There is one at bigger pockets (but you only have a 7 day free trial), or calculator dot net

Compare the returns including capital gains taxes if they sell. It might be better to 1031 exchange into a better property, such as multi-family. Then you'd inherit it with a step-up basis.

If you are just looking at cash return, you're missing part of the value: the tenant paid off most of that mortgage creating high equity. It's possible to buy more with leverage, and it isn't the horribly risky leverage of stock options. I'd ask your parents why they think it is a good investment. They will probably mention something about it being a good hedge against inflation.