It's hard to add calendar on a wallpaper.
So, I just made an app <Add Calendar> which adds a calendar on your wallpaper.
It's so simple, just follow me only for a second.
1. Choose a picture you want.
2. Set a area you want by cropping and moving the picture.
(Football icon on the top provides a football schedule.)
3. Create your own calendar.
4. Check whether the calendar fits your wallpaper or not.
If not, modify the design of the calendar again.
5. Save it to <Photos>, and use it as a wallpaper.