Cooked ground beef can last from 4 to 7 days in the refrigerator before it goes bad.
However after 4 days in the refrigerator the cooked ground beef will begin losing it's freshness and start to go stale so it's best to eat the leftover cooked ground beef within 4 days for the freshest taste.
If you want to keep the cooked ground bee longer than 4 days I would recommend freezing it instead and when frozen the cooked ground beef will last for up to 4 months before it goes bad.
I always freeze any leftover cooked food that contains ground beef or any leftover cooked ground beef itself to keep it longer than 4 day because it stays fresher longer and lasts longer.