Ways & How

How to Calculate Pregnancy Due Date

How to Calculate Pregnancy Due Date

After the nail-biting suspense of waiting for the pregnancy kit results comes the expectation of the baby’s birth. The expectant mother looks forward to the future, and needs a timeframe to plan and do many other things, including decorating the nursery, stocking up on supplies, saving up for anticipated expenses, booking the hospital and doctor visits, and preparing mentally by reading guides, consulting experienced mothers, and attending classes. There are many online calculators and apps to help women who don’t know how to calculate pregnancy due date. But it helps to understand how these calculators determine the approximate date.

  1. Follow Naegele's Rule

    Naegele's Rule is a simple method for determining the baby’s due date, and is easy for those with regular menstrual cycles. Naegele was a German obstetrician who came up with this formula a century and a half ago: Identify the first day of your last period, subtract three months, and then add seven days. The end date is the baby’s due date.

    illustrate, if the first day of your last period was June 23, minus three months is March 23, plus seven days is March 30, the estimated due date. This rule assumes a 28-day menstrual cycle. Those who have different menstrual cycles should adjust the date accordingly. If you have a 24-day cycle, subtract four more days. So based on the dates given in the above example, the final estimated due date should be March 26.

  2. Base it on the basal body temperature (BBT) and luteinizing hormone (LH)

    Those whose menstrual cycles are too irregular to follow, and who have intently tracked their ovulation dates by measuring their basal body temperature and luteinizing hormone levels can put those figures to another use. Since an increase in BTT and the LH level pinpoints the exact date of ovulation, adding 266 days to that date will give you the probable due date.

  3. Count to nine

    Since it’s common knowledge that pregnancies last nine months, you can simply identify the first day of your last period, then add nine months and seven days to that date. Doctors usually hesitate to count in months, preferring to count in weeks instead. This is because not all months have the same number of days. Weeks are relatively more precise. A full-term pregnancy lasts anywhere between 38 weeks and 42 weeks.

  4. Add to the conception date

    Pregnant women with a good memory of the date when the baby was conceived only have to count 266 days from the conception date to get the pregnancy due date.

    You will also learn your due date when you have your first pre-natal visit to your doctor while you are around two weeks pregnant. Your doctor knows how to calculate pregnancy due date using a number of methods. But if you follow the steps above, you will feel more involved and knowledgeable about your pregnancy. Do not be alarmed if your calculation is different from that of your doctor’s. The doctor’s calculation may be more accurate because of more high-tech methods. However, the reality is that the baby will come out when he or she is ready.

Only 5% of babies are born on the estimated due date; 80% are born within a ten-day range of the estimated due date. That’s a twenty-day window, which may be too long for some expectant mothers. The remaining twenty percent either give birth prematurely or a bit later. The doctor won’t allow the baby to stay too long in the womb, so a caesarean section, which can be scheduled, is a possibility for post-term pregnancies.


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