Born on December 21: Zodiac Sign & Birthstone

Anyone born on December 21 is a Sagittarius. The December 21 birthstone is Turquoise and the December 21 birth flower is the Narcissus. This is a boundary date, so in some birth years it falls under Capricorn instead.

What it means to be born on December 21

A birthday on the 21st of December falls under Sagittarius. Sagittarius is a mutable fire sign ruled by Jupiter, linked in tradition to travel, philosophy and the search for meaning. The archer aiming at the horizon captures its love of freedom and far horizons. Its season closes autumn.

December 21 sits on the Capricorn and Sagittarius boundary

This date is one of the twelve changeovers in the zodiac. A tropical sign begins at the moment the sun reaches a particular point, and that moment drifts by roughly six hours a year before a leap day pulls it back. On a boundary date the crossing can therefore land on either side of the calendar day, depending on the birth year and the time zone. Charts that publish fixed dates, including ours, round it.

In practice that means a birthday on December 21 is Sagittarius in most years and Capricorn in some. Only an ephemeris for the exact birth year and time settles it. The full list of boundaries is in the cusp guide.

What weekday December 21 falls on

A common year is 365 days, which is 52 weeks plus one day, so a birthday moves forward one weekday each year and two across a leap year. Over time it visits all seven. The next time December 21 falls at a weekend is 2030, on a Saturday.

The weekday December 21 falls on over the next ten years.
Year	Weekday	Weekend?
2026	Monday	no
2027	Tuesday	no
2028	Thursday	no
2029	Friday	no
2030	Saturday	yes
2031	Sunday	yes
2032	Tuesday	no
2033	Wednesday	no
2034	Thursday	no
2035	Friday	no

Your December 21 birthstone and flower

Because December 21 sits in December, your birthstone is Turquoise, a sky blue to teal gem traditionally meaning protection, friendship and good fortune. Your birth flower is the Narcissus, which stands for hope, respect and good wishes. Together they make a natural birthday pairing for a card, gift or tattoo.

Every tradition tied to December 21

Everything the calendar assigns to December 21, in one table.
Field	Value
Zodiac sign	Sagittarius (November 22 to December 21)
Element and modality	Mutable Fire
Ruling planet	Jupiter
Lucky colors	Purple and Deep blue
Modern birthstone	Turquoise, sky blue to teal
Other recognized stones	Tanzanite (violet blue), Zircon (blue to colorless), Blue Topaz (pale to sky blue)
Birth flower	Narcissus, with Holly as secondary
Day of the year	356 of 366 and 355 of 365
On a sign boundary	yes, shared with Capricorn

Sagittarius strengths and matches

Sagittarius is often described as optimistic, adventurous and honest. In the traditional element model, Sagittarius matches most easily with Aries, Leo and Libra. Those percentages come from a published formula you can check on the method page, not from a reading.

See the full birth profile

Want the shareable card for December 21? Open the birth profile tool, pick this date, and download a card to save or share. You can also read the full December overview, or browse every date we cover.

Frequently asked questions

What zodiac sign is December 21?

Anyone born on December 21 is a Sagittarius, a mutable fire sign ruled by Jupiter. December 21 sits exactly on the boundary with Capricorn, so for some birth years the answer is Capricorn instead.

What is the birthstone for December 21?

The birthstone for December 21 is Turquoise, the December birthstone, which is sky blue to teal. December also recognizes Tanzanite, Zircon and Blue Topaz.

What is the birth flower for December 21?

The birth flower for December 21 is the Narcissus, the December birth flower, with the Holly as a secondary flower.

What day of the week does December 21 fall on?

In 2026 it falls on a Monday. Because a common year is 365 days, the weekday moves on by one each year and by two across a leap year, so it cycles through all seven over time. The table on this page lists the next ten years.

Where does December 21 fall in the year?

December 21 is day 356 of a leap year and day 355 of a common year.

Is December 21 on the cusp?

Yes. December 21 is a boundary date between Capricorn and Sagittarius. The sun does not cross the boundary at the same clock time each year, so a birthday here can belong to either sign depending on the birth year and time zone. Settling it needs an ephemeris, not a date table.

Born on December 21