Why a date, not a day
The Sun doesn't step from one sign to the next at midnight, or at any fixed hour — it crosses the boundary at one specific instant, the way a car crosses a state line at one specific mile marker rather than at the top of the hour. Astrologers call that instant an ingress: the Sun's ecliptic longitude reaches exactly 0° of the next sign, and from that second forward, the Sun is reckoned to be in the new sign. Everything before that instant, even by a minute, still belongs to the old one. This is why the dates below carry a time as well as a day: the day alone tells you which 24 hours the change falls in, but the instant is what actually decides which sign is which, right down to the people born an hour either side of it.
Why the date moves by about a day, year to year
A calendar year is 365 days, but Earth's actual trip around the Sun takes about 365.24 days — a quarter-day longer. Each ordinary year, the ingress instant drifts about six hours later against the clock; the leap day every fourth year pulls it back rather than letting the drift build up for good. Between one leap year and the next, a sign's start date can shift by a full calendar day, which is exactly the wobble you'll notice comparing this year's list with an older one. None of this is an error in either list — both are reading the same instant correctly. It's also worth remembering that the times below are in UTC: your own local date can land a day earlier or later, depending on your time zone and which side of midnight the crossing falls on for you.
What a cusp is, and why we skip cusp readings
A 'cusp' is the everyday name for the day a sign changes — if you were born on one of the dates below, you might describe yourself as born 'on the cusp.' The trouble with reading a cusp as its own blend of two signs is that it papers over the one fact that actually settles it: the exact instant. Someone born four hours before the ingress is fully the old sign; someone born four hours after is fully the new one, even though both share a birthday. Rather than treat the whole day as some blended in-between state, this page gives you the instant itself, so a cusp birthday can be resolved instead of left as a guess. If you know your birth time, the boundary stops being fuzzy at all.
Tropical vs sidereal, in two sentences
The dates here use the tropical zodiac, which starts Aries at the spring equinox and stays locked to the seasons rather than to the visible stars overhead. The sidereal zodiac instead tracks the actual constellations, which have slowly drifted out of step with the seasons over roughly two thousand years, so a sidereal calendar lands about three weeks later per sign than the tropical dates shown below. Most Western astrology, including every page and tool on this site, uses the tropical version, which is also the one built into the Sun sign dates people grew up reading in a newspaper or a magazine. Sidereal astrology isn't wrong on its own terms, since it's measuring a genuinely different reference point — it's simply a separate system, with its own dates, its own table, and its own answer to the question of when Aries begins.
How to read the dates below
Every entry below gives the sign the Sun is about to enter and the instant it gets there, in UTC. If your birth time and location, converted to UTC, falls after that instant, you were born under the new sign; before it, you're still the old one. For most birthdays this is academic, since you're comfortably inside a sign's five-week stretch either way. It only actually matters if your birthday lands within a day of one of these instants, where your local date might disagree with the UTC date by a day in either direction. If your birth date sits close to any line in this table and you want the specific year checked against your own birth time, that's exactly what a full chart works out for you.
Want the exact year checked against your own birth details? Open Birth chart above and enter your birth time and place.