Our easy-to-use pregnancy calculator is the most popular way to calculate your due date based on the date of your last menstrual period, conception date, IVF transfer date, or the date of your last ultrasound. By entering either of these dates, the calculator provides a reliable estimate of your due date, helping you track your pregnancy with ease.
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. Meaning 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) (or choosing that option from our tool’s menu above). And that’s how most healthcare providers do it.
If your menstrual cycle length is the average length (28-day cycle), your period 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 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.
If you know the first day of your last menstrual period, you can use our Due Date Calculator to predict your estimated due date.
Formula: Due Date = LMP + 280 days
You can also subtract three months from the first day of your last period and add seven days.
Formula: Due Date = LMP − 3 months + 7 days
Or choose “last period” from the choices in our Due Date Calculator menu, above.
The first day of your LMP is how most health care providers estimate a baby’s due date.
Conception date
If you’ve been tracking ovulation symptoms or have been using ovulation test strips, you may be able to use your conception date to see how far along you are and when the baby is likely to arrive.
Just add 266 days to get your estimated due date. Or select “conception date” and let our pregnancy Due Date Calculator do the math for you.
IVF transfer date
If you conceived through in vitro fertilization (IVF), you can calculate your due date using your IVF transfer date. Most embryo transfers occur either three days or five days after egg retrieval and fertilization.
If you had a day-three transfer, count 263 days from the transfer date to calculate your due date, and if you had a day-five transfer, count 261 days. Or use our IVF Due Date Calculator to find out the big day!
Ultrasound scan
Even if you can’t pinpoint when you conceived, forget the day of your last menstrual period, or aren’t sure when ovulation occurred, the date of an early ultrasound, if you have one, can help your practitioner determine your due date at your first prenatal appointment or another prenatal visit in your first trimester.
The timing of an early ultrasound can sometimes more accurately date the pregnancy than your LMP and other methods. Just choose “ultrasound” from our Due Date Calculator choices.
Just be aware, however, that not all women get an early ultrasound. Some practitioners perform them routinely, but others only recommend one if your periods are irregular, you’re 35 or older, you have a history of miscarriages or pregnancy complications, or the due date can’t be determined based on your physical exam and LMP.
Other clues can help your health care provider figure out how far along you are and better pinpoint your due date at your prenatal check-ups.
- Pregnancy milestones such as the first time the baby’s heartbeat is detected (around week 9 or 10, though it can vary) and when you first feel fetal movement (on average between 18 and 22 weeks, but it can be earlier or later), can give clues as to whether your due date is accurate.
- Your fundal height, which is the measurement from your pubic bone to the top of your uterus, is checked by your practitioner at each prenatal visit and helps confirm your due date.
- The size of your uterus, which will be noted when your initial internal pregnancy exam is performed, can also be a factor in pinpointing the EDD.
Due date as a reference point
Generally, the point within the 37 to 42-week window at which the baby is born is not a cause for concern. Babies born between 37-39 weeks, 39-41 weeks, and 41-42 weeks are considered early term, full-term, and late-term, respectively.
Under normal circumstances, babies born within any of these ranges can be healthy, though full-term babies generally have better outcomes. Babies born before 37 weeks are considered preterm, or premature, while those born after 42 weeks are postterm.
These ranges are important as a reference for doctors to determine whether or not any action is necessary. For example, if a woman goes into labor too early at 33 weeks, doctors may stop labor to avoid a preterm baby that can have a host of health issues due to underdevelopment.
Conversely, if a woman has not gone into labor after 42 weeks, doctors may induce labor.
One possible complication of allowing the pregnancy to proceed beyond 42 weeks is that the placenta, which is responsible for providing nutrition and oxygen to the baby, can stop functioning properly, while the baby continues growing (requiring more nutrients and oxygen), which would eventually lead to a point in the pregnancy where the baby can no longer be adequately supported.
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 pregnancy 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 out what your baby’s sign and birthstone will probably be and a few famous people who 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 pregnancy calculator or from your doctor or midwife. Only 1 in 20 women delivers on her 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.
Frequently Asked Questions
How is my estimated due date calculated?
Calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP), this standard clinical method provides a helpful baseline for your journey. This approach assumes a 28-day cycle with ovulation at the midpoint. While this is the most common starting point, your healthcare provider may refine this date based on early ultrasound measurements.
What if I don’t know the date of my last period?
“When menstrual cycles are irregular or the last period date is unknown, a dating ultrasound is used to determine an accurate due date.” This clinical scan measures the baby’s length to establish a precise pregnancy timeline. Understanding your timeline early can provide significant peace of mind as you begin planning your prenatal care.
How accurate is an estimated due date?
“An estimated due date is a helpful target, but only about 5% of babies are born on their exact date.” It is natural to feel eager for your baby’s arrival, so it helps to view this date as a window rather than a fixed deadline. Most healthy pregnancies delivered between 37 and 42 weeks are considered full-term.
Can my due date change during pregnancy?
“Yes, a due date may be adjusted during the first trimester as more clinical data becomes available.” As your baby grows, ultrasound measurements provide a more precise view of development than a calendar alone. Your provider will update your roadmap to ensure you receive the most accurate and compassionate care at every stage.
How many weeks pregnant am I today?
“Pregnancy is measured in gestational weeks starting from the first day of your last period, rather than the day of conception.” This clinical standard means you are technically considered “two weeks pregnant” before conception occurs. Understanding this helps you align your personal timeline with your doctor’s prenatal appointment schedule.