Calculating Your Approximate Conception Date

Reviewed by RDMS Julie Kirk
Pregnancy test showing positive result and calendar

If you are trying to get pregnant, you may want to know when you will potentially conceive. It may be difficult to determine precisely when ovulation will occur, but there are ways that can help you figure out an approximate conception date.

What Is a Conception Date?

What does "conception date" mean? 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 the day you have intercourse would be the same. That may be the case, but since sperm can live inside a woman's body for up to five days, conception can happen up to five days after intercourse as well, depending on when you ovulate.

At this time, medical technology has no way of pinpointing your exact conception date; it is almost always unknown. However, once the egg is released, its lifespan is only 12 to 24 hours, therefore conception must occur within 24 hours after ovulation. If you have undergone artificial insemination or in vitro fertilization, however, you will know when conception occurred.

Determining Your Conception Date

While you may not be able to pin down exactly when conception happened with complete accuracy, there are a few methods you can use to help you figure out the conception date. 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 cycles and ovulation, you may be able to estimate when conception potentially occurred. If you have a regular 28-day cycle, ovulation usually occurs about two weeks after the first day of your last period. For example, if your period started on October 11th, ovulation would occur around October 25th. This would be the likely timeframe for conception as well.

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 cycles 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 21 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 the 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 the gestational age of the baby. A sonographer will measure your baby which will calculate the gestational age and confirm a due date. An ultrasound is most accurate when performed early in pregnancy. Once you have a gestational age for your baby, a conception date can be determined from there.

However, if you know your approximate conception date, you may notice that it doesn't match up with how many weeks you believe you are. That is because gestational age is measured not by conception date, but by the first day of your last period. So if you have a regular cycle and are 6 weeks along, your baby is actually 4 weeks gestational age.

Signs of Conception

Unfortunately, there are no true, telltale signs of conception if you've actually conceived. You may suspect you are pregnant, especially if you have been following your ovulation cycle and actively 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, some women may experience a number of early pregnancy symptoms while others experience few to none. 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, it is not information that your doctor typically needs or uses. Your due date is determined by the first day of your last menstrual period and is only an estimate of when the baby will be born. An ultrasound will help confirm the anticipated due date.

Therefore, it is beneficial for you to become knowledgeable about your body and understand and track your cycles especially if you are trying to get pregnant. Not only will you have a better understanding of your body, you may find yourself with a positive pregnancy test.

Calculating Your Approximate Conception Date