Reverse Due Date Calculator – How Does It Work?

Reverse Due Date Calculator - How Does It Work?

A reverse due date calculator works just the opposite of how a due date calculator works. Unlike the regular due date calculator, which considers the date of last menstrual period (LMP) to figure out the due date of delivery, the reverse calculator uses the due date of the delivery to ascertain the window frame when the woman might have conceived. Also known as the backward pregnancy calculator, the tool is said to be quite accurate in narrowing down the time frame when one may have conceived.

What Is a Reverse Due Date Calculator?

A reverse due date calculator or a reverse conception date calculator is a tool by which a pregnant woman can calculate the approximate period of conception if she knows the due date of delivery. With this method, the pregnancy is counted backwards, starting from the expected due date to a time frame when a pregnant woman may have conceived.

What Is the Need and Importance of a Reverse Conception Calculator?

When a pregnant woman goes for her first ultrasound, the gynaecologist usually gives a due date of delivery. While some women are convinced with this information, there are others who wish to find out when they might have actually conceived. This is when the reverse birth calculator comes into the picture. But this is not the only reason why a reverse conception calculator is needed; there are various reasons why we need them today. Let’s find out what they are:

  • A woman who is curious to know when her mother might have conceived her or if you want to know about the time of your little one’s conception, the reverse birth calculator can help.
  • The reverse conception calculator helps in planning out the date of conception for women who wish to deliver their baby at a certain month or time of the year.
  • The exact time frame of your conception can also be calculated by a reverse due date calculation by ultrasound. The time of conception can be easily calculated after the first visit to the doctor where the gestation period and due date is calculated through the last menstrual period (LMP) and the measurement of the fetus.
  • The estimated due date of delivery is calculated by considering the last menstrual period. However, this method is not accurate always since many women may not have a 28-day cycle. Therefore in such cases, the reverse conception calculator tool helps in knowing the exact time frame as to when the pregnancy began.

How Does the Reverse Due Date Prediction Method Work?

For women who know their due date, it is easy to estimate the time frame when they might have conceived. However, it is not possible to mark the exact day of ovulation since the ovulation cycle starts from the 11th day and continues until the 21st day of the monthly cycle. The reverse calendar calculator helps in getting to a time window, if not a specific day or date with a bit of mathematics. Although all you will need to do is the delivery due date to be subtracted from 266 days, the calculation can be fairly complicated. The calculation has to be done stepwise starting from subtracting the due date from 266 and then subtracting the difference with the total number of days the following month. Continue the procedure until the ninth month.

For example, if someone’s due date is 15th March, then –

  • 266 days – 15 days in March = 251 (February 28th)
  • 251- 28 days in February = 223 (January 31st)
  • 223- 31 days in January = 192 (December 31st)
  • 192-31 days in December = 161 (November 30th)
  • 161-30 days in November = 131 (October 31st)
  • 131-31 days in October = 100 (September 30th)
  • 100-30 days in September = 70 (August 31st)
  • 70-31 days in August = 39 (July 31st)
  • 39-31 days in July = 8 (June 30th)
  • 30 days in June – 8 = 22

Therefore the date of conception is the 22nd of June.

Can This Method Tell the Exact Day of Conception?

Many pregnant women question the accuracy of the reverse due date calculators and wonder if this method can tell the exact date of conception. Well, getting to the exact date of conception is a bit tricky as the period of ovulation in most women is from the 11th day to the 21st day of the monthly menstrual cycle. Moreover, most women do not monitor their ovulation cycle by keeping a track of their basal body temperature and charting their cervical mucus. For a few who do, it may not be accurate and the count can differ by a day or more.

Moreover, since sperms can live inside the body from four days to a week, one can conceive either in a few hours or in a week after intercourse. This makes it even more challenging to conclude the exact time or day of conception.

Reverse Pregnancy Calculator Limitations

Although it is a good way to get to a specific time frame of your conception, how reliable and accurate the method is, only more studies and research into it can reveal. As for now, the method has its challenges!

The accurate date of conception depends on several factors. To start, it is to be noted how the due date that is being used to know the reverse pregnancy due date has been calculated. At times, doctors or mid-wives may try to calculate using the last menstrual period which may not be accurate. In such cases where someone has to guess her LMP, the best way to know the due date is to get an ultrasound at the earliest.

Moreover, every woman does not have a 28-day cycle and therefore can ovulate earlier or later in the monthly cycle. However, it can be easy for a woman, who keeps note of the ovulation cycle and knows the exact date when they had intercourse.

If you’re pregnant and wish to know the date of conception, try out the Reverse Due Date Calculator.  And instead of just telling people your due date, you may also go ahead and let them know when your pregnancy journey started!

Also Read: 

How Accurate are Ultrasound to Predict Due Date
How to Calculate Pregnancy Due Date
How to Calculate Your Pregnancy