Calculating on Your Own

• 1). Add seven days to the first day of your last period.
  
  
• 2). Subtract three months from the date you have from step 1. So if the date from step 1 is May 1, you would use February 1 as your starting point.
  
  
• 3). Add one year to the date you calculate in step 2. This is your estimated due date.
  
  

Using an Online Calculator

• 1). Choose an online due date calculator. (See Resources for examples of two.)
  
  
• 2). Enter the first day of your last period using the drop down menu. Some calculators allow you to enter the date of conception instead, if known.
  
  
• 3). Click "Calculate my due date." Your estimated due date and other pregnancy tips will be displayed.