This is the Calendar 1 icon for Windows 10. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.
It's a square with two ring-like objects attached to the top, to indicate that this is a calendar that would flip to change the date each day. Inside the square is the number 1, to signify the 1st day of the month.