Whether you are planning a gender-reveal party, picking a nursery theme, or simply burning through the "is it a boy or girl" tab on your phone, a pregnancy gender calculator turns a handful of fun facts into a playful Boy or Girl prediction. This tool combines three of the most popular folklore and observation-based methods — the Chinese lunar birth chart, the Ramzi placenta-side theory, and the nub (or skull) theory — and lets the majority vote decide.
None of these methods is scientific. Every fetus has roughly a 50% chance of being assigned male or female at birth, and these three methods are entertainment, not diagnosis. Think of the result as a conversation starter for your reveal party, not as a reason to paint the entire nursery.
For entertainment purposes only. This tool is for entertainment purposes only; it does not predict your baby's sex and has no medical basis. The only reliable ways to determine fetal sex are a professional mid-pregnancy ultrasound performed by a qualified sonographer, or prenatal genetic testing such as NIPT.
How to Use
- Enter the Mother's Lunar Age at Conception — your age in years on the Chinese lunar calendar, usually about one year older than your calendar age. The chart accepts ages from 18 to 45.
- Enter the Lunar Month of Conception — the Chinese lunar month in which conception happened, where the first lunar month of the year equals 1. If you only know the approximate calendar month, convert it with a simple lunar-month calendar before typing it in.
- Set the Placenta Side on Early Ultrasound only if you have a clear 6–9 week scan: Ramzi theory reads the side where the placenta sits on screen. Choose right, left, or leave it on not-sure.
- Set the Nub Angle only if you have an 11–13 week nub shot: flat and parallel to the spine leans girl, angled more than 30 degrees upward leans boy. Leave it on not-sure otherwise.
- Read the result card. Each method casts one Boy or Girl vote, the majority wins, and the entertainment confidence is the share of votes for the winning side.
If you leave both ultrasound fields on not-sure, only the Chinese lunar chart votes, and the confidence reads 100% for whatever the chart says — which just means "one method voted," not "this is certain."
The Three Methods, Briefly
Chinese lunar birth chart. A centuries-old table that crosses the mother's lunar age at conception (rows, 18–45) with the lunar month of conception (columns, 1–12). For example, a lunar age of 28 in lunar month 6 lands on Boy, while lunar age 25 in lunar month 3 lands on Girl. Originating in Chinese folklore and endlessly republished online, its hit rate has never been shown to beat a coin flip.
Ramzi theory. Proposed by a Canadian obstetrician in 2011, this idea holds that the side of the placenta on an early ultrasound (transvaginal or abdominal) hints at sex: right side leans boy, left side leans girl. Small, non-blinded studies reported mixed results, and the theory is not taught or used for clinical sex determination.
Nub / skull theory. Between 11 and 13 weeks, the genital tubercle — the "nub" — sits at the angle used to read sex in trained hands: above roughly 30 degrees from the spine leans boy, parallel to the spine leans girl. Studies show untrained parents guess at chance level, while experienced sonographers do better — but even they confirm sex definitively only later, around 18–20 weeks, and even then not perfectly.
Examples
Example 1 — The default setting. A mother-to-be was 28 in calendar years at conception, which rounds to lunar age 28, and conceived in lunar month 6. The Chinese lunar chart reads Boy, and both ultrasound fields are left on not-sure. The combined prediction is Boy with an entertainment confidence of 100% — in other words, one method voted.
Example 2 — Three methods agree or disagree. At lunar age 25, lunar month 3, the Chinese chart reads Girl. On her 7-week scan the placenta is clearly on the right, so Ramzi votes Boy, and her 12-week nub photo looks angled upward, so nub theory also votes Boy. The vote is 2 to 1 against the chart: the combined fun prediction is Boy with about 67% confidence. This is exactly why the tool shows all three votes instead of a single number.
Example 3 — No ultrasound data. A mother at lunar age 34, lunar month 5 with no early scan and no nub photo leaves both selectors on not-sure. The chart votes alone (Girl in this case), confidence 100%, and the takeaway note reminds her that folklore alone is about as reliable as a guess.
Example 4 — Boundary inputs. If you type a lunar age below 18 or above 45, or a conception month outside 1–12, the calculator stops and asks you to fix the input instead of returning nonsense — the chart simply does not exist outside those ranges.
FAQ
How accurate is the Chinese lunar gender chart?
In practice, about as accurate as flipping a coin. It is a folklore table, not a biological test, and no controlled study has ever shown it beats the expected 50% baseline. Thousands of parents share "it was right!" stories online, but the millions of "it was wrong!" stories rarely get posted.
What is the Ramzi theory and does it really predict gender?
Ramzi theory links the side of the placenta on a 6–9 week ultrasound to sex: right side, boy; left side, girl. It was proposed in 2011 and has not been validated as a clinical method. Most hospitals will not confirm sex from the placenta side, and neither should you.
What is nub theory (skull theory) and when can you tell?
Nub theory reads the angle of the genital tubercle on an 11–13 week ultrasound: flat and parallel to the spine suggests girl, angled above 30 degrees suggests boy. Trained sonographers can be right more often than chance, but even they usually wait for the 18–20 week anatomy scan, where external genitalia are much clearer.
Should I rely on this calculator before buying gender-specific nursery items?
No. This tool is built for fun and for gender-reveal games. Paint the nursery neutral, and wait for a dating ultrasound or a prenatal blood test (NIPT) before you spend money on a Boy-themed or Girl-themed shower.
How do I find my Chinese lunar age and conception month?
Lunar age is roughly your calendar age plus one, and it starts at 1 on the lunar New Year. For the conception month, convert your estimated conception calendar month with a lunar-month calendar. If you are off by a month or a year, the chart output flips — which is part of why it is unreliable.
Why does the result sometimes say "Toss-up"?
A Toss-up appears when the Boy and Girl votes tie, or when none of the three methods has enough information to vote (for example, chart plus one ultrasound method split the votes). It is the tool's honest way of saying "the fun evidence is split" rather than forcing a guess.
Disclaimer
This pregnancy gender calculator is for informational purposes only. It combines folklore and entertainment theories (the Chinese lunar birth chart, the Ramzi placenta-side theory, and the nub/skull theory) and is not medical advice, a diagnostic test, or a guarantee of your baby's sex. The only reliable ways to determine fetal sex are a professional mid-pregnancy ultrasound performed by a qualified sonographer or physician, or prenatal genetic testing such as NIPT or amniocentesis. Always discuss any pregnancy questions with your healthcare provider.