Which battle cost the most lives in single day?

The Battle of Stalingrad, fought between the Soviet Union and Nazi Germany during World War II, is often cited as one of the deadliest single battles in history, with significant casualties occurring over several months. However, the single deadliest day in terms of casualties is generally considered to be the first day of the Battle of Antietam, fought on September 17, 1862, during the American Civil War, where approximately 22,717 soldiers were killed, wounded, or missing. This battle marked a pivotal moment in the war and remains the bloodiest single day in American military history.