Fair rental value for co-owner living in a partnership-owned home

[J. Scicchitano]

I have a real estate partnership with a family member. In late 2015, we purchase a duplex together. I put up the cash and he has done all repair and maintenance work. We are trying to determine fair value of our respective investments to calculate our ownership stakes. 

I have lived in one half of duplex since purchase. Other half rents for $1300/month. What is the fair amount that should be credited back to the partnership in exchange for the benefit of living in the house? 

Not sure if it should be market value, or I should have some discount from market value?