Since the beginning of time, no matter who you are or where you’re from, if you think you’re pregnant, you really want to know. Right now.

Thankfully, we have at-home pregnancy tests. But while the boxes at the drugstore promise to tell you right now if you’re pregnant or not, remember: These things aren’t magic. They work by detecting the pregnancy hormone human chorionic gonadotropin (hCG), and—while these tests are quite sensitive—it takes time after conception for your body to produce a high enough level of hCG to get a positive result.

Urine LH Ovulation Test Midstream

How does a pregnancy test work?

HCG is a hormone that your body begins to produce after an embryo implants in your uterine lining. Pregnancy tests can be performed either by urine testing at home, which is the most common, or blood tests that are done in a doctor’s office or lab.

In most at-home pregnancy tests, there is a wand that is either held under the urine stream or placed into a urine sample for a specified period of time. Then you wait for a result, which can take about three to five minutes, depending on the test.

Different tests have different ways of displaying results. Some have digital readouts that say “pregnant” or “not pregnant.” Others use lines or a plus or minus to show the result. With lines, you’ll always want to see the control line—this shows that the test worked. Then, if a second line appears, that indicates a positive result.

Over the years, tests have become increasingly sensitive. Today, some can detect 10 milli-international units (mIU) of hCG per milliliter (mL) of urine, although most pregnancy tests detect at 25mIU/ml. The more sensitive tests might catch a pregnancy a day or so before other tests, but after those first days, there is no advantage to the higher sensitivity, since levels of hCG double approximately every 48 hours in early pregnancy.

When should you take a pregnancy test?

You can take a pregnancy test whenever you want to, but it may be pointless if you take it too early. You’ll get the most accurate result if you wait until at least the first day of your missed period. By then, most at-home pregnancy tests give nearly 100 percent accurate results.

The earliest a test could pick up hCG would be eight days after ovulation, or five days before an expected period—although for many people, this is too early to detect hCG, and it is recommended to wait until the day of a missed period for more accurate results. The time between ovulation and the start of a period is called the luteal phase, and it lasts 14 days. It takes at least six days from ovulation to implantation (and can take up to 12), and it takes at least another two days for hCG levels to rise to detectable levels in the urine. However, even if you take an early pregnancy test five days before you are expecting to get your period, you could still get a false negative if you ovulated later than expected, implantation took longer than six days, or hCG levels were simply not detectable enough.

What’s the best time of day to take a pregnancy test?

For best results, manufacturers recommend taking a pregnancy test first thing in the morning. That is when the hCG in your urine will be most concentrated. Later in the day, after you have started eating and drinking, especially in the first few days of pregnancy, hCG levels could be so diluted that the test won’t detect them.

How accurate are pregnancy test results?

On the day of the missed period, pregnancy tests are quite accurate. A 2022 meta-analysis  found that, “the current generation of tests has close to 100 percent sensitivity and specificity in detecting hCG at concentrations of 25mIU/mL or more.” If you get a positive pregnancy test, let your OB-GYN know and they'll give you next steps. They'll likely want to see you between week 6 and 8 of pregnancy (the week of your missed period tends to be week 4). Of course, if you're worried and want to see your doctor sooner for confirmation of your pregnancy, you're well within your right to ask for that.

What causes false negatives?

A false negative pregnancy test is most often caused by taking the test too early. Even though it is possible for some tests to detect pregnancy five days before a missed period, in the case for many pregnancies, hCG levels simply haven’t gotten high enough, either because ovulation or implantation occurred later, or because your body hasn’t produced enough hCG yet. When a test says it is 99.9 percent reliable, it refers to the first day of a missed period, not five days earlier.

If you ovulated later in your menstrual cycle than anticipated, it’s possible to get a false negative, because implantation may have occurred later than you calculated.

Drinking too much water before a pregnancy test can also cause a false negative, because the level of hCG in the urine will be diluted. (And don’t even get us started on “line tweaking” and all the ways people try to detect a faint line. Truly, save yourself a lot of emotional pain by trying as hard as you can to wait until that day of your missed period.)

Can you get a false positive?

False positive pregnancy tests are very rarely a thing. One of the most common reasons for a false positive is a chemical pregnancy, or another type of non-viable pregnancy. Because implantation has occurred, hCG levels rise during chemical, molar, and ectopic pregnancies. In these cases, the test is accurately detecting hCG, but the pregnancy is not viable.

Medication can also cause false positive results. This could be due to fertility treatments that use medications containing hCG-containing drugs, such as IVF. Rarely, cancer, cancer treatments and medications can also cause false positives pregnancy tests. If you’re on medication and you’re trying to conceive, ask your doctor if it could have an impact. (Or a Conceive coach can help, too.)

What about blood tests?

Your doctor can also test for pregnancy with a blood test, which can detect a smaller amount of hCG. A blood test is more sensitive than a urine test—usually detecting a pregnancy around six to eight days after ovulation. You can request a blood test from your doctor if you have an infertility diagnosis or are working with an REI as you try to get pregnant and insurance will likely cover it. (Our Conceive fertility insurance experts are on hand if you have any questions.)

How to choose a pregnancy test

At-home pregnancy tests basically all work the same way, and, with very few exceptions, have the same level of sensitivity. That said, they are not all manufactured to the same standard, nor are they all priced the same or equally easy to read. Scroll through any TTC group and you will see discussions about blue line and pink line tests, bulk orders from Amazon, and the ease of digital.

Of course, everyone has their own needs, preferences, and priorities when it comes to choosing a pregnancy test—think: your budget and mental health—so the right test for you might not be the right test for everyone. Here are some things to consider when choosing an at-home pregnancy test:

• Ease of readability. One study found that for one particular brand, 87 percent of participants rated it "easy to read" but confused the meaning of the results based on the way “pregnant” vs “not pregnant” were displayed. If this is your primary concern, stick with a digital pregnancy test.

• Cost. Want to test often? Check out pregnancy strips (without the wand packaging), which can be found for less than 30 cents apiece.

• Sensitivity. There are a few at-home pregnancy tests that are sensitive to as little as 10mILhCG/mL urine. These are usually marketed as being able to test up to six days before a missed period, but if sensitivity is your priority, a blood test is going to be your best choice.

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Since the beginning of time, no matter who you are or where you’re from, if you think you’re pregnant, you really want to know. Right now.

Thankfully, we have at-home pregnancy tests. But while the boxes at the drugstore promise to tell you right now if you’re pregnant or not, remember: These things aren’t magic. They work by detecting the pregnancy hormone human chorionic gonadotropin (hCG), and—while these tests are quite sensitive—it takes time after conception for your body to produce a high enough level of hCG to get a positive result.

How does a pregnancy test work?

HCG is a hormone that your body begins to produce after an embryo implants in your uterine lining. Pregnancy tests can be performed either by urine testing at home, which is the most common, or blood tests that are done in a doctor’s office or lab.

In most at-home pregnancy tests, there is a wand that is either held under the urine stream or placed into a urine sample for a specified period of time. Then you wait for a result, which can take about three to five minutes, depending on the test.

Different tests have different ways of displaying results. Some have digital readouts that say “pregnant” or “not pregnant.” Others use lines or a plus or minus to show the result. With lines, you’ll always want to see the control line—this shows that the test worked. Then, if a second line appears, that indicates a positive result.

Over the years, tests have become increasingly sensitive. Today, some can detect 10 milli-international units (mIU) of hCG per milliliter (mL) of urine, although most pregnancy tests detect at 25mIU/ml. The more sensitive tests might catch a pregnancy a day or so before other tests, but after those first days, there is no advantage to the higher sensitivity, since levels of hCG double approximately every 48 hours in early pregnancy.

When should you take a pregnancy test?

You can take a pregnancy test whenever you want to, but it may be pointless if you take it too early. You’ll get the most accurate result if you wait until at least the first day of your missed period. By then, most at-home pregnancy tests give nearly 100 percent accurate results.

The earliest a test could pick up hCG would be eight days after ovulation, or five days before an expected period—although for many people, this is too early to detect hCG, and it is recommended to wait until the day of a missed period for more accurate results. The time between ovulation and the start of a period is called the luteal phase, and it lasts 14 days. It takes at least six days from ovulation to implantation (and can take up to 12), and it takes at least another two days for hCG levels to rise to detectable levels in the urine. However, even if you take an early pregnancy test five days before you are expecting to get your period, you could still get a false negative if you ovulated later than expected, implantation took longer than six days, or hCG levels were simply not detectable enough.