pregnancy calculator
A full-term pregnancy is 280 days, which is 40 weeks in duration; however, not every woman gives birth at the 40th week.

A full-term pregnancy is 280 days, which is 40 weeks in duration. With four weeks a month, a 40-week duration could be calculated as 10 months where each month has 28 days; however, days in months vary, which range from 28 to 31 days long.

Therefore, pregnancy typically carries on for nine and a half months.

  • Not everyone delivers at the 40th week, and women may give birth at about 38 to 42 weeks.
  • In the case of a single baby, the mother may deliver at 39 to 40 weeks, and in the case of twins, the delivery generally occurs at about 38 weeks.

Generally, it is said that a pregnancy lasts for nine months.

How is the due date calculated?

The due date or the estimated date of delivery (EDD) is the day when spontaneous labor is expected to start. To calculate the due date, add 280 days (nine months and seven days) to the starting day of the last menstrual cycle (LMP).

  • This is the strategy employed by "pregnancy wheels."
  • The accuracy of the EDD determined by this method is dependent on the mother's exact recall of the number of days in her menstrual cycle, as well as ovulation and conception happening on day 14 of the cycle.
  • The use of LMP may overestimate the length of the pregnancy by more than two weeks when used to calculate the due date.

The doctor may tell a person’s approximate due date based on physical examination and ultrasound findings.

Pregnancy due date calculator

How to use the Pregnancy Due Date Calculator

  • Select the date of the first day of your last menstrual period in the space provided.
  • Select your average menstrual cycle length from the dropdown menu.
  • Your due date, the gestational age (age from conception to birth) of your baby, and a trimester timeline will appear in the window next to the calculator.
  • Click reset to start over.

What are trimesters?

A full-term pregnancy of 40 weeks is divided into three trimesters with each trimester consisting of three months in duration.

First trimester

The first trimester is called early pregnancy that lasts from the 1st to 13th week.

  • First month
    • One to four weeks of pregnancy.
    • During the first and second weeks of the first trimester, the egg released by the female will be fertilized by the sperms that enter the uterus following unprotected vaginal sex.
    • During the third and fourth weeks, the fertilized egg moves down the fallopian tubes and reaches the uterus. During this stage, the single cell in the egg starts to divide to form multiple cells, which is called an embryo.
    • Not all embryos implant to form a fetus. Sometimes, the menstruation process may begin, the fertilized egg may not be able to get implanted and it is released out.
  • Second month
    • 5th to 8th weeks of pregnancy.
    • At 5 to 6 weeks, the implanted embryo grows to 4 to 5 mm long and starts developing the following:
      • The circulatory system
      • Simple beating heart
      • Buds to form the arms and legs
      • Bud of a tail grows
      • The neural tube develops that will eventually give rise to the brain, spinal cord, and main nerves
      • Umbilical cord begins to form
    • At 7 to 8 weeks, the embryo is 7 to 14 mm long and forms:
      • The heart
      • Webbed fingers and toes
      • Arms are bent at the elbows
      • Facial structures, such as ears, eyes, eyelids, and upper lip develop
      • Liver is developed
      • Differentiation of sex begins during this time
  • Third month
    • 9th to 13th weeks of pregnancy.
    • At 9 to 10 weeks:
      • The embryo develops into a fetus and grows up to 21 to 40 mm long
      • Tail disappears at this time of development
      • Toes and fingers grow
      • The placenta is developed and is attached to the uterus to get nutrients
      • The abdomen of the fetus and placenta are connected by the umbilical cord
      • The umbilical cord provides the fetus with nutrients and oxygen and carries away waste products from the fetus
    • At 11 to 12 weeks, the fetus can be measured from the head to the buttocks, which is called crown-rump length (CRL):
      • The CRL is two to three inches
      • Bones get stronger
      • Webbing of toes and fingers is no longer seen
      • Fingernails grow big, and the skin develops
      • External sex organs begin to develop under the influence of hormones
      • Fetus moves spontaneously
      • Kidneys begin to filter blood and form urine
      • Eyelids fuse
      • Sweat glands appear

Second trimester

The second trimester is called mid-pregnancy and lasts from the 14th to the 27th week.

  • Fourth month
    • 14th to 17th weeks of pregnancy.
    • By the end of the 13th week and beginning of the 14th week, the fetus undergoes the following developments:
      • The crown-rump length (CRL) is about three inches
      • The biological sex of the fetus can be determined by looking at the external sex organs
      • In biological males, the development of the prostate gland begins
      • In biological females, the ovaries descent from the abdomen to the pelvic area
      • Hair starts growing
      • The roof of the mouth is developed
    • At 15 to 16 weeks:
      • The CRL is about 4.5 inches
      • Millions of eggs form in the ovaries if the fetus is biologically female
  • Fifth month
    • 18th to 22nd weeks of pregnancy.
    • By the end of the 17th week and the beginning of the 18th week, the fetus has a CRL of 5.5 to 6 inches.
    • At 19 to 20 weeks:
      • The CRL is 6.5 inches
      • The body is covered with fine hair
      • The skin is covered by a protective greasy material called vernix caseosa
      • Biological females develop a uterus
    • At 21 to 22 weeks:
      • The fetus CRL is about 7 inches
      • Blood cells are developed from the bone marrow
      • Taste buds start developing
  • Sixth month
    • 23rd to 27th weeks of pregnancy.
    • At 23 to 24 weeks:
      • The fetus CRL is about 8 inches
    • At 25 to 26 weeks:
      • The fetus CRL is about 9 inches
      • The development of fat increases in the fetus, and it keeps on developing until the pregnancy ends
      • Eyelashes and eyebrows are developed in 23 to 26 weeks

Third trimester

The third trimester is called late pregnancy and is the 28th to 40th week or until the delivery of the baby.

  • Seventh month
    • 28th to 31st weeks of pregnancy.
    • By the end of the 27th week and beginning of the 28th week, the fetus has:
      • The crown-rump length (CRL) of about 10 inches
      • Eyelids remain fused until 28 weeks
    • At 29 to 30 weeks:
      • The CRL of the fetus is 10.5 inches
      • The testis starts to descend into the scrotum from the abdomen in biological males, and the process completes at the 40th week
    • At 31 to 32 weeks:
      • The CRL of the fetus is about 11 inches
      • The soft baby hair called lanugo starts to shed off
  • Eighth month
    • 32nd to 35th weeks of pregnancy.
    • At 33 to 34 weeks:
      • The CRL of the fetus is about 12 inches
      • Development of pupils has reached to an extent that they can constrict and dilate with response to light
      • The lanugo is completely lost
  • Ninth month
    • 36th to 40th weeks of pregnancy.
    • By the end of the 35th week and beginning of the 36th week:
      • The CRL of the fetus is about 12.5 inches
      • The skin tightens wrinkles do not appear, and the fetus becomes bulkier due to fat deposition
    • At 37 to 38 weeks:
      • The CRL of the fetus is about 13 to 14 inches
      • The fetus develops a firm grip
    • At 39 to 40 weeks the mother delivers the fetus:
      • The newborn may weigh up to seven to eight pounds and range from 18 to 22 inches long with open legs
      • The lanugo and vernix are completely gone
      • If the fetus is born with lanugo, it may disappear within a few months

SLIDESHOW

16 Early Signs & Symptoms of Pregnancy: Could You Be Pregnant? See Slideshow

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Medically Reviewed on 1/21/2022
References
Image Source: Getty Images

Marple K. Pregnancy in weeks, months, and trimesters. BabyCenter. https://www.babycenter.com/0_how-pregnant-am-i-pregnancy-by-weeks-months-and-trimesters_10326878.bc

Hunterdon Healthcare. Pregnancy Month by Month. https://www.hunterdonhealthcare.org/service/maternity/pregnancy-month-by-month/