A canopy tension system for an umbrella. The umbrella comprises a frame having a pole with a rib assembly at one end, the rib assembly comprising a plurality of ribs an end cap assembly attached to a distal end of each rib, the end cap assembly including a channel with an adjustable depth for receiving the rib; and a canopy attached to the end cap assembly of each rib of the frame. The end cap assemblies are adapted to modify the tension of the canopy to prevent excessive or insufficient tension when the canopy is mounted by adjusting the depth of one or more channels before the distal end of the rib is inserted.