How to Calculate Your Due Date

Step-by-Step Guide

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   Step 1: Determine the date of your last menstrual period (LMP) before you found out you were pregnant.

   This method works best for women whose menstrual cycles last around 28 days.
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   Step 2: Add 40 weeks from that date to determine the due date.

   Pregnancy usually takes 9 months, 40 weeks, or 280 days — give or take a few weeks — from the LMP. , An easier way in figuring out due dates is to take the first day of your last period, count backward 3 months, add 7 days, and add an entire year.
   
   This is called Naegele's Rule. (Alternatively, to get the same result, you can take your LMP, add 1 week, and add 9 months.) , In this case, it may be difficult to determine the due date without help.
   
   To get a more accurate measure, you may want to wait until you see the doctor and have an ultrasound to determine the baby's gestational age and your due date.
   
   You may, however be able to hit upon a rough estimate.
   
   Most women ovulate 14 days before their period begins.
   
   So if your cycles are 40 days, then you probably ovulated on the 26th day.
   
   If you know the day(s) of ovulation, just add 266 days to that date to determine a very rough estimate.
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   Step 3: Alternately

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   Step 4: remember Naegele's Rule.

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   Step 5: Choose other methods to calculate your due date if you cannot remember the date of your LMP or have irregular periods.

Detailed Guide

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