Multifamily Underwriting Fundamentals High Net Worth Investors Should Know

High net worth investors are typically highly intelligent and accomplished within their respective fields. Surgeons, dentists, corporate executives — they've spent decades becoming experts in complex disciplines.

From the outside, a multifamily real estate deal looks simple by comparison. Apartments rent for a monthly rate. Expenses are deducted. There are some loan payments. You sell after a couple of years. Nothing too complex, right?

The reality is that multifamily underwriting is filled with nuances — small levers that experienced developers and sponsors know how to pull to make a deal look more attractive than it actually is. These aren't always outright misrepresentations. In many cases, they live in gray areas that are technically defensible, but economically misleading.

And if you're not looking for them, you won't see them.

Below are a few of the most common underwriting nuances that we've come across that can materially distort how a deal actually performs.

Other Income

Base rent is relatively straightforward to diligence. You can go on Apartments.com, pull comparable properties, and quickly get a sense for what the market is charging for a one-bedroom or two-bedroom unit. It's not perfect, but it's directionally reliable.

Other income, on the other hand, is one area where deal sponsors can get "creative."

Multifamily operators often layer in additional fees — parking, pet rent, valet trash, admin fees, CAM charges — that can meaningfully increase the total cost to rent to the tenant. In isolation, each one may seem reasonable. In aggregate, they can become a hidden rent increase.

There are two common ways this gets manipulated:

• Charging for things competitors don't charge for. A property might introduce new fees that simply don't exist at competing properties. This effectively inflates renters' cost to own without showing up in the base rent comparison.
• Matching pricing without matching quality. A comparable property might charge $100/month for covered garage parking. The subject property also charges $100/month for parking. If that's all the digging you do, it might seem reasonable. However, what if the subject property's parking is surface parking? In that scenario would it be reasonable to also charge the $100/month? What if the market rate for surface parking was $0 in that submarket?

The same dynamic plays out with CAM (Common Area Maintenance) fees. One property may justify a $100/month fee by offering high-quality amenities, fast internet, and well-maintained shared spaces. Another may charge the same amount while offering a far inferior experience.

What's really happening in many of these cases is a shift: base rent is being partially hidden in "other income." It allows a developer to show a base rent rate comparable to the market, which is what most investors pay attention to, when in actuality the financial projections rely on achieving above market rates.

You'll often hear the rebuttal: "Tenants don't pay attention to fees." That's not how renters behave in the real world. This is just wrong. A tenant considering a $1,500/month apartment is highly price sensitive. A $50–$100 difference in total monthly cost is meaningful. Renters absolutely calculate it — whether explicitly or intuitively — and make decisions accordingly.

The financial impact of getting this wrong is not trivial. If a 100-unit property is underwritten with $300/month/unit in other income but only achieves $200/month/unit, that's a $100/month/unit shortfall. On an annual basis, that's $120,000 of lost revenue.

Concessions and the "Sticker Price" Trap

Concessions — typically free rent for one or more months — are one of the most misunderstood aspects of multifamily underwriting.

Developers often assume they can use concessions as a temporary leasing tool. The logic goes like this: offer 1–2 months free rent to attract tenants, get them comfortable with the "headline" rent, then remove concessions at renewal and capture full rent.

Tenants don't think in terms of headline rent. They think in terms of effective rent — what they're actually paying over the course of the lease. If a unit is advertised at $1,800/month with two months free on a 12-month lease, the effective rent is closer to $1,500/month.

If competing properties are offering similar effective rents, removing concessions without adjusting the headline rent often results in one of two outcomes: occupancy drops, or concessions quietly return. In both cases, the original underwriting assumption — that concessions are temporary — proves overly optimistic.

When reviewing a deal, you should normalize to effective rent. If the sponsor is underwriting a clean transition from concession-heavy leasing to full-market rents without disruption, that's a major assumption — and one that deserves scrutiny.

General Vacancy Allowance

In multifamily underwriting there is a concept called general vacancy allowance. This is a deduction to income that is forecasted to account for how many tenants vacate their units in a given year and how long it then takes to find a new tenant for that unit.

The more turnover and the longer it takes to find a new tenant, the higher the vacancy allowance should be.

In good submarkets with favorable supply/demand dynamics, a 5% allowance is fairly typical. This is meant to approximate it taking 30 days to re-lease a unit once it's vacant on about 50–60% of the units turning over each year. You'd typically underwrite the general vacancy allowance by looking at the average occupancy of comparable properties over the last year or so.

One thing we're seeing right now is, despite comparables suggesting vacancy allowance should be 6, 7, or 8%, and submarket dynamics suggesting the vacancy rates will stay elevated for several years, sponsors continue to underwrite 5% because that's been the standard from basically 2014–2022 in good submarkets.

Again, the difference between 5 and 7% may not seem like a big issue, but going back to the example of a 100-unit property with $1,500/unit/month rents, that change from 5 to 7% has a $720,000 impact on the stabilized value of the asset.

Operating Expenses: The Insurance Blind Spot

Insurance is another operating expense that has become increasingly difficult to underwrite accurately — and one that sponsors frequently get wrong.

Over the past several years, property insurance premiums have risen sharply across much of the country, particularly in states like Florida, Texas, and California where climate-related risk has caused carriers to exit markets or reprice dramatically. A sponsor benchmarking insurance costs against a property acquired in 2019 or 2020 will almost certainly be using a figure that no longer reflects the current market.

Beyond the sticker price, there are structural issues worth scrutinizing. Some sponsors underwrite low deductibles without accounting for the premium impact. Others rely on blanket policies across a portfolio that may not adequately cover a standalone asset. And in some cases, coverage limits are set at replacement cost figures that are years out of date — meaning that in the event of a significant loss, the insurance payout may not be sufficient to make investors whole.

Operating Expenses: The Property Tax Blind Spot

Operating expenses are another area where operators can hide aggressive underwriting assumptions and property taxes are often the biggest source of this over-optimism. Newer, higher-cost properties typically have a much higher assessed value than older comps. That translates directly into higher property taxes.

Additionally, many comparable properties — especially in states like California — benefit from laws that suppress property tax growth for owners. Under rules like Proposition 13, taxes may only increase ~2% per year, regardless of how much the underlying property value has appreciated.

If a sponsor is benchmarking expenses against these comps without adjusting for tax differences, the subject property's expenses may be understated. And unlike some other line items, property taxes aren't something you can "operate" your way out of. They're structural.

Texas presents the opposite problem. The state has no cap on commercial property tax growth, and as a non-disclosure state — where sale prices are not publicly recorded — appraisal districts value multifamily assets using the income approach, meaning the assessed value is driven by market rent and cap rate assumptions, not what the buyer actually paid. With some of the highest effective property tax rates in the country and annual reassessments, a sponsor who doesn't model this carefully is leaving one of the largest operating expense items largely to chance.

The Takeaway

High net worth investors are often intelligent, experienced businesspeople, but many lack the experience needed to audit these multifamily underwriting nuances. Sponsors know this and can use them to make projections look better than reality. This lack of expertise can lead to investor losses or materially lower than expected returns.

High net worth investors can protect themselves by becoming familiar with these details — or engaging experts, like AB CRE Advisors, to help them navigate the complex issues.