The best time to take a pregnancy test is on the day your period is due or later. Testing at this point gives most home pregnancy tests enough time to detect the hormone produced during pregnancy, called hCG. Testing earlier is possible with some products, but accuracy drops significantly the further ahead of your missed period you test.
How Your Body Sets the Timeline
After a fertilized egg implants in the uterine wall, your body begins producing hCG. This hormone first becomes detectable in blood and urine between 6 and 14 days after fertilization. That wide range exists because implantation itself doesn’t happen on a fixed schedule. It can occur anywhere from 6 to 12 days after ovulation, and hCG production ramps up gradually from there.
In the earliest days after implantation, hCG levels are extremely low. They roughly double every 48 to 72 hours in a healthy pregnancy, which is why waiting even a day or two can make the difference between a faint line and a clear positive. By the time your period is due (roughly 14 days after ovulation), hCG levels have typically climbed high enough for a standard home test to pick up.
Early Detection Tests vs. Standard Tests
Home pregnancy tests vary in how sensitive they are. Sensitivity is measured by the lowest concentration of hCG the test can detect. Standard tests typically require 25 mIU/mL of hCG in your urine. Early detection tests claim sensitivities as low as 10 or 12 mIU/mL, which means they can sometimes pick up a pregnancy a few days before your missed period.
That said, testing early comes with a tradeoff. Your hCG level may be hovering right at the detection threshold, giving you a faint result that’s hard to interpret or a false negative because the hormone simply hasn’t built up enough yet. If you test before your missed period and get a negative result, it doesn’t necessarily mean you’re not pregnant. It may just mean it’s too early.
Timing for Irregular Periods
If your cycle length varies from month to month, figuring out when your period is “late” gets tricky. The Office on Women’s Health recommends counting 36 days from the start of your last menstrual period, or waiting four weeks after the sex that may have led to pregnancy. By that point, hCG levels in a viable pregnancy should be high enough for a reliable result.
If you test at that point and get a negative but still suspect you’re pregnant, wait a few more days and retest. A blood test from your doctor can also detect hCG at lower concentrations than a home urine test, making it a useful next step when your cycle makes timing uncertain.
Time of Day Matters
First morning urine gives you the best shot at an accurate result, especially in the early days of pregnancy. Your urine concentrates overnight while you sleep, which means the hCG level per milliliter is at its highest when you first wake up. Testing later in the day, particularly if you’ve been drinking lots of water, dilutes your urine and can push hCG below the test’s detection threshold.
If you can’t test first thing in the morning, try to wait at least three hours since your last trip to the bathroom before taking the test. Avoid drinking large amounts of fluid in the hours beforehand.
What Can Cause a False Positive
False positives on home pregnancy tests are uncommon, but they do happen. The most straightforward cause is fertility medications that contain hCG itself. If you’re undergoing fertility treatment and have received an hCG injection to trigger ovulation, that synthetic hormone can linger in your system and register on a test for up to two weeks after the shot.
A handful of other medications can also interfere with results. Certain antipsychotic medications, some anti-seizure drugs, specific anti-nausea medications, and progestin-only birth control pills have all been associated with false positives. If you’re taking any of these and get an unexpected positive, a blood test can confirm whether you’re actually pregnant.
Chemical pregnancies are another source of confusing results. These occur when a fertilized egg implants briefly and produces enough hCG to trigger a positive test, but the pregnancy doesn’t continue. You might get a positive result followed by your period arriving a few days later. This is technically a true positive (hCG was present) rather than a test error, but the outcome feels like a false alarm.
What a Faint Line Means
Any visible line in the result window counts as a positive, even if it’s barely there. A faint line typically means hCG is present but at low levels, which is common when testing very early. If you see a faint line, test again in two to three days. In a progressing pregnancy, the line should darken noticeably as hCG continues to rise.
One important distinction: read your result within the time window specified in the instructions, usually between 3 and 10 minutes. Lines that appear after the window closes (sometimes called evaporation lines) can look like faint positives but aren’t reliable. Check the result on time, then set the test aside.
If Your First Test Is Negative
A negative result when your period is late doesn’t always rule out pregnancy. You may have ovulated later than usual that cycle, which shifts the entire timeline. If your period still hasn’t arrived after a few more days, retest. Most pregnancies will produce a clear positive by one week after a missed period, regardless of cycle length or ovulation timing.