Backwards/ Retro Rental Calculator question

[Matt Stricklen]

Ok. Numbers people, please advise.

I'm working up a retroactive analysis on a deal, mostly to pat myself on the back but maybe also to show to later potential partners. 

In 2012 I purchased a duplex and house hacked until I moved out in year 6.

So the rent, with modest increases in the first 6 years is easy to calculate, but in year 6 it takes a big jump when I started leasing both sides instead of just 1 unit. 

So the question is, what is the best way to calculate the annual income growth as a percentage? The way the calculator is designed, that is a more or less constant rate through the lifetime of the deal, so I'm not sure how to determine that rate.

Any help is appreciated.