How To Calculate Conception Without A Period

How To Calculate Conception Without A PeriodIt is not very easy to find out when exactly you have conceived. Determining the date of conception becomes very difficult if you cannot remember the date of your last period even.

However, your healthcare provider can help you in determining the date on which you conceived. There are some ways by which you can calculate the date of your conception.

Home Pregnancy Test

First you need to mark the date on which you had a positive home pregnancy test. A test will show positive results only when 13.6 days have passed from the conception date. This has been validated by many medical websites. It is estimated that your first pregnancy test date should be around 2 weeks past conception. However, please note that this is not at all a reliable test as you can be well beyond 2 weeks at the time of your test.

Size of the Uterus

A pelvic examination is required to measure the size of the uterus. The doctor might feel the abdomen or use the tape to measure it. The fundal height refers to the distance between the top of the pubic bone to the top of the uterus. This height grows by 1cm in every week of pregnancy.

But this test will give a rough idea about the gestation. A variety of factors like the amount of amniotic fluid and the position of the baby can affect a measurement. If the woman is in the 7th month of pregnancy, then measuring the fundal height will be a futile exercise.

Ultrasound Measurement

The size of the baby can be determined with the help of an ultrasound. This can be dome within three weeks of conception. The length of the baby from the head to the bottom will give an accurate estimate of the gestational age till the woman is 3 months pregnant.

But you can get the most dependable result when the woman is between 2 – 2 ½ months pregnant. In the second trimester, the ultrasound readings will give a near accurate measurement till the 22nd week of pregnancy. But when the woman enters third trimester, the ultrasound measurements will be, most likely, way off the mark.

Actual Conception Date

When you have an idea about the gestational age of the baby, calculate your conception date. Pregnancy dating considers the time from the last menstrual period. If the ultrasound measurement reveals that the baby is 8 weeks 6 days old, then it can be ascertained that the conception took place 6 weeks 6 days ago. The conception takes place when you are actually 2 weeks pregnant. In order to find out the exact date of conception you can just count back 6 weeks and 6 days on the calendar.


You must have an early check-up with your healthcare provider to get an almost accurate date of conception. The best time is always the first three months as there are minimal variations in regard to size of the fetus and the uterus. The measurements go haywire in the second trimester as the babies grow at varying rates.