There is no shortage of real estate and mortgage calculators on the web. Almost all are pretty simple, but they do a decent job of giving you a general estimate of what to expect given a certain set of assumptions. Some time ago, I came across the most comprehensive real estate investment calculator I have ever seen. I think I found it via Clifford of Changing My Direction, but I'm not 100% sure.
This calculator not only takes into account standard data such as purchase price, down payment, loan interest rate and length, taxes, and insurance, but is also figures out the effect the investment will have on your taxes, including depreciation, income, etc. The calculator outputs data for the first 10 years of your investment. It's pretty impressive.
As with any analysis tool, the results are only as good as the data you put in. I put in what I think are fairly conservative values for an analysis of my Rental #1 property. Some of the data I used were: 3% annual income increase (default is 5%), and 3% annual appreciation rate (5% is default). I used a maintenance rate of 5% of income - my previous calculations used a fixed dollar amount which worked out to about 2.7% of income. I also said I'd put in $5,000 of capital improvements above and beyond the maintenance amount.
According to the calculator, my return on my initial equity (down payment plus capital improvements) is 21.50% my first year, 22.55% my second year, and increasing to 32.22% by year 10.
The calculator also shows your return on total equity, which takes into account appreciation and your decreasing loan balance. This is really nice because this value will actually decline each year since your equity is rising faster than your investment income increases. My return on total equity starts out at 21.50% and by year 10 drops to 12.54%. This is a great piece of information to have. You can see very easily where the property drops belong your minimum ROI you want an investment to have. At that point, you can sell the property or refinance the loan to take more money out.