I have the understanding that no one expects residential real estate rental to be cash-flow positive with a full mortgage. It's extremely rare and basically a complete no-brainer if you can find a property that is cash-flow positive with a mortgage. Generally, one looks at equity and tries for net-worth positive. Which is simple to say, but is made more complex by older mortgages giving more equity for an equal payment.
Of course, with an interest-only mortgage, yes one would need to be cash-flow positive, because there is no such thing as gaining equity. Again, my understanding is that such properties are extremely rare.
