When Can You Find Out the Sex of Your Baby? All Methods by Week

Here is every method for finding out your baby's sex, arranged by the earliest week it can be used, with accuracy and evidence for each:

The honest hierarchy is clear: NIPT and the 20-week scan are the gold standards; nub theory is the best early ultrasound method; everything else is fun but not reliable.

Not reliably. Before 10 weeks, the options are limited:

• SneakPeek claims to work from 6 weeks, but the fetal DNA fraction is very low this early, increasing the risk of inconclusive or incorrect results. Real-world accuracy is likely lower than the claimed 99%, and contamination can cause false boy results. See our SneakPeek guide.
• Ramzi theory claims to work from 6 weeks by reading placenta side, but it has never been replicated and performs at chance. See our Ramzi theory guide.
• Old wives' tales and the Chinese gender predictor can be used at any time but perform at chance (~50%).

The honest answer: if you want a reliable answer before 10 weeks, there is not one. Patience — or NIPT from 10 weeks — is the evidence-based path.

NIPT (non-invasive prenatal testing) is the earliest reliable method. It is a maternal blood test that analyses cell-free fetal DNA in the mother's blood. If Y-chromosome DNA is detected, the baby is male; if it is absent, the baby is female.

NIPT is approximately 96–99% accurate for sex determination (Devaney et al., JAMA 2011), making it the gold standard for early sex prediction. It is primarily a chromosomal screening test (for conditions like trisomy 21), with sex as a by-product.

Private NIPT in the UK typically costs £200–£500 and results take 5–10 working days. It requires a venous blood draw at a clinic. For the full details, see our NIPT guide and our NIPT vs nub theory comparison.

Nub theory becomes reliably useful from about 12 weeks. It reads the angle of the genital tubercle (the "nub") on a mid-sagittal (side-on) ultrasound image. If the nub is angled more than 30° upward, it suggests a boy; if it lies flat and parallel, it suggests a girl (the 30-degree rule from Efrat et al., 1999).

Real-world accuracy at 12–13 weeks is about 85–90% with a clear image (Manzanares et al., 2016), rising above 95% as the baby grows. At 11 weeks it is only about 70% — see our guide to nub theory at 11 weeks. At 13 weeks it peaks above 90% — see our guide to nub theory at 13 weeks.

The advantage of nub theory is that it uses the 12-week scan you are already having — no extra appointment, no blood draw, no lab wait. NubHub reads the nub on your scan with AI plus a human double-check, delivering a result in about 2 hours for under £40, with a money-back guarantee. See how our AI works.

The 20-week anatomy scan (also called the anomaly scan or mid-pregnancy scan) is the clinical standard for sex determination. By 18–20 weeks, the external genitals are fully developed and visible on the ultrasound, so the sonographer can usually see the sex directly rather than inferring it from the nub angle.

Accuracy is approximately 95–99%, depending on the baby's position and image quality. If the baby is in a good position and the sonographer gets a clear view, the result is very reliable. If the baby is shy (legs crossed, face-down), the sonographer may not be able to tell, and you may need to wait or try again.

This is the scan most parents in the UK rely on for the "official" answer. It is available on the NHS as part of routine antenatal care. For what to expect, see our guide to telling gender at 12 weeks, which also covers the 20-week confirmation.

The right method depends on when you want to know, how much certainty you need, and your budget:

• You want the earliest reliable answer: NIPT from about 10 weeks (~96–99%, ~£200–500, results in 5–10 days).
• You want a quick, low-cost early glimpse: nub theory on your 12-week scan (~85–90%, under £40 with NubHub, results in ~2 hours). See our guide to nub theory.
• You want near-certainty at no extra cost: the 20-week anatomy scan (~95–99%, free on the NHS).
• You want an at-home test before any scan: SneakPeek from 6 weeks (claimed ~99%, ~£60–100, contamination risk). See our SneakPeek guide.
• You want to keep it a surprise: go team green and find out at birth. See our team green guide.

Many parents combine methods: a nub theory reading at 12 weeks for the early excitement, NIPT for a more accurate early confirmation, and the 20-week scan as the final answer. When methods agree, you can feel very confident. For more on the emotional side of finding out, see our guide on gender disappointment.

Whatever you choose, remember that no method is truly 100% — but NIPT and the 20-week scan come close. Nub theory is a fun, evidence-backed early glimpse, not a diagnosis. For common questions, see our FAQ, and for the science behind our readings, see how our AI works.