Pregnancy Due Date Calculator

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No other excitement is the same as taking a pregnancy test and finding out a positive result! Once you’ve processed that news, the first question that comes to your mind will undoubtedly be: when is my due date? Even though it’s true that most pregnancies last 40 weeks, there are many other factors that have to be taken into consideration while determining your due date.

We’re here to put a lid on your worries and help you determine your estimated due date with the pregnancy due date calculator.

Due Date Calculation: How Many Weeks Pregnant Am I?

The estimated date of delivery (EDD), commonly known as the due date, is the estimated date when labor is expected to begin. This date which can be determined using a pregnancy due date calculator is just an estimate and only 1 in 20 people delivers on their estimated due date. You’ll probably start labor sometime in the two weeks before and after your due date.

Gestational Age Vs Fetal Age

There are two ways to measure the age of a baby during pregnancy, namely:

  1. Gestational Age
  2. Fetal Age


Gestational age is used to track pregnancy and calculate a due date. It measures how far along your pregnancy is in weeks. On the other hand, fetal age is the actual age of the growing baby.

Gestation is the time between the date of conception and birth. It is measured from your last menstrual period (LMP) — the first day of your last period — to the current date in weeks.

How To Calculate The Due Date?

A due date calculator uses four methods to determine your expected due date:

  1. Due date by the last menstrual period
  2. Due date by conception date or ovulation
  3. Due date by IVF transfer date
  4. Due date by ultrasound scan

Due Date Calculator: Last Menstrual Period

The common length of pregnancy is 280 days or 9 months. In this method, the due date is calculated by adding 280 days to the first day of your last period.

Note: This assumption is for a regular 28-day cycle (cycles can vary from 20 to 45 days), and the menstrual period and ovulation are considered to be the first two weeks of pregnancy. This method is not 100 percent accurate, as it is affected by the regularity of your menstrual cycle.

We’ve gathered all the information about these advanced formulas which are used by a due date calculator to determine the closest to accurate results.

Naegele's Rule

  • The standard method of calculating a due date for a pregnancy
  • Due date= LMP + 280 days
  • Considers a 28 days menstrual cycle to be 28 days with ovulation occurring around the 14th day of the cycle
  • For a longer cycle, the estimated due date will be later
  • For a shorter cycle, the estimated due date will be earlier

Mittendorf-Williams Rule

  • More advanced than Naegele’s rule
  • For first pregnancies, an average of 288 days from LMP
  • In subsequent pregnancies, an average of 283 days from LMP
    1. Determine the first day of your last menstrual period.
    2. Count back 3 calendar months from that date. 
    3. Add 15 days to that date if it’s your first pregnancy, or add 10 days for subsequent pregnancies
  • For first pregnancies, due date= LMP – 3 months + 15 days
  • For subsequent pregnancies, due date= LMP – 3 months + 10 days

Parikh's Rule

  • Used for irregular cycles
  • The expected date of delivery is calculated by adding 9 months to the last day of your menstrual cycle, subtracting 21 days, and then adding the duration of previous cycles.
  • Due date= LMP + 280 days – 21 days + the length of previous cycles (or, the average cycle length)
  • The risk of any potential errors related to calculating your expected due date is greatly reduced

Wood's Rule

  • Considers the individual length of the menstrual cycle as well as the number of pregnancies
  • Calculate your expected due date
    • For first pregnancies, the expected due date= LMP + 12 months – (2 months and 14 days)
    • For subsequent pregnancies, the expected due date= LMP + 12 months – (2 months and 18 days) = EDD
  • Use the expected due date in the equation according to your cycle length
    • For cycles longer than 28 days, due date= EDD + (actual length of cycle – 28 days)
    • For cycles shorter than 28 days, due date= EDD – (28 days – the actual length of your cycle)

Due Date Calculator: Conception Date

With this calculation, 266 days of pregnancy are added to the date you conceived. But there’s a little. You might know the exact date you had sex. But the exact conception date isn’t always known. This is because it can be challenging to determine the exact date of ovulation. Sperm can live in the female body for up to 5 days, and the egg can live for 24 hours after it’s released from the ovary.

Therefore, the conception date can be several days after you’ve had unprotected intercourse.

Due Date Calculator: IVF Transfer Date

According to the Centers for Disease Control and Prevention (CDC), more than 250,000 assisted reproductive technology cycles are performed in the United States each year. This results in about 77,000 or more babies born a year.

If you are part of the growing tribe of IVF moms, you can use the IVF due date calculator to determine your expected due date.

The IVF due date calculator can determine your baby’s due date in two ways:

  1. When you ovulate—meaning your egg retrieval or intrauterine insemination (IUI) day. In case you’re undergoing IUI, your due date is 266 days (or 38 weeks) later.
  2. Whether you’re having a three- or five-day embryo transfer. For a three-day embryo, count forward 263 days from the transfer for your due date. For a five-day embryo, add 261 days to the transfer for your due date.

Due Date Calculator: Ultrasound Scan

According to the American Academy of Obstetricians and Gynecologists (ACOG), the most accurate method to establish gestational age is a first-trimester ultrasound. So if you can’t pinpoint when you conceived, forgot the day of your last period, or aren’t sure when ovulation occurred, you can determine your due date at your first prenatal appointment.

Your OB or midwife is most likely to schedule you for an ultrasound to confirm the pregnancy, during which, the technician or physician will measure the baby’s length, from crown to rump, to gauge how far along you are and calculate your due date. If the baby is much bigger or smaller than expected for the gestational age based on your LMP, your doctor will likely change your due date based on what they see on the first-trimester ultrasound.

Final Word On Due Date Calculator

The average pregnancy is calculated at 282 days (40 weeks) from the first day of your last period. But babies rarely keep to an exact timetable. So, a full-term pregnancy can be anywhere between 37 and 42 weeks. Our due date calculator will help you determine the closest to the accurate due date. So sit back and enjoy the pregnancy because you’re soon going to experience parenthood bliss!

FAQs

1. Can I plan my due date?

It is possible to get pregnant when you really want to. But you probably won't be able to map out exactly when you'll give birth to the day (or even the week or month!).

2. Can my due date change?

Yes, your due date can change. There's no reason to worry, but your doctor may change your due date for a number of reasons as your pregnancy progresses.

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

The estimated date of delivery (EDD), commonly known as the due date, is the estimated date when labor is expected to begin. This date is just an estimate and only 1 in 20 people delivers on their estimated due date. You’ll probably start labor sometime in the two weeks before and after your due date.

4. How to calculate the due date?

A due date calculator uses four methods to determine your expected due date:
  • Due date by the last menstrual period
  • Due date by conception date or ovulation
  • Due date by IVF transfer date
  • Due date by ultrasound scan
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