19 February to 20 March
Pisces runs from three hundred and thirty degrees of ecliptic longitude to three hundred and sixty, and that upper figure is also zero: the March equinox, where the zodiac closes and the count begins again. No other season ends at the origin of the coordinate system.
The opening crossing falls on 18 or 19 February and the closing one on 19 or 20 March. Each moves within a window of about a day and a half over the leap cycle, because the calendar approximates a tropical year in whole days and corrects itself every fourth February.
The last sign, and Venus at twenty seven degrees
Mutable water closes the wheel, and Jupiter rules the sign as it rules Sagittarius. Venus is exalted at twenty seven degrees of Pisces, which places the exaltation in the final days of the season, within about seventy two hours of the equinox in most years.
Through the month the Sun climbs towards the celestial equator and the northern days lengthen fastest of the whole year. The decans belong to Saturn, Jupiter and Mars, so the season ends under the most forceful of the classical rulers rather than the softest.
Sidereal Pisces sits three weeks later
The zodiac used in India is fastened to the stars, the Western one to the equinox, and the equinox has been drifting backwards against the stars at about one degree every seventy two years. The accumulated separation is now roughly twenty four degrees.
Sidereal Pisces therefore covers approximately the middle of March to the middle of April, and a tropical Pisces Sun in the sign's first twenty four degrees is a sidereal Aquarius Sun. The systems measure from different origins and are not competing estimates of one quantity.
The limits of the range itself
Within a couple of days of either edge, published ranges disagree with each other often enough that the same birthday appears under two signs in different books. Only the year, the recorded time and the place resolve it, and the resolution is exact: the Sun is short of a multiple of thirty degrees or past it.
Nothing else in a chart follows from a date. The Moon covers roughly half a sign in a day and the Ascendant depends on the hour and the latitude, so both need more information than a birthday supplies.
Questions people ask about this
What are the Pisces dates?
Approximately 19 February to 20 March. The exact start falls on 18 or 19 February and the end on 19 or 20 March, varying with the year and with the time zone the birth is dated in.
Why do the dates change from year to year?
Because the tropical year is not a whole number of days. The ingress slips about six hours later each year and is pulled back by each leap day, so it oscillates across roughly a day and a half.
When is Pisces season this year?
Within the range above, at a minute that has to be calculated for the specific year. Anyone born close to either edge needs the actual solar position rather than a table.
Why does Vedic astrology not make me Pisces?
It measures from the fixed stars rather than from the equinox, and the two references have separated by about twenty four degrees. That moves every sidereal boundary later by a little over three weeks.
Does being born on the first day of Pisces mean anything special?
It puts the Sun in the first degree of the sign, which matters for aspects and house placement. The tradition does not read it as a weaker or stronger version of the sign itself.