Calculating Your Approximate Conception Date

Conception Date

If you have been trying to get pregnant, you may want to know your exact conception date. While it may be desirable to know, the time of conception is actually fairly hard to pin down. Not knowing it, however, will not affect how you determine your baby's gestational age or due date.

What Is Conception?

Conception is defined as the inception of pregnancy, or the exact moment when an egg is fertilized. Logically, it seems like your conception date and intercourse date would be the same. That may be the case, but since sperm can live inside a woman's body for up to three days, conception can happen three days after intercourse, depending on when you ovulate.

At this time medical technology has no way of pin pointing your exact conception date; it is almost always unknown. Conception must occur within 24 hours after ovulation when you release an egg for fertilization. If you have undergone artificial insemination or in vitro fertilization, however, you do know when conception occurred.

Determining Your Conception Date

While you may not be able to pin down exactly when conception occurred with complete accuracy, there are a few methods you can use to help you figure it out. All it takes is a little research and knowledge about your body.

Calculating Conception Based on Ovulation

You cannot conceive until you ovulate, so if you have been charting your ovulation date, you may be able to estimate when conception occurred. If you have a regular 28-day cycle, conception usually occurs about two weeks after the first day of your last period. For example, if your period started on October 11th, conception would occur around October 25th.

Determining When You Ovulate

Many women do not have an exact 28-day cycle and do not ovulate 14 days after the first day of their last period. If you have been charting your cycle and know how many days between periods, you should be able to determine ovulation. If your cycle is longer than 28 days, take the number 14 and add an additional day for each day your cycle is longer than 28 days.

  • If you have a 30-day cycle, you ovulated about 16 days after the first day of your last period.
  • If you have a 35-day cycle, you ovulated about 20 days after the first day of your last period.

If your cycle is less than 28 days, take the number 14 and subtract a day for each day your cycle is shorter than 28 days.

  • If you have a 24-day cycle, you ovulated about 10 days after first day of your last period.
  • If you have a 26-day cycle, you ovulated about 12 days after the first day of your last period.

Getting an Ultrasound

An ultrasound may be able to tell you the date of conception within one week based on gestational age. If you know or suspect your conception date, you may notice that it doesn't match up with how many weeks along you are. That is because gestational age is measured not by conception date, but by the date of your last period. So if you have a regular cycle and are 6 weeks along, your baby is only 4 weeks old.

An ultrasound technician can measure your baby's size and use these measurements to give you a fairly accurate measurement of when you conceived.

Signs of Conception

Unfortunately, there are no signs of conception on your conception date. You may suspect you are pregnant, especially if you have been following your ovulation cycle and trying to get pregnant.

About two weeks after you conceive, if you have a regular cycle, you may notice early pregnancy signs. These include a missed period, breast tenderness, increased urination, nausea, sensitivity to foods or smells, exhaustion and mood swings. However, many women experience few early pregnancy symptoms. If you are uncertain whether or not you are pregnant, take a home pregnancy test.

Understanding Conception

While it may be fun to determine your conception date in order to know the exact moment your baby began to grow, knowing it is not medically necessary. Your due date is typically determined from the first day of your last menstrual cycle and is only an estimate of when the baby will be born. Understanding when conception may occur can help you in your quest to become pregnant, but will not affect the outcome of your pregnancy.

Calculating Your Approximate Conception Date