How to Calculate Conception Date from Ultrasound & Due Date


How can I calculate conception date? Is it possible to estimate conception date? Find out how to calculate conception date from due date, conception date from ultrasound and calculating conception date using a pregnancy calculator in this piece.

Calculating conception date for most women is baffling even for me. The situation gets worse because of our curiosity. We want to know when exactly as if it will make any difference. The babies are already in our lives why keep going backwards. Estimating conception date is however, necessary for those of us who had sex with different partners in the same week. It gives you a peace of mind knowing who exactly your baby’s father is.

How to Calculate Conception Date from Ultrasound
How to Calculate Conception Date from Ultrasound

On the other hand, if you have sex with different lovers on a single day or night, you would have to take a paternity test.  There is no shortcut by knowing the conception date. The good thing is that only a single sperm fertilizes an egg, and with a paternity test, you can never go wrong on who exactly is the father.

The conception date in such circumstances becomes just that.  Find out conception date from due date, ultrasound, and pregnancy calculator by reading this whole piece. You will be glad to know when the day you were most fertile in the month you conceived.

How to Figure Out Conception Date

Figuring out conception date takes estimating. This because unless you got pregnant through artificial insemination or vitro fertilization, there is no telling the exact day you conceived. These methods are used when a woman is ovulating so they never fail and are spot on.  Nevertheless, if you have sex with your partner you will need to know how to figure out conception date. The truth of the matter is that conception dates are mere estimates because of the following reasons:

  • Women do not go through the same cycles of 28 days.  Some take 30, 24 or even longer days.
  • A strong sperm can survive in the vagina for a maximum of seven days.
  • An egg seeking to be fertilized can only last for 12 -24 hours, therefore calculating conception date may be missed by a single day.
  • Spotting experienced during implantation may be confused for a missed period. As such, the estimate conception date may be off by a whole month.
  • Every days stressors may cause a regular menstrual cycle to be irregular

In spite of conception dates being estimates, you can figure out conception date if you:

  • Know the chart of you menstrual cycle
  • Have been keeping record of your basal body temperature, this temperatures marks the luteal phase. This is a stage after ovulation, which is marked by high temperatures.  This day remains the same both in regular and irregular cycles.
  • Know you first day of the your last menses
  • Go for an ultrasound
  • You can also find out conception date using a pregnancy calculator online.

How to Calculate Conception Date from Due Date

Once you have the above basics on how to calculate conception date, your obstetrician will figure out the due date. Again, this is only an estimated date. The gestation period of a normal pregnancy is expected to be 280 days, 40 weeks or 10 months. You will notice it is not 9 months. This is because there is an allowance of two weeks (14 days), of when you probably conceived.  The 280 days figure assumes that you conceived from the first day of your last menses.

How to calculate conception date from due date is quite easy. A bit laborious, but worth it for any woman who wants to know the day she was most fertile. Once a healthcare professional gives you the due date, subtract the 14-days of conception from the full gestation period of 280 days.

In essence, it will be: 280 – 14 = 266

Now 266 days amount to 38 weeks. You are supposed to reverse back on the calendar for 38 weeks or 266 days if you like, from your due date until you land on the estimate conception date.  You can only subtract 14 days if you have a regular cycle of 28 days.

How to Calculate Conception Date from Due Date
How to Calculate Conception Date from Due Date

Alternatively, if you cycle is longer, say 30 days you would have to subtract 16 days instead of 14. A shorter cycle of 24 days would require that you subtract 10 days. Notice whichever way you follow, the difference is still 14 days. The 16th 14th and 10th are just the actual dates anyone on different cycles of 30, 28, and 24 respectively would have ovulated to be able to conceive.

Calculate Conception Date from Ultrasound

Another way to estimate conception date is using the ultrasound. In order to calculate conception date from ultrasound you will need to visit a radiologist in your first trimester. This is when you are about 8 to 20 weeks in pregnancy. If you want to know conception date from ultrasound, it is best to go as early as possible.

This is because if you take longer, the accurateness of the ultrasound may be diminished.  In later stages, than first trimester, the fetus has varied growth and it becomes difficult to determine its gestational age.

Fetus gestational age is from your first day of your previous menstrual period. The crown rump dating method used by the radiologists determines this gestational age. Once you have been given the gestational age, you should subtract 14 days, (2 Weeks). You will count backwards on the calendar from the date of the ultrasound to find out the estimate conception date.

Pregnancy Calculator for Conception Date

All the subtractions and additions can be too much for a pregnant woman who does not want to put her mind to test. Instead, therefore, you can use a pregnancy calculator conception date. The calculators are available online and they allow you to find your estimate conception date without sweating.

All you need is to know your menstrual cycle days, your due date, or your first day of your last period. These details are required by most online pregnancy calculators of conception and with a push of a button, your possible dates of conception and probable date of ovulation are availed. Wishing you all the best in learning how to calculate conception date!

More on Conception:

Read More on Pregnancy Signs and Ovulation.