If you miss a period — whether you forgot your pill or are hoping to conceive — it might be an idea to take a pregnancy test. Tests can often show if you are pregnant from the first day of a missed period.

Some pregnancy tests can detect pregnancy before a period is due, but the body needs time to increase its levels of the hormone human chorionic gonadotropin (HCG) for a reliable result. Testing before a missed period can increase the risk of a false negative result.

In this article, find out how pregnancy tests work and how soon you can take one if you think you may be pregnant.

Some tests are very sensitive and can show if you are pregnant before your period is due.

However, it is best to wait until at least the first day of a missed period to take any test. For a more accurate result, take the test a week after your missed period.

The reason you shouldn’t take a test too soon is that pregnancy tests work by measuring levels of HCG, a hormone that is only present if you’re pregnant.

The body only releases HCG if a fertilized egg attaches to the uterus in a process known as implantation. Implantation usually happens around 10 days after conception, when the sperm fertilizes the egg.

Traces of HCG are present from 6 days after ovulation, but it typically takes 7–10 days after ovulatation for the body to build up enough HCG to show up on a test.

If you have an irregular cycle and don’t know when your period was due, it’s best to take the test at least 21 days after having unprotected sex.

You may receive an inaccurate result if you take the test too early in your cycle.

Whether you are trying to conceive or are concerned that your birth control went wrong, a pregnancy test can help confirm if you are pregnant or not. But, taking it too soon might give a false result.

OTC pregnancy tests typically test your urine for HCG hormone.

How you test your urine will depend on the kit you choose.

You may have to:

  • collect your urine in a cup and dip a testing stick into the liquid
  • collect your urine in a cup and use an eyedropper to move a small amount of fluid into a special container
  • place the testing stick into the area of your expected urine stream so that it will catch your urine midstream

According to the Office on Women’s Health, home pregnancy tests are almost 99% effective if you use them correctly.

You can do the test in the privacy of your own home. Simply open the test, follow the instructions, and wait for the recommended time to view the results.

After the recommended waiting time has passed, the tests will display your results in one of the following ways:

  • a change in color
  • a line
  • a symbol, such as plus or minus
  • the words “pregnant” or “not pregnant”

Most tests will give a result within a few minutes.

Here are some signs that you should take a pregnancy test.

1. You’ve missed your period

One of the first and most reliable signs of pregnancy is a missed period.

If you don’t track your cycle closely, it might be hard to determine whether or not you’re late. A 28-day menstrual cycle is typical, but cycles can vary from 24–38 days. Consider taking a test if it’s been more than a month since your last period.

Remember that other factors, besides pregnancy, can delay a period or cause you to miss one. They include stress, some medications or medical conditions, changes in birth control, and so on.

It’s also common to experience light bleeding or spotting in the early weeks of pregnancy as the egg buries deeper into the uterine lining during implantation. This may resemble a light period but does not follow the usual pattern or timing. Take note of any difference in the color, texture, or amount of blood, and seek medical advice if you have any concerns.

Always speak with a doctor if you have bleeding and a positive pregnancy test.

2. You have cramps

Implantation can produce a feeling similar to menstrual cramps. In early pregnancy, you may feel this discomfort and think your period is just around the corner, but then it never comes.

If this happens, consider taking a test.

3. Your breasts hurt

As pregnancy progresses, your body will produce more and more estrogen and progesterone. These hormones will start to make changes in your body to support the baby’s growth.

Your breasts may feel tender and appear bigger due to increased blood flow. Your nipples might hurt, and the veins might look darker under the skin.

This is also common in the days leading up to a period, so it won’t necessarily mean you are pregnant.

4. You’re feeling different

Along with cramps and sore breasts, early pregnancy can cause:

As the weeks go on, these symptoms may get stronger before your HCG levels even out late in the first trimester. You know yourself, so pay attention to your body. Any unusual changes could prompt you to take a pregnancy test.

5. Your birth control method failed

Birth control pills, condoms, and other methods don’t provide 100% protection from pregnancy. There’s always a slight chance of pregnancy, no matter how careful you are.

Birth control pills, for instance, can be over 99% effective if you always use them correctly. But, perfect use is not always possible. Realistically, they are around 91% effective.

Similarly, condoms can break and tear. Male condoms can be 98% effective with perfect use, but they are, in fact, only 82% effective with typical use.

Long-term methods, such as an intrauterine device (IUD), are more reliable and still reversible.

Even if you are using birth control, it is worth having a pregnancy test if you have other signs that could indicate pregnancy.

How accurate are at-home pregnancy tests?

At-home pregnancy tests are typically 99% accurate, as long as you follow the instructions and don’t test too soon.

How soon will a pregnancy test read positive?

Some test producers say their test can show if you are pregnant 6 days before your period is due, but these tests are less likely to be accurate. They may show you are not pregnant when in fact you are, because HCG levels are still too low.

Can pregnancy be detected after 5 days or 2 weeks?

Taking a test 5 days or even 2 weeks after having unprotected sex may not be worthwhile, as the result may be inaccurate.

What are some early signs of pregnancy?

Some early signs of pregnancy include a missed period, unusual spotting or bleeding that doesn’t follow the pattern of menstruation, sore breasts, cramps, and “just feeling different.” For many people, a missed period is the only sign they notice at this stage.

Signs that you might want to consider a pregnancy test include a missed period, sore breasts, or simply having sex with a male without using birth control.

For the best results, take the test after you think you’ve missed your period. Test during your first morning bathroom visit, or hold it for several hours to increase the concentration of the HCG hormone that the test measures.

Testing early helps to ensure that you get proper care for yourself and, if applicable, prenatal care for your baby. In the event of a positive result, contact your doctor as soon as possible to discuss your options and potential next steps.