Abstract: An adjustable bracket device for selectively mounting on buildings a plurality of rain gutters of different sizes and shapes, includes a base having an elongate mounting member and an integral arm member projecting outwardly therefrom. An extension member is attachable to the arm member in multiple overlapping relationships forming the assembled arm and extension members of differing collective lengths. The base is disposed within a selected gutter in a substantially vertical orientation with the mounting member abutted against the back wall of the gutter and is secured to a vertical building wall via a fastener penetrated through mounting member and through the back wall of the gutter. The collective overlapping length of the arm and extension members is selected to conform to the width of the selected gutter to extend laterally across the full channel width of the gutter into supporting engagement with the front wall of the gutter.