This is a Plus 1 Month icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,300 icons, all in the same style and quality.
This is an icon representing plus one month. It has a calendar made up of two differently sized rectangles. There are two small rectangles on the top of the calendar where the rings would be and it has + 1m written in the center.