Work out zodiac sign instantly with clear inputs, formula shown and shareable results.
Western zodiac signs run between fixed calendar cutoffs, most falling between the 19th and 23rd of each month. A 4 September birthday is Virgo, an Earth sign, with the cusp into Libra on 23 September. The cutoffs drift by a day between years because the tropical year is not a whole number of days.
Sign determination
compare the birth day against the cutoff date for that month
Elements
Fire, Earth, Air and Water each cover three signs
Because the Sun's entry into each sign shifts a few hours each year against the calendar, so the boundary date varies between years.
No longer. Precession has shifted the constellations by roughly one sign since the system was fixed about 2000 years ago.