Leftover cooked chicken is good for around 4 to 6 days in the refrigerator before it goes bad.
If you freeze the leftover cooked chicken then the frozen cooked leftover chicken should last for 6 months or longer but it loses it's quality and freshness the longer it stays in the freezer.
In the refrigerator the leftover cooked chicken can still grow bacteria after 6 to 7 days so it's best to eat the cooked chicken before 6 to 7 days.
If it's raw chicken the raw chicken will last only 3 to 4 days in the refrigerator because the refrigerator does not keep the chicken cold enough to not spoil and grow bacteria after 4 days.
But in the freezer the raw chicken can last up to a year but it's best to cook the raw chicken within 6 months.
The longer you keep the chicken the less fresh it will be.
I have kept raw chicken frozen for as long as 14 months and it's been okay to eat.