Every deal you look at arrives with two sets of numbers. One is the pro forma, a tidy projection of what the property could earn, almost always written by the person selling it. The other is the actuals, the dull record of what the building really collected and really spent over the last twelve months. They rarely agree, and the gap between them is where most first-time buyers overpay.
The pro forma is not lying to you. It is doing its job. The seller and the listing agent are paid to show the building at its best, with the vacancy assumed away, the management assumed free, and the rents marked to a number the units have never actually charged. Your job is the opposite: take the projection apart, rebuild it from the receipts, and then hold it to one consistent standard so the deal you buy is the deal you can sell later.
What each number really is
A pro forma is a forward projection. It states assumptions (target rents, an occupancy rate, an expense load) and arithmetic flows from there. It is the right tool for asking “what could this be,” and the wrong tool for asking “what is this today.” You can read the term itself in the pro forma glossary entry.
Actuals are the historical record: the income/expense statements, the bank deposits, the property tax bills, the insurance binder, and the rent roll showing who pays what and who is behind. The most useful form is the T12, the trailing twelve months laid out month by month, because a slow leasing summer or a one-time roof repair disappears into an annual total but jumps out of a monthly grid. Ask for the T12, the current rent roll, and the actual tax and insurance bills. If a seller will only hand you a pro forma, you have learned something already.
The normalization standard
Here is the standard I underwrite every deal on, and the one I built into my own books because eyeballing it never held up. Two line items get charged on every property regardless of what is happening today: vacancy and management. Charge them even when the building is full. Charge them even when you plan to manage it yourself.
- Always underwrite 5% vacancy, even at full occupancy. A building that is 100% leased the day you tour it will still turn a unit over, sit empty between tenants, and lose a few days to make-ready. Five percent is a defensible floor for a stable small property; soft markets and student rentals run higher. The mechanics of physical versus economic vacancy are in the vacancy rate guide.
- Always charge 8% management, even if you self-manage. Your time is not free, and the moment you want to sell, refinance, or step back, someone has to be paid to do the work you are doing now. If the deal only pencils because your labor is uncosted, it is a job you bought, not an asset. The 8% to 10% fee math is broken down in property manager vs self-managing.
- Mark every other expense to the actual bills. Taxes reassess on sale in many counties, so use the projected reassessed figure, not the seller's frozen rate. Insurance gets quoted for you, not inherited. Repairs and the reserve line come from the T12 and a per-door reserve, not from an optimistic round number.
The side-by-side, worked out
Say you are looking at a fourplex listed at $520,000. The seller's pro forma shows market rent of $1,500 per unit, no vacancy, and a thin expense load. The T12 shows three units actually rented at $1,350 and one at $1,400, with real costs you can read off the bills. Run all three columns and the spread is the whole story.
Seller pro forma (gross potential):
- Gross rent: 4 units × $1,500 × 12 = $72,000
- Vacancy: $0 (assumed full)
- Management: $0 (assumed self-managed)
- Other operating expenses: $18,000
- Net operating income: $72,000 − $18,000 = $54,000
- Cap rate at $520,000: 10.4%
Raw actuals (T12, as collected):
- Gross rent: ($1,350 × 3 + $1,400) × 12 = $65,400
- Vacancy: already reflected in what was collected
- Management: $0 (prior owner self-managed)
- Other operating expenses (actual bills): $22,400
- Net operating income: $65,400 − $22,400 = $43,000
- Cap rate at $520,000: 8.3%
Normalized (the number I would offer on):
- Effective gross income: $65,400 × (1 − 0.05) = $62,130
- Management at 8% of EGI: $62,130 × 0.08 = $4,970
- Other operating expenses (actual bills): $22,400
- Net operating income: $62,130 − $4,970 − $22,400 = $34,760
- Cap rate at $520,000: 6.7%
Same building, three numbers: a $54,000 NOI in the listing, a $43,000 NOI on the receipts, and a $34,760 NOI once you cost the vacancy and your own time. The pro forma cap rate of 10.4% is the one printed in the ad. The 6.7% is the one you actually live with. Buy on the third column and the first column becomes upside you might earn, not value you paid for. For the full deal walk-through end to end, see how to analyze a rental property deal.
Where seller pro formas drift from the receipts
None of this means a seller is cheating you. It means the seller and you have different incentives, and the assumptions tilt toward the sale. These are the lines to check first, every time.
- Market rent that no unit charges. A pro forma rent of $1,500 against actual leases at $1,350 is a $150 monthly bet you have to win four times over. Verify it against real listings, not the listing agent's word; the method is in how to find rent comps.
- Vacancy set to zero. The most common single edit. A snapshot of full occupancy is not an annual vacancy rate.
- Management left off entirely. If the seller self-managed, the line reads $0, which quietly transfers their unpaid labor onto your return.
- Property taxes at the seller's old assessment. A sale often triggers a reassessment near the purchase price, which can move the tax line by thousands.
- No reserve and no repairs. A pro forma with a clean expense load and no capital reserve is describing a building that never ages. The line-item view of where money actually goes is in the operating expense ratio guide.
Turning the rebuilt numbers into a decision
Once you have a normalized NOI you trust, run it through the metrics that actually drive a buy-or-pass call. Cap rate tells you the unlevered yield; cash-on-cash tells you what your invested dollars return after the loan. Keep the two distinct, because a deal can look fine on cap rate and thin on cash flow once debt is in. The difference is laid out in NOI vs cash flow, and you can run your own figures in the cap rate calculator and the cash-on-cash calculator.
This habit pays off long after closing. The normalized number you bought on becomes the baseline you track against, month after month, so you know early when reality is drifting from the plan. Building and protecting that baseline across a few doors is the subject of the rental property portfolio guide.
Holding the standard after you own it
The discipline does not end at the closing table. The same two normalizations that protect your offer also keep your reporting honest once you own the place, which is why I wired them into the tool I built. rents.ai computes its headline cap rate, NOI, and cash-on-cash on a normalized annual pro forma (a 5% vacancy factor and an 8% management rate) and lets you set those numbers beside your raw actuals, so you can see both the way a buyer would underwrite and the way the building actually ran. It will not pull a market-rent feed for you, though: the rent you compare against is the figure you enter, so your comps research still has to be your own.
Two numbers describe every deal, and the cheaper one wins your money. Buy on the receipts, normalized to a standard you would accept from your own eventual buyer, and let the pro forma be the upside you earn rather than the price you pay.
The figures above are a hypothetical example to show the method, not an appraisal or a promise of return. Verify every line against the actual statements, leases, and bills for a specific property, and have your own numbers reviewed before you make an offer.