Turning my house into a rental. How do i calc cost for ROI?

[Bryce McBride]

I'm very new to learning about real estate, and have some questions. I'll have more after this but my other questions could change based on the answers i get. I'll admit, they may be stupid, it scares me enough that i want a very detailed introduction book that tells me everything to do. I know that it won't happen and would be impossible as we are all different.

Anyway, I bought my house 6 years ago and got a really good deal. Now, having learned about real estate, I really want to put it up for rent. I have probably put $12,000 into it since living here. How would you this calculate the return on investment when the time comes to rent it out? Would you use what i spent over the years in mortgage payments? Would you add cost to repairs that I've done? Or would you simply say that on the day i move out and make it a rental property, then all repairs/costs get counted in my calculations?