How to Determine Date of Conception by Calculation


How can I determine date of conception? This article will help you find date of conception, the estimated date of conception, due date, and how to tell date of conception using a pregnancy calculator and conception calendar.

For most women knowing the actual conception date is a nightmare. One cannot pinpoint the exact day. It gets worse when a woman has sex with different partners and conceives. She will be lost in finding the father of the baby because she cannot know when she actually conceived. This is because the sperm may live inside the vagina for 5-7 days.

How to Determine Date of Conception by Calculation
How to Determine Date of Conception by Calculation

However, a released egg from the fallopian tube waiting to be fertilized remains viable for 24 hours only. Healthcare providers on the other hand, cannot tell the due date once conception takes place. This makes pregnancy a game of estimation.

The conception date is estimated and so is the due date. Unless a couple chooses to use vitro fertilization to conceive, there is no pinpointing the exact day of conception or the date the baby is due.  Here is how to find date of conception as well as the due date.

Estimated Date of Conception

The estimated date is the expected date of conception based on may factors. The first factor has to do with the fact that you can conceive by having sex 5-7 days before ovulation.  This is because the sperm lives in the vagina for a maximum of seven days depending on its strength. A weak sperm would only survive for a maximum of three days.

Therefore, when you have sex 5 days before ovulation you are likely to conceive on the 5th day. This is when your basal temperature is higher than on the first day you had sex. Similarly, a strong sperm will have lived in your body for those five days to make a baby girl and if you conceive a boy, you will have to make love severally within the five days before ovulating so that the sperm responsible for a boy does not have to swim a long distance.

Secondly, healthcare providers assume that all women go through a 28-day menstrual cycle. When this is used as basis, most women are expected to conceive on the 14th day during ovulation. Women with longer menstrual cycles like 30 days, find date of conception later from 14th. They would probably ovulate on the 16th day of their menstrual cycle and hence be able to conceive.

Another assumption used to get the estimated date of conception is the date of the period. Some conception calculators will use the first day after the last period while others will use the first day of the period. These dates are based on the kind of ovulation calendar in use.

How to Determine Date of Conception

Conception dates as seen above are pure estimates.  Therefore, it is important to learn how to determine date of conception. You can do this easily by charting your ovulation. Invest in a fertility monitor and learn how many days your cycle lasts. If your menstrual cycle lasts for 24, 28, or 30 days, you can still be able to identify your luteal phase, which is the period after ovulation. Normally it is a half phase of two weeks or 14 days for all women regardless of the menstrual cycle. This is the prime period that one can probably conceive if they have sex.

The tip is to get the length of your cycle say 30 days and subtract 14 days. This therefore, means that if you have a menstrual cycle of 30 days your determined date of conception would be 16th. You can determine date of conception by having a clear chart of your cycle.

How to Calculate Date of Conception

Want to learn how to calculate due date of conception? You can calculate date of conception using the following methods.

First Day of Last Cycle + 14 days

If you have had your period, which ends today, then tomorrow would be your first day of last cycle. Using that date, you can find date of conception by adding the 14 days of ovulation. The result would give you either the exact day of conception or an estimate.

If you know your cycle length, the result would be clear-cut. However, if you were not sure about your menstrual cycle length you would have to add another five days to the outcome. The five days give allowance for the sperm that may have lived for longer. This means that if your first day of last cycle was on 9th +14 your conception date would be on 23rd for a regular cycle. For an irregular cycle, it would be 23rd-28th.

Reverse Due Date to Determine Conception Date

Another method of how to calculate date of conception is by reversing the due date. If your healthcare provider has already provided you with the date your baby is due, subtract the length of the pregnancy from that date. A pregnancy lasts 40 weeks or 280 days. The first two weeks of conception do not amount to something in this method of finding the date of conception. As a result, you will be expected to subtract 14 from 280 to get 266 days. From your due date, subtract 266 to get your actual conception date.

Date Of Conception Due Date

Date of conception due date comes from knowing when you conceived. If you are sure about when you ovulated and conceived, you can find the due date by adding 280 days. In this case, the 14 days of ovulation matter. The counting for due date begins even before you conceived. This will give you the 40 weeks or 10 instead of 9 months.

Date Of Conception Pregnancy Calculator

Finding the date of conception is easier with a pregnancy calculator. Conception pregnancy calculators can be found online and you just need to enter your first day of your last menses.  In addition, you will be required to give the length of your cycle. In instances where you have a due date, the conception pregnancy calculator can provide the date of conception as well.  With a push of a button, you get the date without manual complex calculations.  Some conception pregnancy calculators may also tell you:

  • The sex of the baby
  • The days you are most fertile in a certain period, for example in three months time
  • Due date
  • Conception dates dating back to 100 years.

Date of Conception Calendar

You can create date of conception using an ovulation calendar. Date conception calendar allows you to chart the days you are more fertile. This way, you will ensure to try to conceive on those days unlike other days of your menstrual cycle

More on Conception:

Read More on Pregnancy Signs and Ovulation.