Due Date Calculator: How to Calculate Your Due Date

Pregnancy takes an average of 9 months (280 days) from day one of your last menstrual period (LMP). The first day of your LMP is also regarded as the first day of pregnancy. But, you may not conceive on this first date. Conception probably occurs about two weeks after the first day of LMP.  Have you ever wondered how they mathematically calculate your due date? Or you're baby feels really big and you want to check if what the doctor says is really true? If you have this blog and Pregnancy Pukeology Podcast is perfect for you, and if you don't have time to read just listen.

How to Determine Due Date

Determining the due date is not certain. Still, most women don’t give birth on their exact due dates. Having an idea of when you are likely to deliver is important. But still, it is only an estimation, don’t be so sure about it.

You will only give birth when your baby is ready which can occur anytime between 38 and 42 weeks. If you are not certain about your due date, seek the help of your health care provider.  Your OBGYN can do an ultrasound measure the baby and all the vital organs and guestimate your due date.  They consider the first ultrasound the gold standard for a reliable due date and you can back track just in case problems arise during the pregnancy to make sure your baby is growing appropriately. If you’re interested in how does an ultrasound work, listen to Episode 25 what is a sonogram?

Due Date Calculator/Birth Calculator

The estimated due date (EDD) is the date that the beginning of labor is likely to occur. It may be approximated by adding 280 days (9 months and 7 days) to the first day of the last menstrual period (LMP).  

Still, the accuracy of the estimated due date will rely on the memory of the mother. If you have a regular 28-day cycle, assuming that ovulation and conception happened on day 14 of your cycle, you can use the LMP to determine your due date.

Ways to calculate your due date if your menstrual cycles are regular (after every 28 days)

 

Naegele's rule

This rule involves a basic calculation where you add seven days to the first day of your LMP and then subtract three months. Here is an example:

If your LMP was January 2, 2020:

• Add seven days (January 9, 2020)
• Subtract three months (October 9, 2020)

Therefore, your due date will be October 9, 2020

What if your LMP was 29, December 2019? When is your EDD? Use the Naegele’s rule to determine the EDD.

Pregnancy wheel

The pregnancy wheel is a common method used by doctors to calculate due dates. The pregnancy wheel makes it easier to estimate your due date. It works by first locating the date of your last menstrual period on the wheel. Lining up the date of LMP with the indicator displays your due date.

How to Calculate Conception Date

If you have a regular period, you are likely to conceive in about 2 to 3 weeks (11-21 days) after the first day of your last period. Knowing when you ovulated (released the egg) is very challenging and that is why, just like most women, fail to know the exact date of conception. Thus, your conception date is an estimate based on day one of your last period.

IVF Due Date Calculator

In vitro fertilization (IVF) a special case in which your healthcare provider will know the exact date you conceived. Although no due date is guaranteed, IVF due dates tend to be more accurate than those in natural pregnancies.

There are various ways of calculating your due date based on the type of IVF you had. These include:

Egg Retrieval Date

Add 266 days (38weeks) to egg retrieval date if you IVF with your own eggs, with fresh donor eggs cycle or fresh donor embryos.

Transfer Date

Add 266 days (or 38 weeks) if you had IVF with 3 Day frozen embryo transfer FET then subtract 3 days (for the embryo). Subtract the exact age of the embryos in cases where your embryos’ age is more than 3 days.

Add 266 days (or 38 weeks) if you had IVF with 5 Day FET then subtract 5 days (for blastocysts). If the blastocysts’ age is more than 5 days, subtract their exact age.

How can you tell if your ovulating?

Most of you lovely ladies are past this point, because you were ovulating, had sex, got pregnant, and now that’s history, but some of my listeners are women who want to conceive (this one’s for you)! Research shows that when a women’s ovulating her behavior changes.  From the way she dresses to the way she flirts. Studying a women’s ovulation behavior can help companies sell ovulation detection kits, marketers targeting clothes or jewelry, and even boosting their online dating prospects (lots of swiping). The work also suggest that the type of birth control pill a woman is on or off could influence a woman’s choice in men.  I find this all so fascinating, but the physician in me wants to see the data. 

A women when ovulating supercharges their “femininity” as an innate subtle strategy to both attract the most desirable guys and convince them to stick around as shown by the evolutionary psychologist Greg Bryant from the University of California. Studies in the 1990’s showed a female spiked interest for muscular masculine men with deeper voices and symmetrical faces because men like George Clooney have dominant social roles meaning better genes and stronger immune systems.  Social psychologists found that women are most likely to cheat on their partners while ovulating for the same drive for hyper-masculine men, when they were unhappy with their current partners.

Men can actually smell a fertile woman?!?! The journal of Psychological Science found that men prefer the smell of a women who is more fertile in a blind smell test of t-shirts when they were ovulating verses the smell of women when they weren’t. The journal of Evolution and Human Behavior found that lap dancers got higher tips when they were most fertile. And the reasons why will astound you.

A woman’s body goes thru lots of changes while ovulating.  Subtle but detectable upward shifts in voice pitch happen, and her voice is highest the day she releases an egg. Bryant found that ovulating women sway their hips more when they walk and stand more defensive in their upper body.  Think the Kim Kardashian stance and walk. Fertile women also want to be in social settings and tend to show more skin when they go out. The journal of Consumer Research showed that women are drawn to sexier outfits, shoes, and accessories and they want to dress that way not to attract men but to out-beat other women, cat fight! The pupils of a woman’s eyes become larger in diameter with anything causing sexual stimulation during ovulation, and get the widest when a picture of their mate is shown to them.

Family Planning Method

A women’s body temperature slightly increases by 0.5-1 degree Fahrenheit because of the hormone progesterone during ovulation, and is used in some religious entities that do not believe in birth control as family planning. Family planning method must be taken from your basal body temperature (BBT).

Measuring BBT

• Take vaginal temperature after waking up while still lying in bed before you sit up
• Take your temperature every day at the same time
• Use a special thermometer for precise rounding with accuracy of 0.10 degree Fahrenheit
• Make notes of days that are unreliable. For example: changes in sleep patters, disturbed or interrupted sleep, jet lag, heavy drinking the night before, illness, medications, because these can cause your menstrual cycle to change.

Breastfeeding moms who want to have another baby soon, not immediately after, may want to consider the family planning method of temperature so they don’t have to go on hormonal birth control supplements. Remember that the typical body temperature ranges from 97 to 99 degrees Fahrenheit but vary between women.  Any rise in your basal temperature of 0.5 to 1.0F means your ovulating!