day either way from year to year):

• Aries: March 21 – April 19
• Taurus: April 20 – May 20
• Gemini: May 21 – June 20
• Cancer: June 21 – July 22
• Leo: July 23 – August 22
• Virgo: August 23 – September 22
• Libra: September 23 – October 22
• Scorpio: October 23 – November 21
• Sagittarius: November 22 – December 21
• Capricorn: December 22 – January 19
• Aquarius: January 20 – February 18
• Pisces: February 19 – March 20

Cusp consideration: Birthdays within ±2 days of a sign boundary are called cusp birthdays. The exact Sun entry time (available in an ephemeris) determines the correct sign, and it varies by a few hours each year due to leap years and the Earth’s elliptical orbit.

Compatibility overview (traditional Western astrology):

• Fire signs (Aries, Leo, Sagittarius): compatible with Air signs (Gemini, Libra, Aquarius)
• Earth signs (Taurus, Virgo, Capricorn): compatible with Water signs (Cancer, Scorpio, Pisces)
• Air signs: compatible with Fire signs
• Water signs: compatible with Earth signs

Chinese zodiac (for reference): The Chinese zodiac cycles through 12 animals in a 12-year repeating cycle:

• Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig
• 2024 = Year of the Dragon. Cycle repeats every 12 years.

What each variable means:

• Tropical zodiac: the Western system; based on the seasons (solstices/equinoxes), not star positions. Aries begins at the spring equinox, always.
• Sidereal zodiac: the Vedic/Hindu system; based on actual star positions. Currently about 23° behind the tropical zodiac due to precession of the equinoxes.
• Ascendant (rising sign): requires exact birth time and location; changes every ~2 hours as Earth rotates

Worked example: Birthday: July 4th. Cancer runs June 21 to July 22, so the 4th sits comfortably inside it, well clear of the Leo boundary on the 23rd.

Element: Water. Quality: Cardinal. Ruling planet: Moon. Compatible with: Scorpio, Pisces (Water), Taurus, Virgo, Capricorn (Earth).

The boundary days are where these calculators go wrong, and this one used to. March 20 and July 22 are the last days of Pisces and Cancer respectively, not the first days of Aries and Leo. Off-by-one errors at those two dates are common enough that it is worth checking any zodiac tool against them.