What is a healthy rate to lose or gain weight

A healthy rate to gain or lose weight is 1 lbs to 2 lbs a week(less than 2 lbs per week).

So if you need 3000 calories per day to maintain your current weight and you want to lose weight at a rate of 1 pound a week,you have to eat 2500 calories per day.

If you want to lose weight at a rate of 2 pounds a week,you have to eat 2000 calories per day.

Related:
How Many Calories Should I Eat
How many calories is the minimum per day
How many calories does it take to lose one pound