A rental property pro forma can look incredibly precise.

But every one of those numbers starts with an assumption. And when those assumptions are projected 10, 20, or even 30 years into the future, small differences can meaningfully change the outcome on the page.

On last week’s Not Your Average Investor Show, I wanted to make one part of that process easier by showing you where you can check some of those assumptions yourself using free market data.

Because before I build expectations around a projected return, I want to understand where the numbers came from and whether the history gives me a reasonable basis for using them.

Let’s dive in.

Start With the Assumptions Behind the Return

A rental property pro forma can look remarkably precise, but the projections are only as useful as the data and assumptions behind them. Before deciding whether a deal looks attractive, there are four numbers I pay particularly close attention to:

• Purchase Price: The price you are actually paying to acquire the property.
• Home Price Appreciation: How much home values in that market have historically grown over time.
• Current Rent: What a single-family rental in that market is generating today.
• Rent Growth: How much rents have historically increased over time.

Each one can change what the investment is projected to look like years from now.

Home price appreciation deserves particular attention because we talked about how it can represent 60 percent to 80 percent of a rental property’s return over a full market cycle.

That is a big piece of the picture to leave unquestioned.

So before deciding whether the projected return looks attractive, I think it helps to first understand which assumptions are driving it.

Three Free Ways to Check the Numbers

The good news is that investors do not need expensive research subscriptions to start checking these numbers.

👉 3 Free Tools to Check Rental Property Market Data

1. Redfin for the current purchase price environment

Redfin’s housing market data lets you look at median sale prices, homes sold, inventory, and other market information across metro areas.

In the August data we reviewed, Jacksonville’s median home sale price came in around $372,000.

The exact number can vary slightly depending on the source. What I am looking for is whether the data is telling a similar story.

2. FHFA for long-term home price appreciation

This is the one I would spend the most time understanding.

The Federal Housing Finance Agency gives us a much longer view of home price history.

For Jacksonville, we looked from Q2 of 1991 through Q2 of 2026. That gave us about 35 years of data, while comparing the same quarter to reduce the effect of normal seasonal changes.

That history worked out to roughly 4.8 percent annual home price appreciation for Jacksonville.

Instead of relying on what happened during one unusually strong period, we can see how the market performed across several different market environments.

3. Zillow for current rents and rent growth

Zillow Research is useful because it lets us look specifically at single-family rents rather than combining them with multifamily properties.

For Jacksonville, the data showed rents increasing from about $1,185 in 2015 to about $2,075 in 2026.

That works out to ~5.2% annual rent growth over that period.  However, I’d discount that number by 25% simply because rents from 2015-2026 have grown at a faster rate than normal.  Unfortunately, great data on rents that is free and also spans multiple markets and the US just hasn’t existed for very long.  

That math gets us to a ~4% annual rent growth figure for Jacksonville (which I validated against our consultant’s data that we pay a pretty penny for.) 

At this point, we have found the numbers.

But that still leaves an important question: What do those numbers actually mean?

A Number Becomes More Useful With a Benchmark

Finding a number is only the first step. We still need context to understand whether that number is strong, weak, or reasonable.

Take Jacksonville’s 4.8 percent historical home price appreciation rate.

By itself, 4.8 percent does not tell me very much.

👉 Is Your Market’s Home Price Growth Above Average?

But when we ran the same type of analysis for the United States, the historical rate came out to roughly 4.3 percent. 

Now I have something meaningful to compare it with.

That same principle can apply when looking at another market, rent growth, or purchase prices. I want to compare similar data over similar periods so I understand what the number actually represents.

It is also why I am cautious about using an unusually strong five- or ten-year stretch to project the next decade.

The historical number may be accurate. But if the period itself was unusual, carrying that same rate forward can make the future projection look stronger than the longer history supports.

That gives us a simple process I think is worth remembering:

• Know the assumption: Identify which numbers are driving the projection.
• Find the data: Look at the history yourself.
• Compare with the right benchmark: Give the number enough context to understand what it means.

NOT YOUR AVERAGE INSIGHT: They Are Not All “Assumptions”

👉 The Pro Forma Assumptions Investors Should Fact-Check

When I think about all the numbers in a rental property pro forma, I come back to the Pac Man principle.

Home price appreciation can represent 60 percent to 80 percent of a rental property’s return over a full market cycle, so I think it deserves the most weight when choosing a market.

Then there are the numbers that depend much more on the operator, especially cash flow.

Those numbers usually come from one of three places:

1. Looked up: Public data or standard assumptions
2. Bought: Research purchased from outside consultants
3. Proprietary: The operator’s own historical performance

That last category is important because an experienced operator does not have to guess at every number. If they have managed enough properties over enough time, they can build assumptions around what they have actually experienced with rents, occupancy, maintenance, turns, and operating costs.

So the combination I am looking for is a market with long-term growth that exceeds the national average, prices that can still support positive cash flow, and an operator with enough history to build its pro forma from its own performance data.

That is also the standard we have built around in Jacksonville. The market has historically appreciated above the national average, while still supporting positive cash flow, and the operating assumptions in our pro formas come from our own historical performance.

So the bigger lesson is not just knowing where to find the numbers. It is understanding which numbers are created by the market, which are influenced by the operator, and how much real history sits behind each assumption.

Just remember… Don’t Be Average.
Gregg Cohen
Co-Founder, JWB Real Estate Capital