Finding out conception date

Conception Date Calculator | When Did I Conceive?

Created by Dominika Śmiałek, MD, PhD candidate

Reviewed by Dominik Czernia, PhD and Jack Bowater

Based on research by

“Committee Opinion No 700: Methods for Estimating the Due Date.“ Obstetrics & Gynecology (May 2017)See 1 more source

Kessler J, Johnsen SL, Ebbing C, Karlsen HO, Rasmussen S, Kiserud T. “Estimated date of delivery based on second trimester fetal head circumference: A population-based validation of 21 451 deliveries.“ Acta Obstetricia et Gynecologica Scandinavica (October 2018)

Last updated: Dec 22, 2022

Table of contents:

Conception date - when did I conceive and how many weeks am I?
Conception calculator based on due date
Conception calculator based on LMP
Practical example of the use of conception date calculator
Can the pregnancy conception calculator be wrong?
First signs of pregnancy
FAQ

This conception calculator helps you to estimate the conception date of your child. Is your period late? Are pregnancy tests show clear results? Congratulations! Or perhaps you're not pregnant yet, but want to have a kid on an exact date? Don't hesitate - the pregnancy conception date calculator also works in reverse - it tells you when to conceive if you want a child born on a day of your choosing.

With our conception calendar calculator, not only do you get an answer to the question when did I conceive and how many weeks am I pregnant?, but you can also learn a bit about when does conception happen, and how long does conception take.

Conception date - when did I conceive and how many weeks am I?

Do you remember the moment you realized you were pregnant? After the initial excitement, you probably estimated your due date with a due date calculator. And after that, you might have gotten curious about the day you conceived. This conception calendar calculator will help you put all your doubts aside.

We know that having children changes your life completely. It affects your daily plans, holidays, and overall free time. Some say that it's easier for a kid to be the oldest in their class - they tend to be more mature and gain new knowledge easier. That's only one of the reasons you might want to have your child's birthday thought out well ahead. Although whether mother nature will allow you to keep such plans is another story, you can still use this pregnancy conception calculator to estimate when you should conceive to have a kid on a certain date.

Conception calculator based on due date

So, what day did I conceive? There are two ways to use our conception calendar calculator.

The first way is to provide the birth due date. When you visit the doctor, they will most likely perform an ultrasound. Although the doctor can see the baby from the 5-6th week of pregnancy, the best time to go for the first sonography is between weeks 8 and 12.

Based on the characteristics of the image and the results of your [blood test, compared with hCG levels calculator, the due date and week of pregnancy can be determined. Remember that those dates, as well as the conception calendar, are only an estimation and may change during the next visit.

Pregnancy typically lasts around 40 weeks (counted from the first day of your last period). That is 266 days from the conception date. If a baby is born before week 37, it's called premature birth. But don't worry if the due date changes or you go into labor on a different date - only 4% of babies are born on their due date, and 80% are born either two weeks before or after the date.

Let's go back to the question: what day did I conceive? In our conception calculator, we subtract 266 days from the estimated due date and get the most probable day of conception:

due date - 266 = conception date

Conception calculator based on LMP

The other method of using the pregnancy conception calculator is to provide the first day of your last menstruation (LMP) and the average length of your menstrual cycle. The majority of cycles last around 28 days. However, typical values range between 21 and 35 days.

In cycles of 28 days, ovulation happens around 14 days before the beginning of the next cycle. So, if a cycle lasts 28 days, ovulation occurs the 14th day after the first day of the cycle (the first day of bleeding). If it's shorter, you subtract the corresponding number, e.g., for a 22 days cycle - ovulation occurs on the 8th day. If it's longer, you add some days, e.g., for a 34-day cycle - ovulation is on the 20th day. For cycles longer than 35 days or shorter than 21 days, these calculations are not applicable, and you should consult by a doctor. If you're not sure how long your cycles are, leave the default number of 28 days.

When does conception happen? How long does conception take? The fertile window begins 3-5 days before the ovulation date and ends one day after it. It means to get pregnant, you should have intercourse within this time. Although sperm can survive up to 7 days inside a woman's body, conception does not happen until ovulation. Therefore, conception day is the day of ovulation (use our ovulation calculator to quickly check it) and might last for 24 hours after the egg is released. Therefore, the formula to estimate the conception date based on the LMP:

LMP + cycle length - 14 = conception date

Practical example of the use of conception date calculator

Let's take Anne. She is 11 weeks pregnant and still doesn't know her conception day. The first day of her last period (LMP) was 11 June 2018, and typically, her cycle lasts for 31 days (still in the range between 21-35). As mentioned before, we can assume that her ovulation began around 17 days after her LMP, on 28 June 2018.

11th June 2018 + 17 days = 28th June 2018

She conceived around her ovulation date (as a woman's egg can last up to 24 hours), on 28 June 2018. However, instead of all this counting, she used our pregnancy conception calculator.

Next up is Maggie. She just came back from the doctor, who told her that the due date is on 19 September 2019. Now, she has one question: 'what day did I conceive?'.

19th September 2019 - 266 days = 26th January 2019

You don't have to do the calculations by hand! Just put the numbers into our conception date calculator based on the due date. It can also work as a pregnancy week calculator, giving you an estimated week of pregnancy and the first day of your last period.

Can the pregnancy conception calculator be wrong?

Yes, of course. So, when does conception happen? There is no possibility being 100 % sure about it. You may be a little bit more certain if you track your cycle and have it perfectly regular. But even ultrasounds and blood tests aren't faultless. Remember, that your fertile window begins up to 5 days before ovulation and ends one day after it. So, although your conception date is, e.g., 11 July 2019, the intercourse that caused the pregnancy may have occurred as early as 6 July. However, with our conception calendar calculator, you can make an estimated guess!

Is your period late? Do you have some of the symptoms listed below?

Tender, swollen breasts
Morning nausea
Food aversions or cravings
Constipation
Mood swings

You might be pregnant! Congratulations. Now it's time to take a pregnancy test and make an appointment with a doctor.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

FAQ

How accurate are conception dates?

No conception date calculator is completely accurate, as they are estimating the date it occurred. The most accurate measure is to take an ultrasound and have a professional estimate the age of your baby for you. This service, however, will likely cost you though, so use best use an online calculator.

Does alcohol affect conception and implantation?

Moderate drinking does not impact fertility or the risk of miscarriage in regular pregnancy, a number of studies have found. However, if you are trying for a baby using IVF, both partners should not consume any alcohol. The woman should always stop drinking as soon as she finds out she is pregnant.

Where does conception occur?

Conception occurs in the fallopian tubes, more specifically the ampulla, where the oviduct curves around the ovary. The egg releases large amounts of progesterone here, which the sperm are attracted to. This is how the sperm know how to reach the egg.

When should I take a pregnancy test calculator based on conception?

You can estimate the day you conceived on as soon as you know you have missed your period. This is also the best day to take a pregnancy test. Use Omni Calculator to work out your conception date quickly and easily.

What is conception date?

Conception date is the day on which a baby was conceived, that is, the day on which the father’s sperm fertilised the mother’s egg.

How far along am I based on conception?

Calculate the number of full month differences between today’s date and your conception date.
Calculate the number of days in each of the months in step 1.
Work out the number of days from the conception date until the end of that month.
Find the number of days from the beginning of this month until today.
Add together the result of step 2, 3 and 4. This is how far along you are.

When is my conception date?

To find your conception date, you will have to perform some calculations to estimate it. Find out on what day your last period began, and add your average cycle length in days to that date. Finally, subtract 14 days and you will have an estimate of conception date.

Dominika Śmiałek, MD, PhD candidate

To calculate the conception date, please enter the due date or the first day of your last period (LMP).

Due date

First day of your last period (LMP)

My average cycle duration

I am in week

of my pregnancy

I conceived on

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Calculate your due date: How to find your baby's due date

Choose a calculation method Last periodConception dateI know my due date

First day of my last period

BabyCenter's Due Date Calculator

Use our pregnancy due date calculator by plugging in either the date of your last menstrual cycle or the date you know you conceived. The calculator will do the rest.

How is my due date calculated?

There are several ways your due date is determined. If you happen to know the day you conceived, you can count 38 weeks from that day to find your due date. (Human gestation takes about 38 weeks.)

But very few expectant moms know exactly when they conceived. Even if you only had sex once during your fertile period, you wouldn't conceive on that day unless you happen to be ovulating. Sperm can live for up to five days inside your fallopian tubes. So, it could be up to five days after you have sex that you release an egg (ovulate) and it gets fertilized by a waiting sperm. That's the day you conceive.

So, without knowing the day of conception, how does anyone determine a due date?

First day of your last period

The most common way to calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period (LMP). And that's how most healthcare providers do it.

If your menstrual cycle length is the average length (28-day cycle), your menstrual cycle probably started about two weeks before you conceived. This explains why pregnancies are said to last 40 weeks instead of 38 weeks.

This method doesn't take into account how long your menstrual cycle actually is or when you think you might have conceived. But generally speaking, women typically ovulate about two weeks after their menstrual cycle starts. And women are more likely to know when their last period started than the day they ovulated.

Conception date

If you do happen to know precisely when you conceived – say, if you were using an ovulation predictor kit or tracking your ovulation symptoms – you can calculate your pregnancy due date based on your conception date. Just choose that calculation method from the pulldown above and put in your date.

Note: Again, you don't necessarily conceive on the day you have sex.

IVF transfer date

If you conceived through IVF, you can calculate your due date using your IVF transfer date. If you had a Day 5 embryo transfer, count 261 days from your transfer date. If you had a Day 3 embryo transfer, count 263 days.

Can my due date change?

Your healthcare provider might revise your due date if your baby is measured during a first trimester ultrasound scan and found to be much bigger or smaller than expected for gestational age. This is more likely to happen if you have an irregular menstrual cycle length that makes it hard to pinpoint the date of conception.

Your healthcare provider will measure your baby during that ultrasound exam to figure out how far along your baby is and then provide you with a new due date.

What if I already know my due date?

If you already know your due date, you can use this calculator to see your pregnancy timeline. It will tell you when you'll hit various milestones, and when you may be due for prenatal tests and prenatal visits. You'll also find what your baby's sign and birthstone will probably be and which famous people were born on your due date.

How likely am I to give birth on my due date?

Of course, a due date calculation is always approximate, whether it's from our tool or from your doctor or midwife. Only 1 in 20 women delivers on their due date. You're just as likely to go into labor any day during the two weeks before or after.

Want more information about how the weeks, months, and trimesters of pregnancy are counted? See our pregnancy timing chart.

How soon can I take a pregnancy test?

With all this talk about pregnancy due dates, you may be wondering when you can take a pregnancy test. To ensure you get the most accurate reading, it's best to wait a few days after your missed period to take a pregnancy test.

At-home urine tests measure the amount of hCG (human Chorionic Gonadotropin) present in your body. If you take a pregnancy test before you miss your period, you may not get an accurate result, despite what some tests advertise.

If you're getting a blood test in your provider's office, you may get results sooner. These tests also measure the amount of hCG in your bloodstream, but they're more sensitive than at-home urine tests. Blood tests may be able to detect pregnancy six to eight days after ovulation.

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How do I know exactly what day I got pregnant?

August 21, 2020

Many women are very concerned about this issue, because the more accurately you can determine the date of conception, the easier it will be to predict the date of birth of the baby. But is it realistic to determine the exact date of conception and how to do it? Let's find out.

First of all, you should know that the date of conception always coincides with the date of ovulation, since the egg remains viable only for the first day after leaving the follicle. Another issue is that few women can accurately determine the day of ovulation - only ultrasound control will show this with absolute accuracy. nine0005

The second point worth knowing is that the date of sexual intercourse will not always be the date of conception. Why? Because spermatozoa remain viable in the uterus for 4-7 days, which means that pregnancy can occur even a week after sexual contact.

How then to determine the day of pregnancy? Here are some methods.

Early ultrasound.

If ultrasound is done for up to 7 weeks, then the date of conception can be determined most accurately, with an error of 2-3 days. During this period, the embryo develops proportionally and its size is approximately the same in all women. At later dates, the size of the fetus can vary greatly, so it will be almost impossible to calculate the exact day of conception. nine0005
Last period.

This method is quite accurate, but only if you have a stable, regular cycle. To determine the date of birth, you need to add 280 days to the day of the last menstruation. To simplify the calculation, you can use the following formula: subtract three months from the month of the last menstruation, and add 7 days to the day of the last menstruation.
First fetal movement.

Not the most accurate method, but still helps to determine the approximate gestational age. Usually, women begin to feel the movement of the baby at 18-20 weeks. Thin and multiparous women can feel the movement of the fetus as early as 16 weeks. nine0005

So, as you can see, the most reliable ways to determine the exact date of pregnancy is the day of ovulation and ultrasound in the early stages. That is why it is important not to delay with an ultrasound and visit a doctor as soon as possible after a positive result of a rapid pregnancy test. The best way to do this in a comfortable atmosphere is to choose our medical center. Here are friendly and highly qualified specialists who will answer all your questions.

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How to find out the date of conception of a child, find out the date of birth by the date of conception

The most important period in the life of any woman is pregnancy. The development of the child and his health will depend on how it goes. For some romantic natures, the day of conception of a child can be a significant date. They will celebrate this day as a significant event in their lives. The fact that many young women attach importance to this day may seem ridiculous. However, not only mothers, but also their doctors strive to find out the date of conception. Because it's really important information. nine0005

Why do you need to know the day of conception?

The fact is that it is necessary to determine the date of conception of a child in order to be able to follow the course of the development of the fetus, as well as to know the exact timing of pregnancy. After all, every week the fetus reaches a certain level of development. To control how favorable the pregnancy is, whether the fetus is lagging behind in its development, the doctor must clearly know the exact date of conception.

The exact gestational age will also allow you to calculate the expected date of birth, as well as the date the woman goes on maternity leave. nine0005

Determining the timing of pregnancy

Doctors distinguish between two types of terms - obstetric and true terms of pregnancy. The first is calculated based on the following factors:

the beginning of the maturation of the egg, which should be fertilized by the sperm;
when the zygote descends into the uterus;
when a fertilized egg with an embryo is formed;
when the fetus is formed.

This calculation is carried out starting from the first day of the last menstruation. nine0005

The actual gestational age starts from the day of ovulation and the day of conception. Usually the true term is 2 weeks behind the obstetric one.

Determining the day of ovulation

The day of ovulation occurs in the middle of the menstrual cycle. Depending on the length of the menstrual cycle, the day of ovulation is also calculated. It is on this day that unprotected sexual contact will lead to the fertilization of the egg.

You can determine the date of ovulation by measuring your basal body temperature. However, this is not the only way to determine the day of conception of a child. The day of ovulation can be determined by ultrasound. You can also use the program to calculate ovulation. nine0005

Knowing the timing of ovulation helps determine a favorable day for conception. This is important for those who plan to have children at a certain time.

Determination of the day of conception

The exact date of the conception of the child will determine the exact gestational age, and, therefore, will make it possible to follow the course of its development. In addition, you can find out the date of birth of a child by the date of conception.

To find out the date of conception of a child, you need to remember two dates:

the date of the first day of the last menstruation; nine0020
day when there was sexual contact.

Women do not always remember these dates. Therefore, when planning conception, it is worth keeping a calendar and marking the number and duration of menstruation.

And here it would be appropriate to give one more piece of advice - along with keeping the calendar, you should start taking vitamins for expectant mothers, which contain enough folic acid, preferably in the form of extrafolate, which is easily absorbed (for example, Pregnoton Mama). The fact is that the need for folic acid increases dramatically immediately after conception, and its deficiency in the first weeks after conception can lead to congenital malformations of the child. Since the exact date of conception can be determined after conception, it is better to provide the body and the unborn child with all the necessary micronutrients in advance.