We show two months at the same time to make it easier to navigate through time. Showing only one month at a time makes it feel very claustrophobic.

Allowing for manual input just creates a lot of questions in the users mind around which date format the date should be entered in. It also takes more cognitive energy to figure out what number corresponds to what month and the whole thing is prone to user error. If you do need to allow for the manual entry of a date (in the case of a date really far in the past such as birthday) we have the date input as covered in a previous post.

A good date selector needs to be very flexible and customizable. Date pickers are notoriously bad because it is a very difficult problem to solve. I want to change that by ensuring great usability is maintained while allowing for a variety of use cases.