How to Stress Test a Multifamily Deal Before Your LOI: 5 Downside Scenarios When Agency Debt Sits Above 6.2%

Fannie Mae and Freddie Mac debt prices between 6.23% and 6.87% in September 2026, and the national multifamily vacancy rate hit a record 7.3% in December 2025. In this market, one base-case pro forma tells you almost nothing about whether a multifamily deal survives. This guide shows you how to stress test a multifamily deal before you submit an LOI: five downside scenarios, the break-even math behind each one, and a rule for setting your walk-away price.

Why One Base Case Misleads You in 2026

Every broker pro forma assumes the base case happens. Your job is to find the point where the deal stops working, then decide whether the distance between the base case and the break-even point protects your equity.

The 2026 market gives you three reasons to take this seriously. The CBRE H1 2026 Cap Rate Survey found the 10-year Treasury peaked at 4.67% in mid-May, and while roughly 60% of respondents expect no change in cap rates, more of the rest expect a rise, with infill multifamily the most bearish subtype. CBRE also expects effective asking rent growth to stay low for much of 2026. And insurance costs rose 55% per unit between 2021 and 2024, according to the National Apartment Association.

To keep the scenarios concrete, every example below uses one deal. Closing costs are left out for simplicity.

The base case produces a 1.38x DSCR, 5.3% year-1 cash-on-cash, a 12.5% levered IRR, and a 1.72x equity multiple. It looks fine. The five scenarios below show where it breaks.

Scenario 1: What a 100 bps Rate Move Does Before You Lock

Your rate is not fixed until you lock it, and the 10-year Treasury moved enough in 2026 to matter. Test a 100 bps increase first, because it changes both your cash flow and your loan size.

Mortgage Constant = Annual Debt Service / Loan Amount
Max Loan = NOI / (Required DSCR x Mortgage Constant)

Constant at 6.40%, 30-year amortization = 0.0751
Constant at 7.40%, 30-year amortization = 0.0831
Max Loan at 7.40% = $1,080,000 / (1.25 x 0.0831) = $10.40 million

At 7.40%, debt service rises to $864,090 and DSCR falls from 1.38x to 1.25x, right on a typical agency floor. The max loan at 1.25x now equals your $10.4 million loan almost to the dollar. Any move beyond 100 bps and the lender cuts proceeds, which forces you to bring more equity or renegotiate price. Levered IRR drops from 12.5% to 10.9%, and year-1 cash-on-cash falls from 5.3% to 3.9%.

A 7.40% rate also sits above your 6.75% going-in cap rate, so the deal flips to negative leverage. Our guide on underwriting a deal with negative leverage covers what to demand from the business plan when this happens. If the deal only pencils with bridge debt, run this scenario at bridge pricing too. Debt fund bridge loans price between 9.95% and 10.5% as of September 2026, according to Apartment Loan Store, and a floating-rate loan carries rate risk for the full term, not only until closing.

Scenario 2: How Much Vacancy Your Deal Absorbs

In a February 2026 National Association of Home Builders release, Cotality economist Molly Boesel put the national multifamily vacancy rate at a record high 7.3% in December 2025. The same release notes high supply pushed multifamily rents down 1% year over year. Your base case uses 7% economic vacancy. Stress it to 10%.

At 10% vacancy, year-1 NOI falls to $1,015,200, DSCR drops to 1.30x, and levered IRR falls to 8.7%. The loan stays safe, but the return slips below the IRR hurdle most LPs expect. Next, find the break-even point directly.

Break-Even Occupancy = (Operating Expenses + Debt Service) / Gross Potential Rent
                     = ($928,800 + $780,631) / $2,160,000
                     = 79.1%

Max Vacancy at 1.25x DSCR = 1 - (Operating Expenses + 1.25 x Debt Service) / GPR
                          = 1 - ($928,800 + $975,789) / $2,160,000
                          = 11.8%

This deal covers debt service down to 79.1% economic occupancy, and it holds a 1.25x DSCR up to 11.8% vacancy. A 4.8-point cushion above your 7% base case is reasonable. A cushion under 3 points leaves no room for one weak leasing season. For the full lender view, see our guide to how lenders size loans off DSCR and debt yield.

Scenario 3: An Expense Spike Led by Insurance

Pro formas often grow expenses at the same rate as rents. This scenario tests what happens when the two diverge. The National Apartment Association reports same-store insurance costs rose from $502 per unit in 2021 to $777 in 2024, including a 25% jump in 2023 alone. A Federal Reserve analysis of Trepp loan-level data puts median insurance costs at 4.78% of apartment revenue in 2024, up from 1.95% in 2000.

Stress year-1 operating expenses up 10%, about $774 per unit, and grow expenses at 5% per year instead of 3%. Rents still grow at 3%.

Year-1 DSCR holds at 1.26x, so the lender stays comfortable. Your returns do not. Levered IRR falls from 12.5% to 0.5%, and the equity multiple drops to 1.02x. You get your money back and almost nothing else.

The reason is compounding. When expenses grow 2 points faster than income on a 46% expense ratio, NOI shrinks every year, and exit value shrinks with it. Year-6 NOI, the figure a buyer capitalizes at your exit, falls from $1,252,016 in the base case to $1,024,798. At the same 7.00% exit cap, the sale price drops by more than $3.2 million. Check the T-12 against current multifamily expense benchmarks before you accept the broker growth rate.

Scenarios 4 and 5: Exit Cap Expansion and Slower Rent Growth

Your exit cap and your rent growth assumption drive most of your IRR, and neither sits in your control. Test them separately so you see which one your deal depends on.

Exit cap expansion

Your base case already assumes a 7.00% exit, 25 bps above the 6.75% going-in cap. Push it further.

• Exit at 7.50% (+50 bps): sale price drops to $16.69 million, levered IRR falls to 9.5%.
• Exit at 8.00% (+100 bps): sale price drops to $15.65 million, levered IRR falls to 6.5%.
• Break-even exit caps: IRR hits 10% at about a 7.4% exit, 8% at about 7.7%, and 0% at about 9.1%.

The 0% break-even at a 9.1% exit gives this deal a wide margin against losing equity. The 10% break-even at 7.4% gives it a narrow margin against missing your target return.

Slower rent growth

Cut rent growth from 3% to 1% while expenses keep growing at 3%. Year-1 numbers stay identical, so a first-year DSCR test misses this risk entirely. By year 5, DSCR slips to 1.34x and levered IRR collapses to 2.2%.

This scenario matches the CBRE outlook for low effective asking rent growth through much of 2026, with Austin and Denver projected to post negative asking rent growth. If your market sits in a supply-heavy metro, treat 1% rent growth as a realistic case, not a downside case.

How to Read the Results and Set Your Walk-Away Price

Put every scenario in one table. Add a combined downturn: 9% vacancy, year-1 expenses up 5% and growing 4% per year, 1.5% rent growth, and a 7.50% exit cap.

The table tells you three things about this deal.

1. Debt risk stays manageable. No scenario, including the combined downturn, pushes DSCR below 1.21x.
2. Equity risk sits in the growth spread. The two worst single scenarios both come from expenses outgrowing income, not from rates or cap rates.
3. The combined downturn wipes out 40% of your equity. Moderate versions of every risk at once return a 0.60x multiple, even though the loan never defaults.

Now set a walk-away price with two tests. First, the deal must clear your minimum IRR, say 8%, in the single scenario you consider most likely. Second, the deal must return 100% of your equity in the combined downturn. Lower the price and rerun each failing scenario until both pass, holding LTV at 65%.

Expense spike clears 8% IRR at:        $14.38 million
Combined downturn returns 1.00x at:    $14.18 million
Walk-Away Price = lower of the two  =  about $14.2 million
Implied going-in cap = $1,080,000 / $14,180,000 = 7.6%

Your walk-away price sits about 11% below the $16 million ask. Any price between $14.2 million and the $16 million ask is a negotiation. Paying the full ask means you are paying for the base case and absorbing every downside yourself.

How MultiVest Engine Runs These Stress Tests

Running eight scenarios by hand in a spreadsheet means eight copies of the model and eight chances for a broken formula. MultiVest Engine's Scenario Builder lets you apply a stress test to any financing scenario. Pick from five preset templates, Recession, Rising Interest Rates, High Vacancy, Expense Spike, and Market Downturn, or set custom adjustments to income growth, expense growth, interest rate, and exit cap rate. Apply the test to a duplicate of the scenario, and your base case stays intact for a side-by-side comparison.

Every conventional scenario runs through the same Full Analysis engine, which returns NOI, levered IRR, cash-on-cash, equity multiple, LP and GP waterfall splits, and the lowest-year DSCR across the hold, not only year 1. The lowest-year figure catches the slow-rent-growth risk a first-year test misses. You also stress the financing side by comparing Conventional, Bridge-to-Perm, and Creative Financing structures under the same downside assumptions.

Start every stress test from a clean NOI. Upload the broker T-12 and rent roll, let document ingestion categorize every line, and run the T-12 Normalizer before you stress anything. See the full workflow on the features page, review a sample underwriting report, or compare plans on the pricing page.

The Bottom Line

Run five scenarios before every LOI: a 100 bps rate move, 10% vacancy, a 10% expense spike with 5% annual expense growth, a 50 to 100 bps wider exit cap, and 1% rent growth. Calculate your break-even occupancy and break-even exit cap, then lower your price until the deal clears your IRR hurdle in the likely case and returns your equity in the combined downturn. In this example, the worst outcomes came from expenses outgrowing rents, not from debt terms, so test your growth spread hardest.

References

1. CBRE: U.S. Cap Rate Survey H1 2026
2. CBRE: U.S. Real Estate Market Outlook 2026, Multifamily
3. National Apartment Association: Premium Pulse, National Multifamily Insurance Cost Acceleration
4. Federal Reserve FEDS Notes: Rising Property Insurance Costs and Pass-Through to Rents for Apartment Buildings
5. NAHB: Multifamily Market Expected to Cool in 2026 as Vacancies Rise
6. Apartment Loan Store: Multifamily Apartment Loan Interest Rates