Updated June 01, 2023

Pregnancy test calculator: Figure out when a pregnancy test is most accurate

If you think you might be pregnant, it can be tempting to reach for a test immediately. But how soon can you take a pregnancy test? Discover what early pregnancy tests are looking for and when you can take one using Flo’s pregnancy test calculator. 

Dr. Jennifer Boyle
Medically reviewed by Dr. Jennifer Boyle, Obstetrician and gynecologist, Massachusetts General Hospital, Massachusetts, US
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Whether you’re trying for a baby or not, the time between thinking you might be pregnant and knowing for sure (aka the two-week wait) can be stressful. No one likes living in uncertainty. You might not have even missed a period yet before thinking that you might be expecting. So, how soon can you take a pregnancy test? 

Understanding when to take a pregnancy test to get an accurate result can be a little bit of a waiting game. Guidelines suggest that you should wait until the first day that you’ve missed a period before you go out and buy a test. However, some early at-home pregnancy tests may be able to detect pregnancy earlier.

Here, Dr. Tiffanny Jones, reproductive endocrinologist and infertility specialist, explains the differences between early and normal pregnancy tests, what human chorionic gonadotropin (hCG) is (and why it’s so important), and when you can take a pregnancy test. 

Remember that pregnancy test calculators can help you learn more about what to look out for when taking a test and when you might want to take one. They are for informational purposes only. They cannot and should not be used to confirm a pregnancy. If you suspect that you might be pregnant, you should reach out to your health care provider who will be able to give you a more accurate result.

Is there a difference between pregnancy tests?

If you’ve ever looked at the pregnancy tests available at the store, you’ll likely have noticed that there are lots to choose from. It can be easy to feel overwhelmed. However, generally, pregnancy tests can be split into early pregnancy tests and standard pregnancy tests. 

Standard pregnancy tests are urine tests that can detect human chorionic gonadotropin (hCG — a hormone that your body releases in early pregnancy). This is the first indication that you might be pregnant. 

It’s recommended that you wait until the first day of your missed period or at least 21 days after you’ve had unprotected sex before you take one. Waiting might feel impossible, but this allows your body to produce high enough levels of hCG to be detected by the test so that your result is more likely to be accurate. 

Early pregnancy tests are more sensitive to hCG. They may be able to give you a positive result before you’ve missed your period. 

“Early pregnancy tests are urine tests that can detect very low levels of urinary pregnancy levels [more on this below], some as early as five days before a missed period,” says Dr. Jones. 

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When is a pregnancy test positive?

Let’s be real: Accuracy and reliability are probably the most important factors on your mind when it comes to a pregnancy test. Nobody wants to receive an inaccurate result.

When used correctly (if you follow the instructions on the box), standard pregnancy tests are advertised as being incredibly accurate, around 99%. However, the earlier you take a pregnancy test, the harder it is to detect hCG. While you can take a standard pregnancy test on the first day that you miss your period, it’s generally recommended that you wait at least a week for more accurate results and to prevent a false negative (where the test gives you a negative result when you are in fact pregnant).

Studies have reported that tests taken on the first day that you miss your period can be considered to have 90% sensitivity at detecting hCG. This rises to 97% if you wait one week after you’ve missed your period. 

When is an early pregnancy test positive?

While early pregnancy tests can be really useful if you’ve had an issue with your birth control, if you’ve been trying to conceive for a long time, or taking medication that may be damaging to a pregnancy, it’s important to note that they are considered to be less accurate. This is because your hCG levels are low at the very beginning of pregnancy, and the test may not be able to pick them up. This could lead to a false result. It’s rare for a test to give you a positive result when you’re not pregnant, but you may receive a negative result when you are pregnant if the test can’t detect the hCG in your pee. 

Your hCG levels rise throughout your first trimester. This is why the later you take a test, the more accurate it is.

Are there variations in hCG levels?

The key to knowing when to take a pregnancy test lies in when hCG might start showing up on tests. Your body starts to produce hCG in your blood and pee once the embryo (fertilized egg) attaches to your uterine wall. This can happen between six days and two weeks after the egg is fertilized (conception). HCG is considered to be one of the earliest indicators of pregnancy. 

Generally, your hCG levels will double every 48 hours in your first trimester, peaking at around 10 weeks. After that point, they’ll level off. However, hCG levels can differ from person to person, and Dr. Jones explains that detection of hCG levels can vary in very early pregnancy depending on when you take a test.  

“[The detection of] hCG levels can be negative in early pregnancy if they are tested too early,” she says. “This can be due to the level of detection of the test (if the test you take isn’t sensitive enough) or if [you take a test] too close to the time of ovulation.” This is because your body hasn’t produced enough hCG yet. 

If you do a pregnancy test that comes back positive, your health care provider may also give you a blood test to check your hCG levels.

When to take a pregnancy test

“The best time to check is after a missed period,” says Dr. Jones. As we now know, that’s due to the fact that your hCG levels will be high enough at that point for a standard test to pick up on them. But that two-week wait can be frustrating. Try to be kind to yourself during this waiting period. It can be difficult to ignore every twinge or flutter, but speak to loved ones if you’re worried and try to find things that relax and distract you until you can take a test. 

When to take a pregnancy test after a missed period

This is the golden time to take a pregnancy test. You can take a standard pregnancy test starting from the first day of your missed period. If it comes back positive, you can then reach out to your health care provider who will guide you on what to do next.

best time to take a pregnancy test

When to take a pregnancy test after ovulation

Ovulation describes the process in your cycle when your ovaries release an egg. There’s usually a 24-hour window when your egg may then be fertilized by sperm if you have unprotected sex. 

Knowing when you’re ovulating and when your fertile window is (the time in your cycle when you’re most likely to become pregnant) can help you understand any changes throughout your menstrual cycle. 

You should wait at least two weeks after you’ve ovulated before taking a pregnancy test. This is because it can take between 6 and 14 days for an embryo to implant in your uterine wall and for hCG to begin being produced.

When to take a pregnancy test after sex

If you’ve had sex without using birth control, then you may be curious to know when you can take a pregnancy test. The general guidelines apply here. If you track your period and have a regular cycle (you can track this using an app like Flo), then you can take a standard pregnancy test on the first day of your missed period. If you wait a week after your missed period, it’s worth knowing that you may get a more accurate result.  

If your cycle is irregular (this can be due to hormonal imbalances or stress, among other things), or you’re not sure when your period is due, then it’s recommended that you wait at least 14 days to take a pregnancy test after sex. 

If you don’t want to have a baby and have had unprotected sex, you can use emergency contraception within three to five days after having sex. 

When to take a pregnancy test while breastfeeding

While breastfeeding can impact your hormones, giving you a surge of the love hormone oxytocin, it doesn’t impact the outcome of pregnancy tests. Your body only produces hCG if you’re pregnant.

Missing a period is probably the clearest indicator in your mind that you may be expecting, but this can be a little bit tough to tell if you’ve recently had a baby, as your period may not have returned after you gave birth.

If you’re breastfeeding after giving birth, it can take between 9 and 18 months for your cycle to become regular again. This is totally normal, as your hormones change during breastfeeding, which can suppress ovulation. This means your chances of getting pregnant while you breastfeed are lower, but it’s not impossible. You may still ovulate within the first six months of giving birth, meaning you could get pregnant. And studies have highlighted that two-thirds of women ovulate before they have a vaginal bleed during the postpartum period. 

So, if you’re breastfeeding, having sex without using birth control, and think there’s a possibility you might be pregnant, you should take a standard pregnancy test on the first day of a missed period or two weeks after having unprotected sex. It’s important to note that your hCG levels will return to zero within 7 to 60 days after giving birth, so if you do a pregnancy test during this period of time, it may pick up on the hCG from your previous pregnancy. 

If you think you’re pregnant but don’t have the sign that your period is late to rely on, then you should reach out to your health care provider. Outline any symptoms you’ve had and explain when you last had unprotected sex. They should be able to help determine whether or not you’re expecting again.

When to take a pregnancy test after miscarriage

Miscarriage can be an intensely emotional and painful time. It’s also a time of immense physical change. It can take between four and six weeks for your hCG levels to drop following a miscarriage, and this can vary depending on how far along you were. 

Your health care provider may carry out a pregnancy test in the weeks following your miscarriage to confirm that all your hormones have returned to pre-pregnancy levels. If the test comes back positive, it could mean a number of things. Your health care provider will help you get it figured out.

Many health care providers recommend waiting until you have your next normal period before trying again for pregnancy. This will help make sure your body fully heals. Ask your provider what their recommendation is.

However, the American College of Obstetricians and Gynecologists explains that getting pregnant as soon as two weeks after having a miscarriage is possible if you’ve had unprotected sex. If this is the case, the hCG detected in the pregnancy test could indicate a new pregnancy. 

In this situation, rather than doing a pregnancy test at home, Dr. Jones suggests, “a blood test would be best.” Your health care provider will look at your hCG levels and may then repeat this test 48 hours later. 

“[Your hCG levels] rising by at least 35% can mean there is a new pregnancy. If they decrease, it can mean it is from the miscarriage,” Dr. Jones adds.

When to take an early pregnancy test

As we’ve seen, taking a standard pregnancy test can be a little bit of a waiting game. However, you’ll have the reassurance of knowing that they’re more accurate than early tests, so it could be worth the wait.  

If you think that you may be pregnant or you’re trying to conceive, you might decide the wait is too long and consider taking an early pregnancy test. The good news is that you can take a specially designed early pregnancy test five days before you expect your period. If you’re not exactly sure when that is, you can track your cycle using an app like Flo to work out when to take one. 

If the test comes back positive, reach out to your health care provider and follow it up with a standard pregnancy test either on the first day of your missed period or 21 days after you’ve had unprotected sex. 

How to take an at-home urine test

So, you think you might be pregnant and have gone out and bought a test. Now it’s time to actually do it. 

Both early and normal pregnancy urine tests can vary slightly depending on the brand you buy. However, they all detect hCG and, if you follow the instructions, can be really accurate. 

Once you’re ready to take a test: 

  • Read all the instructions included in the pack. Wash your hands and make sure you’re taking your test in a clean environment. 
  • Remove the pregnancy test from its wrapper. You will either need to pee directly onto the test or pee into a clean container or cup and then place the absorbent end of the test stick in the cup. Your test box will explain what you need to do. 
  • Once you’ve soaked the absorbent end of the stick in pee, place it on a flat surface, facing upward (make sure you can see the little results box).
  • You will then need to wait for your results to show. This can take between 1 and 10 minutes. Different brands of pregnancy tests have different reaction times. This is the amount of time it will take to see a result. Make sure you read the instructions carefully. 
  • Different brands present positive and negative tests differently, so it’s really important to read the box to understand your results. 

If your pregnancy test comes back positive, then you should reach out to your health care provider who will advise you on what to do next. 


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