How Do You Calculate the Exact Day You Get Pregnant?

Medically Reviewed on 1/14/2022
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Calculating the exact date you will get pregnant is not easy; however, understanding your “fertile window” can help narrow down your conception period.

Calculating the exact day when you will get pregnant is not easy, especially if you have irregular cycles.

  • A woman gets pregnant when a male sperm merges with an egg (ovum) released before ovulation.
  • Typically, sperm may stay alive in a woman for five days, and fertilization with the ovum may occur if it is released within these days.

The period when a woman is most likely to conceive is called the “fertile window,” which may help narrow down the conception period.

There are two ways to determine the day of conception, but these do not provide the exact date:

  1. Abdominal ultrasound:
    • It may help determine the gestational age (length of pregnancy from the first day of the last menstrual period).
    • It provides reasonably accurate information regarding the gestational age during the 8th and 18th weeks.
  2. Ovulation calculator:
    • It provides you with information about your most fertile period throughout your menstrual cycle.
    • Knowing the fertile window may give you a glimpse of the date of conception. A fertile window is five days before ovulation.
    • Ovulation (release of an egg) occurs exactly 14 days before the first day of the present menstrual cycle—the day bleeding starts.
    • If you know the length of your menstrual cycle, then you can calculate the day of ovulation. For example, if your cycles last for 28 days, the day of ovulation is the 14th day after the first day of bleeding of the previous cycle or 14 days before the first day of bleeding of the present cycle.
    • Knowing your ovulation date may help determine the date when you will get pregnant. Determining your ovulation date may be more challenging because of unpredictable or irregular menstrual cycles.

Ovulation calculator

How to use this ovulation calculator tool

  • Pick a date on the calendar that matches the day you started your last period
  • The calendar will display your estimated ovulation date, marking it in red.
  • The days leading up to your ovulation date will appear marked in purple; those are the days you are likely the most fertile.
  • If you have records of how long your menstrual cycle lasts, change the default number of 28 days in the dropdown menu in the results box for a more accurate calculation.

What is the date of conception?

Conception usually occurs 11 to 21 days following the first day of the previous period in a woman who has regular menstruation.

Most women do not know the precise day of conception because it is difficult to predict when ovulation will occur. Hence, their conception date is only an educated guess based on the first day of their last period.

What is the gestational age?

The gestation period is the time between conception and birth. The fetus grows and develops inside the mother's womb throughout this time.

During pregnancy, gestational age is a word frequently used to express how far along the pregnancy is. It is measured in weeks, beginning with the first day of the woman's previous menstrual cycle and ending with the present date.

A typical pregnancy can last between 38 and 42 weeks.

  • Premature babies are those born before 37 weeks.
  • Postmature infants are those born after 42 weeks.


Stages of Pregnancy: Week by Week See Slideshow

What is EDD?

The estimated date of delivery (EDD) is the day on which spontaneous labor is expected to begin. To estimate the due date, add 280 days (nine months and seven days) to the starting day of the last menstrual cycle (LMP).

The accuracy of EDD calculated by this approach is dependent on the mother's accurate recollection, of the number of days of her menstrual cycle and ovulation and conception occurring on day 14 of the cycle.

The use of LMP to determine the due date may overestimate the length of the pregnancy by more than two weeks.

Check out the pregnancy due date calculator below:

What is a menstrual cycle?

Menstrual cycle is the sequence of events that take place within a woman's body each month as her body prepares for potential conception. It is the number of days from the first day of bleeding from one period to another, and it usually ranges from 25 to 35 days (a normal cycle is of 28 days).

The menstrual cycle is due to changes in hormonal levels at different times of the month.

At different stages of the menstrual cycle, the pituitary gland in the brain and ovaries in the female reproductive tract produce and release hormones that drive the reproductive organs to behave in certain ways.

Different phases of a menstrual cycle include:

  • Menses phase: This phase normally lasts from day one to day five.
    • The endometrium (uterine lining) is shed through the vagina if pregnancy has not occurred during this phase.
    • Most women bleed for three to five days although a period that lasts two to seven days is still considered normal.
  • Follicular phase: This stage usually lasts for 6 to 14 days.
    • During this period, the amount of the hormone estrogen increases, causing the endometrium to expand and thicken.
    • Furthermore, another hormone (follicle-stimulating hormone) stimulates the growth of follicles in the ovaries.
    • One of the growing follicles will produce a completely developed egg between days 10 and 14.
  • Ovulation: This phase occurs on day 14 of a 28-day menstrual cycle.
    • The ovary releases its egg when there is a rapid surge in another hormone: the luteinizing hormone. This is known as ovulation.
  • Luteal phase: This phase lasts for about 14 days (or up to 20 days in some women) and ends on day 28.
    • After the egg is released from the ovary, it travels to the uterus through the fallopian tubes.
    • Progesterone levels increase to aid in the preparation of the uterine lining for pregnancy. The woman becomes pregnant if the egg is fertilized by a sperm and attaches itself to the uterine wall.
    • If there is no pregnancy, estrogen and progesterone levels decrease, and the thicker uterine lining is shed during the menstrual cycle.

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Medically Reviewed on 1/14/2022
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