This is the Plus jeden dzień 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.
The icon is depicting a calendar that is rectangular with sharp edges and a line dividing the top portion from the bottom. In the center of the object is written plus one 'd' indicating plus one day on the calendar.