Ground beef that is defrosted or thawed out will last up to 3 to 4 days in the refrigerator as long as it's been kept refrigerated when not using it.
If you want to keep the ground beef longer than 3 days you should really freeze it instead and if kept properly frozen the ground beef will easily last from 6 months to a year or more.
I sometimes buy ground beef on sale in larger quantities and then bring it home and freeze it.
Although the ground beef loses it's freshness after 6 months of being frozen the ground beef is still very safe to eat and I use the ground beef in stews and soups a lot.
I never keep thawed ground beef longer than 3 days in the refrigerator and if I plan to keep the ground beef longer than 3 days then it goes in the freezer instead.