Pregnancy test calculator: when to take a test
Enter the first day of your last period, or the date you had sex, to see the first day most home pregnancy tests work and the day the result is most reliable.
Testing too early is a common reason for a negative result in early pregnancy: the hormone a test looks for, hCG, needs time to rise (FDA). This calculator turns NHS and FDA guidance into dates for your cycle. It gives you dates, not an answer: it can't tell you whether you're pregnant; only a test can, and your doctor can confirm it.
How the calculator picks your test dates
Home pregnancy tests detect hCG, a hormone the body starts making after a fertilized egg attaches to the wall of the uterus. In a 28-day cycle, hCG reaches levels a urine test can detect about 12 to 15 days after ovulation, around the day your period is due (FDA). So the calculator adds your cycle length to the first day of your last period and shows that day as the first day most tests work (NHS). If your cycles vary, enter your longest cycle so the date isn't too early.
Testing that early still misses some pregnancies: on the first day of a missed period, 10 to 20 in every 100 pregnant women get a negative result, and the result is most reliable one to two weeks after the missed period (FDA). If you don't know when your period is due, test at least 21 days after the last time you had unprotected sex (NHS).
Common questions
You can take most home tests from the first day of a missed period (NHS). For the most reliable result, wait one to two weeks after it: on the first day, 10 to 20 in every 100 pregnant women still get a negative result (FDA).
If you don't know when your period is due, wait at least 21 days after the last time you had unprotected sex (NHS). Pregnancy can start several days after sex, because sperm can survive in the body for up to 5 days (ACOG), and a test only turns positive once the pregnancy has implanted and hCG has risen. If the sex was in the last 5 days and you don't want to be pregnant, emergency contraception can still prevent most pregnancies, and the sooner the better (WHO).
Some very sensitive tests can detect a pregnancy a few days before a missed period (NHS), but many pregnancies don't show up that early. A negative result before your period is due doesn't rule out pregnancy: test again on the day your period is due or later.
Wait a few days and test again. If the second test is also negative and your period still hasn't come, see a doctor (NHS).
Use your longest cycle of the last few months: the calculator counts from it so the date isn't too early. If your cycles are very irregular, you're breastfeeding or you don't have periods, count 21 days from the last time you had unprotected sex (NHS).
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The dates and health statements on this page follow these sources.
Medical Disclaimer
This tool is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or qualified health provider with any questions you may have regarding a medical condition.
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