Abstract: In order to form a chamfer on an outside corner of a poured concrete structure, a concrete forming system includes a first form panel having an inwardly facing surface and second form panel also having an inwardly facing surface. The first form panel is secured to the second form panel with the inwardly facing surfaces at an angle to one another and the inwardly facing surfaces of the form panels have adjacent side edges for forming an outside corner. A chamfer strip including a body portion and a tail portion is provided for forming a chamfer on the outside corner. The body portion is substantially hollow and has three sides arranged so as to be generally triangular in shape and the tail portion comprises an elongated continuation of one of the sides of the body portion. With this understanding of the concrete forming system, the chamfer strip is formed in such a manner as to permit flexing of the chamfer strip so as to create a seal with the form panels during the pouring of concrete.