Measuring the gap
Across noon positions from 1930 to 2035 the Sun on 16 March stands between about 25.0 and 26.4 degrees of Pisces. A sign holds thirty degrees, so the remaining distance to zero Aries is somewhere between roughly three and a half and five.
The Sun covers a little under a degree a day, which turns that gap into four days or so. The equinox lands around 20 March, and no year in the range brings it forward far enough to reach this date.
That is what a boundary distance is for. It converts a vague worry about being near a cusp into a number you can look at and dismiss.
Why the boundary moves at all
The Sun enters Aries the instant it reaches zero degrees of ecliptic longitude, and that instant falls at a different hour each year. It drifts about six hours later annually and jumps back roughly eighteen hours whenever February gains a day.
So printed sign dates that give a fixed day are rounding a moving moment. For dates near a boundary that rounding matters. For this one it does not, because the whole drift is a fraction of the gap.
Time zones do the same work at a smaller scale. An ingress is one global instant and only the local clock differs, so a moment that is late evening in London is afternoon in New York and the following morning in Tokyo. For a boundary birthday that decides the sign. Here it decides nothing.
The decan at this degree
Twenty six degrees sits in the third decan of Pisces, from twenty to thirty, the last of the thirty six faces before the circle restarts. The Chaldean sequence closes on Mars there and the triplicity scheme assigns the face to Scorpio, another Mars sign in the traditional scheme.
Older texts read the closing face as the most directed stretch of Pisces, with the sign's diffuseness gathered into something with an edge. That is what the tradition attaches to the band. It is not a description of anyone born inside it.
The face holds for every year and every hour of this date. Both of its edges, at twenty degrees behind and thirty ahead, are days away in solar travel, so no calculation is going to move this birthday out of the band.
The questions the date leaves open
With the sign settled and the decan settled, what remains is everything the hour controls. The Moon travels roughly thirteen degrees a day and can be in either of two signs on 16 March, sometimes with only a few hours between the two answers.
The Ascendant is faster still, turning a degree every four minutes, so any of the twelve signs can be rising and the houses move with it. The widget above computes your solar degree from your year and birthplace and gives your own distance from the nearest boundary rather than the range printed here.
House placement follows the Ascendant. The same solar degree can fall in any of the twelve houses depending on the moment of birth, and most practitioners read the house as carrying more weight than the decan does. None of that is reachable from a calendar date on its own.
Questions people ask about this
Is 16 March Pisces or Aries?
Pisces, without exception. The Sun is still several degrees short of the equinox on this date in every year covered by modern records.
How many degrees is 16 March from Aries?
Roughly three and a half to five, depending on the year, which is about four days of solar travel. The widget above gives the figure for your own birth details.
Am I on the Pisces Aries cusp?
No. That word gets used for dates where the sign genuinely depends on the year and the hour, and this is not one. The gap here is far wider than the drift that causes those cases.
Why do some sources list Pisces ending on 19 March and others on 20?
Because the boundary is an instant that falls at a different hour each year, so rounding it to a calendar day gives different answers in different years.
What decan does 16 March fall in?
The third decan of Pisces, the final one of the thirty six. Both the Chaldean order and the triplicity scheme give it to Mars.
If the sign is certain, what is left to calculate?
The degree, the decan, the Moon sign, the Ascendant and the houses. Only the first two come from the date, and the rest need the hour and the birthplace.