How to Calculate a Conception Date

When measuring pregnancy, doctors use the date of the last menstrual period as a starting point, rather than the actual conception date. It is not always easy to calculate when conception occurred, especially if the pregnancy was not planned. Women who have regular periods every 28 days have an easier time figuring out their conception dates, because they tend to ovulate around day 14 of their cycles. Women with irregular periods do not always know when ovulation occurs, making it harder to pinpoint the exact date of conception.

Instructions

Difficulty: Easy

Things You’ll Need:

• Calendar
• Ovulation predictor kit
• Ultrasound

1. Mark your calendar when you start your period so you will have a reference point from which to start. Do this every month in order to record a pattern of how long your cycles are.
2. Listen to your body's signals to know when ovulation is imminent. Some women feel an ache in their lower backs where the ovaries are and have increased cervical mucus during ovulation. Note the date of these signs on your calendar.
3. Use ovulation predictor kits to have a good idea when ovulation occurs. The surge of the LH hormone that you see on the dipstick (either a line or a digital readout) will alert you to this fact. If pregnancy occurs during this cycle, you will know it had to happen during one of the LH-surge days.
4. Visit one of the many pregnancy calculator websites that exist. When you plug in your due date, the computer can calculate your conception date by counting backwards. The calculators tend to base their dates on a 28-day cycle, so it may be slightly off if your cycles are longer or shorter.
5. Have an ultrasound done to measure the age of your baby. As early as 5 weeks, ultrasounds can accurately date a pregnancy and allow you to calculate the date of conception. Ultrasounds are especially helpful if you do not keep track of your periods and have an unplanned pregnancy.

Tips & Warnings

• Remember, conception and due dates are just estimates. Babies will arrive when they are ready, regardless of the actual date.
• If you are undergoing fertility treatments such as in-vitro fertilization (IVF), it is much easier to determine the exact conception date. With IVF, it has to be the date the embryo was transferred into your uterus. Be sure to write these dates on your calendar to have an accurate record of your pregnancy.