What if I know my conception date?

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In the survey, 35 participants claim to know their exact conception date. This is rare; most due dates are measured from last menstrual period because it's easier to track. But the general question that always comes up is "Would my due date be more accurate if based off the conception date?"

On the main probability chart I found that due dates have about an 8-10 day standard deviation, meaning that the bulk of the babies are dispersed within plus or minus 10 days of their due date.

For this graph, I subtracted each babies birth date from his or her conception date, then added 14 days across the board because that's usually what we do when calculating a due date based on conception.

The standard deviation didn't improve much when compared to all the women in the survey. So bad news... even if you know the second your baby was conceived, your due date won't be any more accurate.

There is a related chart that compares LMP due dates with ultrasound-determined due dates. It also found no noticable difference in standard deviation.

The statistics right now are as follows:

Data Table

The percentages are based on ALL births (including inductions)
DayWeekBirths Running TotalPercentRunning Total %
24535W,0D000 % 0 %
24635W,1D000 % 0 %
24735W,2D000 % 0 %
24835W,3D000 % 0 %
24935W,4D000 % 0 %
25035W,5D000 % 0 %
25135W,6D000 % 0 %
25236W,0D000 % 0 %
25336W,1D000 % 0 %
25436W,2D000 % 0 %
25536W,3D000 % 0 %
25636W,4D000 % 0 %
25736W,5D000 % 0 %
25836W,6D112.9 % 2.9 %
25937W,0D010 % 2.9 %
26037W,1D122.9 % 5.7 %
26137W,2D020 % 5.7 %
26237W,3D132.9 % 8.6 %
26337W,4D030 % 8.6 %
26437W,5D030 % 8.6 %
26537W,6D142.9 % 11.4 %
26638W,0D040 % 11.4 %
26738W,1D040 % 11.4 %
26838W,2D265.7 % 17.1 %
26938W,3D060 % 17.1 %
27038W,4D172.9 % 20 %
27138W,5D182.9 % 22.9 %
27238W,6D2105.7 % 28.6 %
27339W,0D0100 % 28.6 %
27439W,1D0100 % 28.6 %
27539W,2D0100 % 28.6 %
27639W,3D2125.7 % 34.3 %
27739W,4D1132.9 % 37.1 %
27839W,5D51814.3 % 51.4 %
27939W,6D0180 % 51.4 %
28040W,0D0180 % 51.4 %
28140W,1D1192.9 % 54.3 %
28240W,2D1202.9 % 57.1 %
28340W,3D3238.6 % 65.7 %
28440W,4D1242.9 % 68.6 %
28540W,5D0240 % 68.6 %
28640W,6D1252.9 % 71.4 %
28741W,0D3288.6 % 80 %
28841W,1D2305.7 % 85.7 %
28941W,2D2325.7 % 91.4 %
29041W,3D0320 % 91.4 %
29141W,4D0320 % 91.4 %
29241W,5D0320 % 91.4 %
29341W,6D1332.9 % 94.3 %
29442W,0D1342.9 % 97.1 %
29542W,1D1352.9 % 100 %
29642W,2D0350 % 100 %
29742W,3D0350 % 100 %
29842W,4D0350 % 100 %
29942W,5D0350 % 100 %
30042W,6D0350 % 100 %

Due Date Survey Data

Due date statistics: A study on the length of pregnancy
Probability of delivery resulting from spontaneous labor after 35 weeks
Probability of delivery within x days of a given date
Length of pregnancy by week
Spontaneous labor and due date determination
Length of pregnancy, comparing subsequent births for individual moms
Length of pregnancy for first time vs. second & third time moms
Length of pregnancy, type of delivery
Gestation vs. Birthweight
Probablity of Induction after a given day
Average day of spontaneous labor vs. age of mother at time of birth
Are more babies born during a full moon?
What's the most common day of the week for babies to be born?
I'm still pregnant at 40W. What's it mean?
Do winter babies arrive later?
What if I know my conception date?
Are boys or girls born later?
Subsequent pregnancy date search
How do inductions bias the due date statistics?
Download the data
Birth Stories
Survey input dates

More Resources

Pregnancy Day-by-Day
Fast pregnancy calendar
Baby age calendar
EDD Icon Generator
Jo's Birth Story
Weeks vs. Months Explained
Charts generated by flot
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