Medical disclaimer. This article is for entertainment and general information. Zodiac signs have no medical, developmental, or predictive meaning, and nothing here replaces advice from your midwife or doctor. Your due date and everything scheduled around it should come from your provider.
Working out your baby zodiac sign by due date takes one lookup: find your estimated due date in the 12-sign calendar below and read across. A 10 July due date gives you a Cancer baby; 25 October gives you a Scorpio. That is the whole method, and it is the same one our baby zodiac predictor runs.
The interesting part is what happens next. Due dates move, and babies arrive early, late, and occasionally on a completely different sign than the one you spent five months telling people about.
The 12 date ranges
These are the exact boundaries the calculator uses, alongside the standard element grouping for each sign. They are the usual Western sign dates, and they do not shift year to year.
| Sign | Date range | Element |
|---|---|---|
| Aries | 21 Mar – 19 Apr | Fire |
| Taurus | 20 Apr – 20 May | Earth |
| Gemini | 21 May – 20 Jun | Air |
| Cancer | 21 Jun – 22 Jul | Water |
| Leo | 23 Jul – 22 Aug | Fire |
| Virgo | 23 Aug – 22 Sep | Earth |
| Libra | 23 Sep – 22 Oct | Air |
| Scorpio | 23 Oct – 21 Nov | Water |
| Sagittarius | 22 Nov – 21 Dec | Fire |
| Capricorn | 22 Dec – 19 Jan | Earth |
| Aquarius | 20 Jan – 18 Feb | Air |
| Pisces | 19 Feb – 20 Mar | Water |
A few boundary details worth knowing. Leap day, 29 February, sits inside the Pisces range. Capricorn is the one sign that crosses the new year, so a late-December and a mid-January due date give you the same answer. And no sign lines up with a calendar month: each range runs somewhere between 29 and 32 days and starts near the 20th rather than the 1st.
Cusp dates: when two signs are still in play
The last day of one sign and the first day of the next are usually called the cusp. There are 12 of them, and they cluster around the 19th to the 23rd of every month.
A calculator cannot sit on the fence — feed it 22 July and it returns Cancer, feed it 23 July and it returns Leo. But if your due date sits in that neighbourhood, treating the answer as settled is optimistic: births scatter on both sides of the estimate, and the scatter is far wider than the few days between a due date and the nearest boundary.
If your due date falls within about a week of a cusp, it is fair to say your baby is "probably one of these two."
Why the sign can shift: the due date is an estimate
An estimated due date is a midpoint, not an appointment. The NHS treats anything from 37 to 42 weeks from your last period as a normal pregnancy — a five-week window. A 2013 study of naturally conceived pregnancies, where ovulation was pinned down by hormone measurements rather than guessed, found the median time from ovulation to birth was 268 days and that gestational length still varied by 37 days across the group, even with preterm births excluded.
Spread births across a window that wide and the odds of landing on any one named day are low. Here is a well-sourced slice of that spread: in US final data for 2024, 10.41% of babies were born preterm — before 37 weeks. Every one of those birthdays falls earlier than the due date, and some of them fall in the previous sign.
Then there is the dating itself. Your first due date usually comes from your last menstrual period; MedlinePlus advises a first-trimester ultrasound "to get an idea of your due date," and the NHS says the 12-week scan "can more accurately estimate how many weeks pregnant you are." So the date can move before anyone goes into labour — and since each sign spans about 30 days, a revision of a few days is enough to flip the answer whenever the due date sits near a boundary.
None of that is a reason to skip the fun. It is a reason to hold it loosely. For the arithmetic behind the date itself, we wrote up how due date calculators work separately.
Starting from a conception date instead
If you tracked ovulation and know roughly when you conceived, you can go the other way. Our calculator adds 266 days — 38 weeks — to the conception date to produce an estimated due date, then reads the sign off that. It is the same 266-day offset the ProbaBaby app uses, so the two agree.
That path carries the same uncertainty as any other due-date estimate, plus whatever imprecision is in the conception date itself. It is most useful before a dating scan, as a first guess.
A note on the astronomy
Sign dates are a calendar convention, not a measurement of where the Sun actually is. The modern Western zodiac was defined about 2,000 years ago, and the slow wobble of Earth's axis has shifted the sky since: astronomers put signs and constellations about one calendar month apart today, and count 13 constellations along the Sun's path, not 12.
So a "Leo" baby born in early August is not, to an astronomer, born under Leo at all. Worth knowing, not worth losing sleep over.
How ProbaBaby helps
The ProbaBaby app ships this as the Baby Zodiac Predictor. You pick either a due date or a conception date; in conception mode it adds the same 266 days before reading the sign, and the date picker opens six months out by default. The result screen shows the sign, its date range formatted in whatever language the app is set to, and its element — fire, earth, air, or water — with a one-line trait description. A companion tool in the app, Baby Zodiac Profile, goes further: a ruling planet, three positive traits and two challenges, four compatible signs, two lucky colours and two lucky numbers, and a parenting tip for the sign. The label the app puts on the tool is blunt: "Zodiac predictions are for entertainment purposes only and should not be taken as factual."
If you enjoy this sort of thing, the Chinese gender predictor sits in the same entertainment-only bracket. The disclaimer the app attaches to that one puts a number on it: "The actual accuracy is approximately 50% - the same as random chance."