How many years was the US involed in World War 2?

the us entered the war in 1941 after the Japanese bombed pearl harbor until the end of the war 1945.
The U.S. was in WWII from December 8, 1941 (when FDR signed the declaration of war against Japan, and 4 days later Germany declared war on the U.S.) until September 2, 1945 (when Japan signed the Japanese Instrument of Surrender on board the USS Missouri).