We've often had the scripture "the little one will become a thousand, small one a mighty nation" applied to the modern-day organization...........often represented as an amazing fulfillment of Bible prophecy.
Actually anything with a growth rate will increase exponentially in time. (It's easy to figure out with natural logarithms)
Looking back at some previous years, there was some exceptional growth, resulting in large increases every ten years or less.
Example- with a growth rate of 10% per year the total would double in about 7 years...(log 2/ .10 = .693)
With the current rate of 2% , the number of Witnesses worldwide will be doubled in (log 2/ .02= 34.65) almost 35 years.
Years ago there were some amazing rates achieved (ex. over 13% in 1975), but I doubt that will happen again.
Looking ahead, if the growth rate remains approx. the same, there should be in 20 years roughly ..........
6,500,000 * (1+.02/1)20 = 6,500,000 * 1.48 = 9,620,000
Of course, only time will tell what will happen..........if trends continue there could very well be negative growth in a few years, like what is happening in many countries, and maybe the 7,000,000 mark will never be achieved.