We distinguish between absolute, daily and weekly growth.
If not said otherwise, we use “Growth” as the average weekly growth rate of a profile. The growth rate does not compare the number of fans at the beginning and the end of a period, but it answers the question “How much had the profile to grow in a week on average to get from value A to value B?”. That makes sense, because it gives you a more “stable” impression about the growth without being too vulnerable to sudden spikes or extreme differences.
Example for weekly growth rate:
User A has 2000 followers, when two weeks ago it only had 500. Just the difference is 1500 followers or 300% of the starting value of 500. The calculation of the average weekly growth rate “only” equals to 100%. The user grew by 100% in the first week, which is 500 followers: 500 followers + 500 followers = 1000 followers. For the second week it’s another 100%: 1000 followers + 1000 followers = 2000 followers.