Calculating Due Date or conception Date

Use the Pregnancy Conception Calculator for calculating due date or conception date to estimate your baby's arrival. Remember that a due date is a rough estimate at best:  only about 1% of all babies are born on their due dates.

Pregnancies are considered to be full-term after 37 weeks.  However, the average length of a first time pregnancy worldwide is 41 weeks, 1 day, and many go to 42 weeks, so there is a wide range in which to anticipate the baby's arrival.  First pregnancies are usually a bit longer than subsequent pregnancies.  To avoid feeling pressured if your due date passes, some women prefer to refer to their due month rather than a specific day.

Last Menstrual Period: 
(MM/DD/YYYY format)
Average Length of Cycles: (22 to 45)
(defaults to 28)
Average Luteal Phase Length: (9 to 16)
(defaults to 14)

Estimated Conception:
Estimated Due Date:
Estimated Fetal Age:

Understanding the Pregnancy Due Date Calculator

Last Menstrual Period: Enter the first day of your last period.

Average Length of Cycles: This is the usual length of your cycle from the first day of your period to the day before your next begins.  The average is 28 days; however, significantly longer or shorter cycles will increase or decrease your due date.  If you are unsure, use the default setting of 28 days.

Average Luteal Phase Length: This is the interval after ovulation to the beginning of your next period.  If you do not track your cycles through BBT or ovulation predictors, you may not know your luteal phase length.   The average luteal phase length is 14 days but the normal range is between 11-16 days.

The Pregnancy Due Date Calculator is useful for calculating due dates and conception dates as well as fetal age. The conception date  is the day before your luteal phase begins. The estimated due date is the rough estimate of when to expect your baby. The last value, the estimated fetal age,  indicates the developmental level of your baby.  Remember when calculating due date or conception date, these are estimates.  Your baby will arrive in its own time.  Good things come to those who wait...

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Page Last Modified by Catherine Beier, MS, CBE

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