Our due date calculator can help determine when your baby may be born based on the date of your last period and the length of your cycle. On average, your pregnancy should last around 40 weeks, or 280 days, from your last period. (If it sounds like a long time now, just wait until you're 39 weeks pregnant.) Once you've calculated your pregnancy due date, you'll not only have a goal to focus on, but you'll be able to keep yourself healthy, monitor your baby's development, and prepare for the big day. Our due date predictor helps you figure out exactly when to expect your new baby. Whether he shows up early, late, or right on time is another question.