When can you find out the baby's sex?
The earliest reliable answer comes from a NIPT blood test at about 10 weeks (over 99% accurate). Ultrasound can hint from 12–14 weeks with the nub, and gives its reliable read at the 18–20-week anatomy scan (~99%). Everything earlier — folk methods, the Chinese calendar, skull shape — is for fun, at roughly a coin flip.
The timeline at a glance
- From ~10 weeks: NIPT / cell-free DNA blood test — 99%+, the earliest reliable method.
- 12–14 weeks: nub theory on a clear side profile — a strong hint, not proof.
- 18–20 weeks: the anatomy scan — the standard reliable ultrasound answer (~99%).
- Any time: folk methods (Chinese calendar, cravings, ring test) — fun, ~50%.
- If medically indicated: CVS (~11–14 wk) or amniocentesis (~15–20 wk) are definitive but invasive, and done for genetic reasons, not curiosity.
Week by week
| When | Method | Accuracy | Reliable? |
|---|---|---|---|
| ~10 wk | NIPT (cfDNA blood test) | 99%+ | Yes — earliest reliable |
| 11–14 wk | CVS (if medically needed) | Definitive | Yes, but invasive |
| 12–14 wk | Nub theory (ultrasound) | ~70–90% ideal, less on poor scans | A hint, not proof |
| 15–20 wk | Amniocentesis (if needed) | Definitive | Yes, but invasive |
| 18–20 wk | Anatomy scan (turtle/hamburger sign) | ~99% with clear view | Yes — the standard |
| Any time | Chinese calendar, folk tales | ~50% | No — for fun |
The reliable methods
NIPT (from ~10 weeks). A simple blood draw analyses fragments of the baby's DNA in the mother's blood. Because it can detect a Y chromosome, it determines sex with over 99% accuracy — and it's usually ordered anyway to screen for chromosomal conditions. This is the true "earliest" answer.
The anatomy scan (18–20 weeks). By this point the genitals are formed, and a sonographer looks for the turtle sign (boy) or hamburger sign (girl). With a cooperative baby and a clear view, it's about 99% accurate — the standard ultrasound answer most parents rely on.
The early hints (fun, not proof)
Nub theory (12–14 weeks). The genital tubercle's angle to the spine hints at sex on a clear side profile — over 30° leans boy, parallel leans girl. Under ideal conditions it can be quite good, but image quality makes or breaks it. Start with nub theory explained or learn how to find the nub.
Ramzi theory (from ~6 weeks). Claims the placenta's side predicts sex. It's the earliest ultrasound guess, but it hasn't been reproduced in research and sits near 50% — see Ramzi theory.
Folk methods (any time). The Chinese gender calendar, cravings, morning sickness and the ring test are a fun tradition, but every one of them lands at chance. The honest rundown is on old wives' tales.
Can't wait for the anatomy scan? Try the early methods on your 12-week scan for fun — upload it and let Peek take a look.
Try the nub guesser →FAQ
Make the wait fun
While you wait for the reliable answer, BabyPeek lets you upload your early scan and runs five folk methods together for a majority verdict — the nub, Ramzi, skull, ultrasound signs and the Chinese calendar — then spins it into a shareable gender reveal.
For entertainment only. This is not medical advice — confirm your baby's sex with your doctor.