Why the pages all match
Almost every birthday page in existence is generated from a table of sign date ranges, twelve rows of start and end dates, joined to a paragraph of sign description. Feed in 16 January and the table returns Capricorn, and the paragraph is the same one served to everyone born across a full month.
Nothing in that process ever calculates a position. It cannot report a degree, it cannot report a decan, and it has no way to say how close to a boundary any particular birthday falls. That is why the pages are interchangeable, not because the subject is thin.
What a calculated position adds
On 16 January the Sun has been between about 25.2 and 26.6 degrees of Capricorn at noon in every year from 1930 to 2035. That is a spread of well under a degree and a half over more than a century, held in place by the leap year cycle keeping the calendar in step with the orbit.
From that figure the decan follows without ambiguity. Twenty six degrees is in the third band of the sign, twenty to thirty, which the Chaldean order gives to the Sun while Saturn keeps the sign entire. Tradition reads that combination as Saturn's patience aimed at something that will eventually be seen, though that reading is inherited interpretation rather than a measurement.
The same calculation also gives Mercury and Venus a boundary. Neither wanders far from the Sun, so on this date Mercury is generally within about a sign of Capricorn and Venus within two, which is a real constraint even though it falls well short of an answer.
The distance to the boundary
The Sun leaves Capricorn at thirty degrees, so this birthday sits three to five degrees short of the edge, which is three to five days of solar motion. That margin is far too wide for the hour of birth or the time zone to matter.
It is a genuinely useful thing to know. On dates within a degree of a boundary, an unknown birth time leaves the sign itself unsettled. On this one the answer holds no matter what your records say about the hour, and the widget above will show you the margin as a number.
What still cannot be looked up
The Moon changes sign every two and a half days, so on any 16 January it may be in one of two or three signs depending on the year and hour. The ascendant runs through all twelve in a day and answers to the clock and the latitude of the birthplace rather than the date.
Those are the placements that separate two people who share this birthday. The Sun is what they have in common with a twelfth of the population, and it is the only piece a date driven page was ever able to give them.
None of that is a criticism of the sign description itself. Capricorn as cardinal earth under Saturn is a coherent piece of tradition and worth reading. The problem is only that it is served as though it were an answer about a person, when it is an answer about a month.
Questions people ask about this
What sign is 16 January?
Capricorn in every year, with several days of margin on both sides. No plausible birth time or time zone puts it in another sign.
What is the Sun's degree on 16 January?
Around twenty five to twenty seven degrees of Capricorn, set precisely by your year and hour. The widget above computes it and reports the distance to the sign boundary.
Which decan is this birthday in?
The third decan of Capricorn, twenty to thirty degrees, assigned to the Sun in the Chaldean order. Saturn rules the sign throughout regardless of the decan.
Why does every site say the same thing about this date?
Because they all read a sign from a date table and then print a generic sign description. Nothing in that method computes a position, so nothing more specific can come out of it.
Am I anywhere near a cusp?
No. The sign changes at thirty degrees of Capricorn and this birthday sits several degrees short of that, which is several days of the Sun's motion.
What should I look up next?
The Moon and the ascendant, since those are the placements a date cannot supply and the ones that differ between people who share your birthday.