Zodiac sign calculator: exact, even on a cusp day

When someone asks for your zodiac sign, they mean the sign the Sun was in when you were born, which is why it is also called your Sun sign. In astrology it stands for your core: what drives you, what gives you energy and how you most like to show yourself.

The Sun takes a year to travel the whole zodiac and stays about a month in each sign. That is why most people know their sign from the horoscope page, no calculator needed. It gets interesting at the edges.

Date ranges like “March 21 to April 20” are rules of thumb. The Sun does not change sign at midnight but at a particular time of day, and that moment falls a little differently every year. If you were born close to a change, usually between the 18th and the 23rd of a month, you could be one sign or the other.

People born on a cusp still have exactly one zodiac sign, and the time decides which. We calculate the Sun’s position for the minute you were born and check the margin of your birth time. Without a time we check the whole day: if the Sun changed sign on your birthday, we show you both signs and the time of the change.

A calendar year has 365 days, but the Sun takes 365 days and almost six hours to travel the zodiac. So every change of sign comes almost six hours later each year, until a leap year pulls it a day forward again.

Then there is the time zone: the same moment can still be the 20th in New York and already the 21st in Berlin. That is why we do not rely on tables but calculate the Sun’s position for the moment and place of your birth.

From the date, time and place we first work out the exact moment of your birth in universal time, using the time zone and daylight saving time that applied at your birthplace back then. If your time falls in an hour that happened twice because the clocks went back, we ask instead of guessing.

For that moment, the Swiss Ephemeris, a library of planetary positions widely used in astrology, gives the Sun’s position in the tropical zodiac of Western astrology: Aries begins at the March equinox and each sign spans 30 degrees. We also calculate your Moon and, if you know the time, your rising sign. We do not store your details.