When the Pregnancy Test Positive Line Shows up Later

Woman taking pregnancy test
Zave Smith/Getty Images

You happened to take a home pregnancy test, and after waiting the allotted time for the result, you notice that the result window shows one single, negative line—that is, until you went back to the bathroom later, glance back at the used test and notice that now the positive line is showing up. What gives?

Instructions on most pregnancy tests will tell you to read the results in a certain amount of time, usually from a couple of minutes up until 10 minutes later. So you may take a pregnancy test and read it within the above time period as negative.

Evaporation Lines

If you happen to be like many women and keep the test around to look at later, you may notice that after that allotted time, the test now appears to have a positive result. This is called an evaporation line. It is not indicative of a positive pregnancy test.

Evaporation lines happen when the urine that was on the test area starts to dry out and evaporate. The chemical composition of that particular urine sample has now changed since that urine sample evaporated, sometimes causing the test to show a positive line. This evaporation line is different from a faint test line (which is a valid positive result) since more time has passed than instructed.

Faint Test Lines

If you took the test correctly and followed all of the instructions correctly, you may have noticed a thin, faint line in the test result window of your test after a few minutes of taking the test. You thought the line was too faint to count, but after 10 minutes that line got even darker, so now what? There are several reasons you might see this faint line.

  • Too early in your cycle to test: If you test earlier than 10 to 12 days past ovulation, then the hCG hormone may not be at a high enough level to produce more than a very faint line. The best time to test is after your period is late, or two weeks after you ovulated.
  • Using a lower sensitivity test: You may need a test with higher sensitivity levels so that you can have accurate results sooner.
  • Too much fluid: You can dilute your urine sample if you are urinating too frequently or drinking too many liquids—this is why first-morning urine samples are recommended for pregnancy testing.
  • Chemical pregnancy: When implantation of a fertilized egg happens, hCG is produced, even though that egg may not be viable. Sometimes a miscarriage quickly follows. This chemical pregnancy creates a faint positive line on a pregnancy test. If you had not tested at this point, you might not have known that this occurred, because the resulting miscarriage can look like a regular period.

If you are still unsure about pregnancy test results, try waiting a day or two to take another test. Use a sample from your first-morning urine (which is more likely to have higher concentrations of the pregnancy hormone, hCG).

A Word From Verywell

It can very stressful to see confusing results on your pregnancy test, such as faint lines or evaporation lines. After all, you were likely expecting a clear answer one way or the other. If you are uncertain about the results of a pregnancy test, talk to your doctor to discuss next steps, which may involve further testing to determined whether or not you are pregnant.

Was this page helpful?
Article Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. Guidance for over-the-counter (OTC) human chorionic gonadotropin (hCG) 510(k)s - Guidance for industry and FDA reviewers/staff. Updated August 20, 2018.