Where can I find an ROI calculator for Real Estate?

[theblitz]

I am considering investing in a property and am looking for a calculator that will give me an accurate value of my ROI in different situations.
I want to get a property such that the rental covers the mortgage (I have money fro the down payment).
So, I would like to be able to calculate if the yearly ROI is better when I buy a smaller property with a shorter repayment time or a larger one with a longer repayment time.

Can anyone help?

[RikaKazak]

Are you looking at cap rate? Or like assuming "x" appreciation and looking for ROI on initial investment?

I'm confused.

I never use a calc, always do it by hand, that way I get a good "feeling" for my investments.