When to Take a Pregnancy Test

The Science Behind hCG Detection

Pregnancy tests detect human chorionic gonadotropin (hCG), a hormone your body starts producing after a fertilized egg implants in the uterine lining. Implantation typically happens 6–12 days after ovulation, with most implantation occurring around 8–10 days post-ovulation (DPO).

After implantation, hCG levels roughly double every 48–72 hours in early pregnancy. The most sensitive home tests can detect hCG at 6.3 mIU/mL — but most women won't reach detectable levels until 10–12 DPO at the earliest.

Why Testing Too Early Gives False Negatives

Even if you're pregnant, a test taken at 8 DPO will likely be negative because hCG hasn't had time to build up. This is a false negative — the pregnancy is real, but the hormone levels are too low to detect. About 50% of pregnant women will still test negative at 10 DPO.

The most reliable results come from testing on the day of your expected period or later. At that point, hCG levels are high enough for virtually any test to detect.

Tips for the Most Accurate Results

• Use first morning urine (FMU) — it's the most concentrated, giving the highest hCG reading
• Don't drink excessive fluids before testing — diluted urine can cause false negatives
• Wait the full time specified in the test instructions before reading results (usually 3–5 minutes)
• If negative, retest in 48 hours — hCG doubles every 2–3 days, so retesting gives the hormone time to rise

What About Evaporation Lines?

An "evap line" can appear on a test read after the recommended window (usually after 10 minutes). It's caused by urine drying, not hCG. Always read results within the timeframe on the box. If you see a faint line within the time window, that's likely a true positive — any line is a line, no matter how faint.