Calculating your baby's due date is so easy, you can do it yourself without the help of a doctor or other medical professionals. A simple formula, based on the date of your last menstrual cycle, is the basis for making your calculation. You can find dozens of online pregnancy due date calculators that will help you find your special day in a matter of seconds. If you want to determine your due date manually, you can do so with a few simple calculations.
Step 1
Write down the date on which your last menstrual cycle started. By the time you miss your first period, you will be four weeks pregnant.
Step 2
Add nine months and seven days to the date of the first day of your last menstrual cycle. This is your estimated due date. For example, if your last period started on January 1, move forward nine months to October 1, add seven days to get an estimated due date of October 8.
Step 3
Calculate your estimated due date backwards, subtracting three months from the first day of your last period and adding seven days. For example, using January 1 as the first day of your last menstrual cycle, go back three months to October 1, add seven days to get an estimated due date of October 8.
Step 4
Perform an Internet search using the phrase, "estimated due date," or similar words. You will get dozens of results showing websites that offer free due date calculators.
Step 5
Follow the directions on one of the due date calculators that require the first day of your last menstrual cycle. Some calculators may ask additional information, including the average length of your cycle. Use a second or third calculator to verify the results from the first.
Step 6
Discuss your calculations with your doctor. She will give you additional information about due dates, including a margin of error in days calculated and other pertinent information.
Tips and Warnings
- Because not all months have the same number of days, your estimated due date is just an estimate, and your actual delivery day may come a week or more before or after the estimated delivery date you calculate.
