The method and its ceiling
Popular sign lookups work from date ranges: Capricorn from about 22 December to about 19 January, and so on round the year. The ranges are approximations of the ingress dates, which themselves move by a day or so between years. Feed a date in, get a sign out, and the method is finished.
Because it is finished, the rest of the page has to come from the sign as a whole. So a 29 December birthday is described with the same sentences as a 14 January one, and the description could not have been written differently, since nothing in the method distinguishes them. The agreement between those pages is agreement about a lookup table, not corroboration of anything.
The measurement the ranges throw away
Behind the ranges is a continuous quantity: the Sun's longitude along the ecliptic. On 29 December at noon it stands between about six point nine and eight point two degrees of Capricorn, taking every year from 1930 to 2035. The spread is small because the leap year rule keeps the calendar and the orbit close together over long periods. Every ordinary year slips the date back a fraction against the orbit, and every leap day pushes it forward again, so the residue that survives is small.
That single number does more work than the sign name. It fixes which of the three decans applies, it decides how close the Sun sits to any aspect it makes with another planet, and it can decide which house the Sun occupies once a birth time places the house cusps.
The layer nobody prints
Seven degrees of Capricorn is inside the first decan, the band from zero to ten, which the Chaldean order assigns to Jupiter. Saturn still rules the sign, so a traditional reading of this position works with both planets rather than one.
This is not obscure or contested material. It is standard technique with a long history, and it is the layer that separates a late December Capricorn from a mid January one. It goes unmentioned on nearly every birthday page because printing it requires a calculation rather than a table lookup. That is a difference in effort rather than in difficulty, and it is the whole reason the layer is missing.
What is still missing, and honestly so
Even with the degree and the decan in hand, the date has told you about one placement. The Moon changes sign every couple of days, so 29 December leaves two possibilities open and only the hour of birth chooses between them. The rising sign is wide open, since the Earth carries all twelve past the eastern horizon in a day.
A page that claimed to describe your character from this date would be overreaching in a way that the tradition itself does not. The widget above does the narrower and more useful thing: it works out your own solar longitude from your year, time and birthplace, and reports the distance from the nearest sign boundary so you can see for yourself how settled the answer is. What it will not do is tell you what kind of person you are, because no calculation from a date can.
Questions people ask about this
Is 29 December definitely Capricorn?
Yes. The Sun entered the sign at the solstice a week earlier, and no year in the modern calendar puts this date on the Sagittarius side of the boundary.
Why do all the descriptions sound the same?
Because they are drawn from the sign rather than the date. A date range method produces a sign name and nothing more specific, so the remaining text has to describe the whole thirty degree band.
What is the Sun's degree on this date?
Around seven degrees of Capricorn, ranging from about six point nine to eight point two at noon across the years from 1930 to 2035.
Which decan applies?
The first, covering zero to ten degrees of Capricorn, with Jupiter as its Chaldean ruler. The position is far enough from the ten degree line that the answer holds for every birth year.
Does a more specific answer change my sign?
No. It refines the description of a placement that was never in doubt. The sign stays Capricorn whatever the degree turns out to be.
What would tell me more than my birthday does?
A birth time and birthplace. Together they fix the Moon sign, the rising sign and the houses, and those account for most of the difference between two charts sharing a date.