How We Calculate Your Pregnancy Due Date ?
Due date is the estimated date of delivery calculated by two methods, using last menstrual period and other one is using conception date.
LMP Method: Using LMP method, you can calculate the due date by adding 40 weeks i.e 280 days to first day of your last menstrual period (LMP). Pregnancy is considered from first day of your last menstrual period (if pregnant), menstrual period is the first week of the pregnancy and lasts for approximately 40 weeks, i.e. 9 months 7 days. So, adding this length from the first days of your LMP gives your estimated date of delivery (EDD). This method is known as Dr. Nagele's rule.
Conception Date Method: If you have kept track of your ovulation for that particular month and know on which day your egg must have been fertilized, you could calculate the date based on the conception date. Here the baby due date will be 38 weeks from the conception date.Only a few expectant mothers can accurately know when they have conceived. Your calculations might go wrong as you may not conceive on the day you had intercourse during your most fertile period. The sperm could remain in the fallopian tube for some days until it meets the egg, fertilization occurs, and then you will conceive.
This is why LMP method could be more suitable than the conception date method to calculate the estimated due date. The actual delivery date may be the same or different due to many other factors related to pregnancy.
Most Frequently Asked Questions around Due Date Calculators :
1. What is pregnancy due date or expected date of delivery(EDD)?
The expected date of delivery (EDD) is the date on which you are likely to give birth to your baby. It is calculated on certain assumptions and gives an approximate date, helping you to prepare for the ‘D’ day.
Around 280 days or 40 weeks is what is considered for calculation. To be exact, it is nine and one-third months or 10 lunar months.
2. Why is due date calculated from last period?
LMP is the first day of your bleeding during the last menstrual period. You bleed as the uterus sheds the lining formed during the previous cycle. Ovulation occurs around two weeks from LMP, and that is when you become fertile. If fertilization occurs during this cycle, the uterine lining (endometrium) grows to accommodate the baby, thus making you miss your next period.
LMP is also considered for calculation because the date is easier to remember!
3. How accurate are these due dates?
LMP may not be the best date for calculation as the actual ovulation and fertilization begin only after two weeks. However, it is a popular way to know your due date as most of the women cannot precisely identify when they have ovulated or conceived. There is no single method which can predict the exact date.
4. What are the other methods of calculating due dates?
Ultrasound scan, clinical examination of pelvic supported by exact menstrual records in the first trimester, Doppler ultrasonography after 10 to 12 weeks, and Human Chorionic Gonadotropin Pregnancy Test are some scientific methods to calculate the EDD.
5. Can my due date change?
EDD is often a tentative date, to make you prepare mentally, and also, take the necessary steps to welcome the baby home. The pregnancy period is usually 266 days or 38 weeks. A healthy delivery can happen anytime from 37 to 40 weeks.
What To Expect From Momjunction’s Pregnancy Calendar:
- Fetal age is calculated by taking the average length of the cycle as 28 days and average luteal phase length as 14 days.
- Our calendar tells you when the second and third trimesters begin.
- You can know the safe range to give birth. For example, if your LMP is 9 March 2016, your safe range will be between November 23 and December 28 of 2016.
- As you do not want to announce your pregnancy immediately after testing positive, we will tell you the right time to make the news public.
- The pregnancy calendar alerts you to the risks of miscarriage, and how far away you are from it.
Significant Milestones in Embryo / Fetal Development:
Use our calendar to know important milestones such as:
- The date when you have conceived.
- The day on which your pregnancy test proved positive.
- A time when your baby’s organs begin to develop and heart starts beating.
- The period when you can hear your baby’s heartbeat and other major organs form.
- The beginning of your second trimester when there is a lower risk of miscarriage.
- When your baby can see the light, hear sounds and develop nails.
- Know your baby's gender on ultrasound.
- When you can expect to feel your baby's movements.
- Weeks when premature babies have a chance to live.
- Third Trimester during which your baby will be able to breathe.
- During which week is your baby considered full term.
- Finally, when your baby is due.
Disclaimer: While our tool gives you a tentative due date and other details, it cannot replace a medical consultation. Visit a physician for confirming your EDD based on your complete medical history.
Our calculations are only an indication. MomJunction is not liable for any related issues, consequences or damages.
- 1. Baskett TF, et al. Naegele's rule: A reappraisal. BJOG: An International Journal of Obstetrics and Gynaecology. 2000;107:1433.
- 2. American College of Obstetricians and Gynecologists. Your Pregnancy and Childbirth Month to Month. 5th ed. Washington, D.C.: American College of Obstetricians and Gynecologists; 2010:13.
- 3. MacKenzie AP, et al. Prenatal assessment of gestational age. Accessed Apr. 15, 2016.
- 4. Cunningham FG, et al. Williams Obstetrics. 23rd ed. New York, N.Y.: The McGraw-Hill Companies; 2010. Accessed Apr. 15, 2016.
- 5. American College of Obstetricians and Gynecologists Committee on Obstetric Practice. Committee Opinion No. 579: Method for estimating due date. Obstetrics & Gynecology. 2014;124:863.
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