How to Calculate Due Dates

Estimated due dates are not actually counted from the date of conception, but rather 40 weeks after the first day of the last menstrual period. Most pregnancies vary anywhere from 38 to 42 weeks from the first day of the last menstrual period. Even though the due date is calculated from the last menstrual period, it is approximately two weeks after that the egg is fertilized. Very few women actually deliver on their estimated due dates. The online calculators listed in the references make it easy to calculate due dates; this article describes how to do so manually.

Things You'll Need

• Calendar

Instructions

1. Obtain a calendar.

2. Determine to the best of your knowledge the first day of your last menstrual period and mark it on the calendar.

3. Count 40 weeks from the marked date on your calendar and that is your estimated due date.

References

• Kids Health, A Week-By-Week Pregnancy Calendar, June 2008

Resources

• Women's Health, Ovulation and Due Date Calendar