The earliest most at-home pregnancy tests will read positive is 10 days after conception. Some early-detection pregnancy tests may read positive as early as eight days post-conception with about 75% accuracy. However, all pregnancy tests are most accurate if you wait until after your period is late.1

Pregnancy tests detect the pregnancy hormone human chorionic gonadotrophin (hCG) in urine. Levels rise quickly in the first few weeks of pregnancy but can be too low to be detected if you test too early. This gives you what's known as a false-negative result, meaning you are pregnant but the pregnancy test says otherwise.

This article discusses early pregnancy tests and how soon a pregnancy test can show a positive. It explains how long you should wait to take a pregnancy test for the most accurate results and when you should contact your healthcare provider.

How Pregnancy Tests Work

HCG is produced by the cells surrounding the embryo about six days after fertilization. Home pregnancy tests measure the level of hCG in urine because the hormone is detectable in urine and levels quickly rise in the early weeks of pregnancy; thus, it should show up on the test if you're pregnant. The presence of hCG is a sure marker of pregnancy because it is usually only produced when someone is pregnant. (In fact, it's known as the "pregnancy hormone.")

Home pregnancy tests work by including material that can soak up urine and is treated to detect hCG. The test will only detect hCG if there's enough of it present in urine and the test is used as directed.

Early pregnancy tests are more sensitive than traditional over-the-counter pregnancy tests and can potentially detect hCG earlier on.

Neither is as accurate as standard tests that your healthcare provider can run, however. This is why any positive at-home pregnancy test must be confirmed by other tests to accurately diagnose pregnancy.

When to Take a Pregnancy Test

The best time to take a pregnancy test is after your period is late. By then, hCG levels should have increased to a detectable level and you can be more certain that you're not getting a false negative. 

To know when you should have gotten your period, it helps to know when you ovulated. Menstrual bleeding usually begins 14 days after ovulation. To track ovulation, you can use ovulation test kits or track your basal body temperature.

If you don't want to wait until after your missed period to take a test, early pregnancy tests can be used several days before a missed period. These tests are more accurate for people who conceived (got pregnant) earlier in their cycle. 

If you received an hCG trigger shot to help with fertility, it's best to wait two weeks after the shot to take a pregnancy test. The trigger shot can cause a false positive if a pregnancy test is taken before the medication has left your system.2

Taking a pregnancy test first thing in the morning gives you a better chance of getting an accurate result. Assuming you have not been waking up to drink a lot of water through the night, your urine will be more concentrated right when you wake up, which means hCG will also be more concentrated and therefore more detectable.

How to Take a Home Pregnancy Test

To use an at-home OTC pregnancy test, follow the package instructions. This usually means peeing on the end of a stick, which will check your urine for hCG. Small amounts of hCG can sometimes be detected in the urine about 10 days after conception.3

If you take a urine pregnancy test sooner than 10 days after conception, the tests might give a “false negative” result. If you take an early test and it's negative, you should continue to test if you miss a period.

For the most reliable results, wait until after the first day of your missed period to take a pregnancy test.4

Pregnancy tests should be kept at room temperature. Keep them away from direct sunlight, moisture, or excessive heat. Make sure to check the expiration date before using. Pregnancy tests that are past their expiration date should be discarded.

How Accurate Are Early Pregnancy Tests?

Pregnancy tests typically require at least 20 mIU/mL to show positive.5 Newer early results tests may be able to detect levels as low as 6 mIU/mL.6

Early Pregnancy Tests

Different brands make different claims about accuracy and when you should use them:

• First Response Early Results Pregnancy Test: 76% effective five days before your period is due and more than 99% three days before your period is due or later 7
• Clearblue Early Detection Pregnancy Test: 71% effective five days before your period is due, 98% three days before your period is due, and more than 99% two days before it's due or later8
• Clearblue Digital Pregnancy Test: 75% effective at detecting pregnancy three days before your period is due, more than 99% effective the day before your period is due or later9
• Natalist Early Pregnancy Test Strips: 99% effective two days before your period is due10
• MomMed HCG20 Pregnancy Test Strips: Manufacturer’s website says it is 99% accurate but does not clarify the timing; claims it can detect pregnancy as early as four days before your period is due11

Can Pregnancy Tests Be Wrong?

Pregnancy tests can be wrong. In one European study, seven pregnancy tests were tested for accuracy. Three of those seven tests were accurate 97.6% to 100% of the time. The other four tests had lower accuracy rates, ranging from 81.6% to 95.9%. The study did note that regulations for these tests are different in Europe than in the United States and that the results may also vary based on the user.12

It's rare to have a false positive because your body doesn't produce hCG unless you're pregnant. However, it's possible that if you lost a baby and didn't realize it, you may still have hCG in your system that can show up on a pregnancy test.

False negatives are much more common, and can happen for a range of reasons:

• A person tested too early and there wasn't enough hCG for the test to detect.
• A person didn't take the test correctly. (User errors include not waiting long enough between the last urination and the one used for the test or not waiting long enough to view the results of the test).
• The test is faulty.

When to Re-Take a Pregnancy Test

If your test is negative and your period is late and/or you are experiencing pregnancy symptoms, wait at least three days to test again. If your pregnancy test is still negative, test again in three days. This gives hCG levels a chance to reach detectable levels.

Some symptoms of early pregnancy include:

• Breast tenderness
• Mild cramps
• Very light bleeding (spotting)
• Increased urination
• Nausea
• Vomiting
• Fatigue
• Sensitivity to smells
• Nausea and vomiting (sometimes called "morning sickness" but can happen at any time of day)

What Is a False Positive Pregnancy Test?

False positive pregnancy tests are uncommon, but they can happen.13 Some of the causes of false pregnancy test results include:

• Evaporation line: If you wait too long to view the results, evaporation may cause a line that looks like a positive test result.
• Recent miscarriage or abortion: People who have experienced miscarriage or abortion continue to have detectable levels of hCG for five days or longer afterward.13
• Molar pregnancy: A molar pregnancy is a condition that causes abnormal development of placental tissue. This can also cause your hCG levels to increase, even though you are not pregnant.
• Certain medical conditions: Medical conditions that affect the pituitary glands can cause abnormal hCG levels. Some other conditions that can affect pregnancy test results include ovarian cysts, urinary tract infections, and certain cancers. 
• Medications: Some medications can also cause a false-positive pregnancy. Infertility drugs, for example, can contain synthetic hCG. Other drugs that may cause a false result include aspirin and methadone.

When to Call Your Healthcare Provider

If you have missed your period but have not tested positive using an at-home pregnancy test, wait about a week to see if you get your period. If not, test again.

Contact your healthcare provider if the tests stay negative and you still don't get a period. If you don't have a period for three or more months and you are not pregnant, it is called amenorrhea.14

If you do test positive, call your healthcare provider to schedule an appointment. Many want the first pregnancy appointment to occur at six to eight weeks gestation or two to four weeks after your missed period and/or a positive pregnancy test.

Summary

Most pregnancy tests are very accurate if you take them after you've missed a period. Early pregnancy tests may be able to detect a pregnancy as soon as 10 days after conception, but these tests are not as accurate.

Pregnancy tests check your urine for the presence of a pregnancy hormone called hCG. Make sure you follow the test's instructions. They are most accurate if you take them when you urinate for the first time in the morning. 

It is possible for a pregnancy test to be falsely negative. This often happens because the test wasn't taken correctly or it was taken too soon. If you test negative but are experiencing pregnancy symptoms, it's a good idea to wait a few days and retake the test.