How to determine CoC return on rental of my primary residence.

[Chris Robinson]

I am brand new to the world of real estate investing and and am not sure how to calcuate the CoC return if i decide to rent out my primary residence. If I were simply purchasing an investment property I would calculate the CoC based on annual cashflow / total investment. Since I bought my primary residence about 3 years ago without any thought of using it as an investment property, do i still add my down payment and closing costs from the purchase 3 years ago into any calculation for my total investment? Or would I simply consider any new potential investment into the house from this point forward into my calculations.

TIA