I dont really understand some of the other reviews. This app works perfectly well and is exactly what you would expect if you actually read the book or had a clue about what the point of it is. Of course this app is for babies AFTER they are born! DUH...so dont listen to the review of the person who says not to bother buying it if your kid is already born because they obviously havent got a clue.
The purpose of this app (which is just a simplified version of the book, btw) is to help you track their progress so that you understand how and what is happening and why with your kids cognitive and physical development. It provides insight into behavioural and mood changes and helps you to guide your child through them, which eases frustration for both of you.
The reason that it asks for your due date is because thats the point where it starts mapping your childs brain development from for accuracy sake because some babies are born in a variety of ways from planned c-sections to inductions to complete natural births so the actual birth day is less relevant than the point where the child is considered full term. Some babies are late, some are early and some are premature so you cant go by birth date. The Wonder Weeks is about brain development for babies AFTER they born, so it makes sense that to have a date to work from that is full term for continuity.
People who clearly havent read the book shouldnt write reviews for the app that goes with the book. I encourage you to read the book first, which you can get on kindle for $7 on Amazon, which Apple has an app for. If you dont have time to read the book, thats fine...this app, as Ive said is a simplified version, but if you find that you cant understand it then dont blame the app...its your fault for not reading the book!