Calculate % Growth and Net increase

[Muse83]

This is most likely simplistic but is giving me trouble. I'm trying to find the best way to set up a formula to help calculate the % of growth and the overall net increase from this group of numbers. I will input new numbers each month and needed it to automatically populate the data. Thank you in advance

[Cdubisms]

Are you wanting to calculate the % of grown and the net increase each month, or an overall number that changes as you add data?

[Muse83]

An overall number as I continue to add data each month

[Muse83]

Quick note. The data shown was sent to me by someone giving me an example. With that data they came up with a 0.4% overall growth and a net increase of 14. I'm unable to figure out how they came to that conclusion. Any help would be greatly appreciated. Thank you!

[MrShorty]

I'm not sure either. The overall trend in the data is downward, so I don't even see how they could get a positive value for the growth rate.

The 14 appears to simply be 0.004*3500. So, once they get the growth rate, they are simply multiplying it by one of the values or an average value or something like that.

If I assume an exponential growth/decay model [y=A*exp(r*t)] where t is the number of months since november 2015, I get an exponential decay rate of -0.004. Is that possibly what they meant?

At this point, I don't think we can really answer the question at hand until we know exactly how they are wanting to calculate these rates. If this is a homework problem, perhaps we can infer something from where this fits into the context of your coursework. Or perhaps share where this example problem is coming from.

[Muse83]

Not homework, just something I was looking at for a buddy. This is how they said in an earlier email they came up with the data I had sent earlier "The % growth for November through April was calculated by looking at net gain/loss of total members from month to month and dividing that by the 1st month’s total membership"

[MrShorty]

I'm not sure that explains the numbers they are getting. (3543-3560)/3560= -0.48%. It is easy enough to calculate that same quantity for each data point, but I don't see how that list of % gains/losses gives an overall value of 0.4%.