You’ve taken the test, anxiously awaited the results, and then you see it…. TWO lines, you’re pregnant!! Whether you find yourself jumping with joy or a bit shocked, it’s a surreal moment. Once it sinks in, many thoughts may flood in, but one of the first things you may wonder is when will your baby be due. Several apps can help you calculate that by inputting the first day of your last period. Most pregnancies last around 40 weeks from the first day of your last period or 38 weeks from conception.