Understanding the
Numbers.
This guide explains the key numbers investors use to evaluate a rental property: gross income, operating expenses, net operating income, cap rate, cash flow, cash-on-cash return, internal rate of return, and the APOD. Each term includes a clearly labeled illustrative example so you can see how the math works on any property you are evaluating.
About the examples: The numbers in the example boxes are hypothetical and were chosen only to show how each formula works. They are not a specific property, not Lehigh Valley market data, and not a prediction or promise of returns. Always verify figures against real property records and current local data before you invest.
Gross Income
Gross income is the total rent a property would produce at full occupancy, before any expenses. When sellers quote rental income, this is usually the number they lead with, so it pays to understand it.
The realistic version is called effective gross income: gross income minus an allowance for vacancy and collection loss, because no building is full and collecting every month. Work from effective gross income, not the theoretical maximum.
Say a hypothetical four-unit building rents each unit at $800 per month. Gross annual rent would be 4 × $800 × 12 = $38,400. With a $1,920 vacancy and collection allowance, effective gross income would be about $36,480. Made-up numbers to show the math, not a real property.
Operating Expenses
Operating expenses are the recurring costs of running a property: property taxes, insurance, property management, maintenance and repairs, utilities the landlord pays, and reserves for vacancy and big-ticket items like roofs and systems. Debt service (the mortgage payment) is not an operating expense, and neither is the purchase of capital improvements.
Real expense numbers come from the current tax bills, insurance premiums, and operating statements, not from a seller's estimate. If an expense is missing from the packet, ask for it.
Net Operating Income (NOI)
Net operating income is the property's operating profit: effective gross income minus operating expenses, before debt service and income taxes. NOI is the number that cap rate is built on, and it is what lenders underwrite against, so getting it right matters.
$36,480 − $16,480 = $20,000 in NOI for the hypothetical building above.
Cap Rate
The capitalization rate (cap rate) is net operating income divided by the property value or purchase price. It expresses the building's operating return as a percentage, before financing, which makes it useful for comparing one property to another on an apples-to-apples basis.
There is no universal "good" cap rate. What is normal varies by property type, condition, location, and the current market, and a higher cap rate often comes with higher risk or deferred maintenance. Use cap rate to screen and compare, never as a standalone verdict.
With $20,000 in NOI on a hypothetical $250,000 purchase price, the cap rate would be $20,000 ÷ $250,000 = 8%. This is arithmetic on made-up numbers, not a market claim or a target.
Full walkthrough: Understanding Cap Rates.
Cash Flow
Cash flow is what is left after the mortgage is paid: NOI minus annual debt service. Positive cash flow means the rent covers the operating costs and the loan with money to spare; negative cash flow means the owner is writing a check every month. Most investors want positive, stable cash flow from day one.
If the hypothetical building's mortgage costs $15,000 per year, cash flow would be $20,000 − $15,000 = $5,000 per year, or about $417 per month. Example numbers only.
Cash-on-Cash Return
Cash-on-cash return measures the annual pre-tax cash flow against the cash you actually put in: the down payment, closing costs, and any initial repairs or improvements. Because it is based on your invested cash, it reflects the leverage in the deal, which is exactly why it differs from cap rate.
If the hypothetical buyer invested $62,500 (down payment, closing costs, and initial work), cash-on-cash would be $5,000 ÷ $62,500 = 8%. The percentage changes whenever leverage or cash invested changes, so it is personal to each buyer's deal.
Full walkthrough: Cash-on-Cash Return.
Internal Rate of Return (IRR)
The internal rate of return is the projected annualized rate of return over the whole holding period, and it is the most complete performance measure in the toolkit because it accounts for the timing of every cash flow plus the eventual sale. In plain terms, it is the discount rate at which the present value of all future cash flows equals your initial investment.
IRR is a projection, not a guarantee. It depends on assumptions: future rent, expense growth, the holding period, the sale price, and sale costs. Change one assumption and the IRR moves, sometimes sharply. A great-looking IRR built on optimistic assumptions is still just an assumption.
In a spreadsheet or financial calculator, you lay out the cash flows year by year: the cash you invest in year zero (a negative number), the annual cash flow in each year, and the assumed net sale proceeds in the final year. The IRR function solves for the rate that makes the present value of those flows equal the initial investment. The result is often stated as an annual percentage.
Full walkthrough: Internal Rate of Return.
Rate of Return
Rate of return is the general term for the percentage an investment produces relative to the money put in. It can be calculated many ways: over a year, over the holding period, on cash flow only, or including the sale. That flexibility is exactly why investors prefer precise metrics like cash-on-cash return and IRR.
When someone quotes a "rate of return" without saying how it was calculated, ask how. The same property can show a very different rate depending on whether appreciation, leverage, and timing are included.
The APOD and a Full Investor Packet
The APOD, or Annual Property Operating Data, is a one-page form summarizing a property's annual income, expenses, and net operating income. It is usually the first page of a deal package, giving buyers and lenders a quick financial snapshot of the building.
A complete investor packet typically includes much more than the APOD:
- The APOD itself
- A current rent roll, unit by unit
- Two to three years of operating statements where available
- Current tax and insurance bills
- Lease summaries, including terms, deposits, and expirations
- Capital expenditure history and plans
- Photos, condition notes, and any inspection reports
Treat the packet as a starting point, not the truth. Verify the rent roll against actual leases, check expenses against tax records, and confirm vacancy history. Tim reviews the full packet with buyers on every property he represents, and the numbers have to reconcile before a deal makes sense.
Putting It All Together
No single number decides a deal. Cap rate tells you about the building, cash-on-cash tells you about your cash, and IRR tells you about the full picture over time. The discipline is to run them all from verified inputs, then compare the property against other opportunities in the same market.
The step-by-step workflow lives in the Investment Property Worksheet, and income and expense detail is in Gross vs Net Income. Both use the same formulas shown here.
Frequently Asked Questions
What is the difference between cap rate and cash-on-cash return?
Cap rate divides net operating income by the property value and ignores financing, so it compares buildings on an even footing. Cash-on-cash divides your actual cash flow by the cash you invested, so it reflects your leverage and your personal deal structure. One tells you about the property; the other tells you about your investment in it.
Is a higher cap rate always better?
No. A high cap rate can signal a stronger return, but it can also signal higher risk, deferred maintenance, weaker rent growth, or a difficult location. Low cap rates can mean a safer, more liquid asset. Compare cap rates among similar properties in the same market, and look behind the number at the condition and the quality of the income.
What is a realistic cap rate in the Lehigh Valley?
There is no single honest answer, because cap rates vary by property type, condition, and neighborhood, and they move with the market. What matters is comparing a candidate property against recent sales of similar properties in the same area. Tim runs that comparison with current local data for every deal he evaluates.
What should I do if the seller's income numbers look too good?
Ask for proof: tax returns, actual operating statements, and the real rent roll with signed leases. Compare effective rent against what similar units in the area actually rent for. A packet that cannot be verified is a red flag, not a number to trust.
Is IRR a guarantee of what I will earn?
No. IRR is a projection built on assumptions about rent growth, expenses, the holding period, and the sale price. It is a powerful way to compare scenarios, but the real result depends on what actually happens. Ask what assumptions the projection uses, and test how the number changes when the assumptions change.
The numbers are where every good investment decision starts, and getting them right requires current, local data. Tim Tepes runs the full analysis with buyers across Northampton, Lehigh, and Carbon Counties, and he is glad to walk through the math on a property you are considering.