When to take a pregnancy test, and what hCG levels mean
Take a home pregnancy test from the first day of your missed period, ideally with the first pee of the morning. Tests detect hCG, a hormone your body makes once a fertilised egg implants. Testing earlier can give a false negative. A faint test line usually means you're pregnant. If the test is negative but your period still hasn't come, test again in 3 days.
Key facts
| Best time to test | First day of a missed period or later |
|---|---|
| hCG starts | After implantation, 6 to 12 days after ovulation |
| Early hCG | Roughly doubles every 2 to 3 days |
| Faint line | Usually positive |
| Common mistake | Testing too early |
How pregnancy tests work
Once a fertilised egg implants in the womb, the developing placenta makes human chorionic gonadotropin (hCG). It shows up in blood first, then in urine. Home tests contain antibodies that change colour when hCG is present.
When to take the test
- Best: on or after the first day of your missed period. Most tests are very accurate from this point.
- "Early" tests can pick up hCG a few days before your period, but a negative this early doesn't rule out pregnancy.
- Irregular cycles: test 21 days after unprotected sex.
- Time of day: morning urine is most concentrated, which matters most in the first days.
Reading your result
- Two lines, even faint: you're very likely pregnant. Read it within the time on the packet.
- One line (control only): negative. Test again in 3 days if your period doesn't come.
- No control line: the test didn't work. Use another.
- Evaporation line: a colourless line that appears after the reading time. Ignore results read late.
- Digital tests show words, which removes guesswork but can be slightly less sensitive.
hCG levels week by week
Doctors measure hCG in a blood test in milli-international units per millilitre (mIU/mL). The normal range is very wide, so one number tells you little. In early pregnancy, doctors look at whether it roughly doubles over 48 to 72 hours.
| Weeks since last period | Typical hCG range (mIU/mL) |
|---|---|
| 3 weeks | 5 – 50 |
| 4 weeks | 5 – 426 |
| 5 weeks | 18 – 7,340 |
| 6 weeks | 1,080 – 56,500 |
| 7 – 8 weeks | 7,650 – 229,000 |
| 9 – 12 weeks | 25,700 – 288,000 |
| 13 – 16 weeks | 13,300 – 254,000 |
| 17 – 24 weeks | 4,060 – 165,400 |
Under 5 mIU/mL is generally negative; over 25 is generally positive. hCG peaks around 8 to 11 weeks, then falls and levels off.
Why a test can be wrong
False negatives are common and happen when you test too early, drink a lot before testing, or read the result too soon. False positives are rare. They can follow a very early miscarriage (chemical pregnancy), fertility injections containing hCG, or rare medical conditions. Antibiotics and the contraceptive pill don't affect results.
After a positive test
Congratulations. Work out your due date with the calculator, start folic acid, and book your first appointment. Read early signs of pregnancy and the first trimester guide for what comes next.
Frequently asked questions
Can I take a pregnancy test at night?
Does a darker line mean twins?
How soon will a blood test show pregnancy?
Sources
- NHS: Doing a pregnancy test
- American Pregnancy Association: hCG levels
- ACOG: Pregnancy tests
General information, not medical advice. Medical disclaimer · How we review content
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