Cooked beef will last for up to 4 days in the fridge.
So make sure you eat the cooked beef within 4 days of refrigerating it otherwise it goes bad and then starts to smell and grow bacteria on it.
After 4 days in the refrigerator the cooked beef should be thrown out to prevent food poisoning.
If you want to keep the cooked beef longer than 4 days you should freeze the cooked beef instead.
When you freeze the cooked beef it will last for up to 6 months to a year when frozen as the freezing temperatures keep the bacteria from growing on the beef.
The cooked beef loses it's quality and freshness after a few months in the freezer but it's still safe to eat after that time.