Sensitivity Analysis for Investment Decisions

One-way sensitivity analysis varies a single input while holding all others constant. For a typical multifamily acquisition, construct a table showing how the levered IRR changes as rent growth varies from 0% to 6% in 1% increments. If the base-case IRR is 14% at 3% rent growth, the table might show: 0% growth → 8.2% IRR, 1% → 10.1%, 2% → 12.0%, 3% → 14.0%, 4% → 16.1%, 5% → 18.3%, 6% → 20.6%.

This reveals that each percentage point of rent growth adds approximately 2% to the IRR — a steep sensitivity. Now run the same analysis for the exit cap rate. If the base case assumes a 6.0% exit cap: 5.0% exit → 19.8% IRR, 5.5% → 16.8%, 6.0% → 14.0%, 6.5% → 11.4%, 7.0% → 9.0%, 7.5% → 6.7%. Each 50-basis-point increase in exit cap reduces IRR by approximately 2.5 percentage points — even steeper sensitivity. This tells the investor that exit cap rate is the single most important assumption.

A tornado diagram visualizes the relative importance of each variable by showing the IRR range produced when each variable moves between its low and high cases, holding all others at base values. Variables are stacked from widest range (most impactful) at the top to narrowest (least impactful) at the bottom, creating a tornado shape.

For a typical leveraged real estate investment, the tornado typically ranks as follows: (1) Exit cap rate — widest bar, because it affects the terminal value which is often 60–70% of total present value. (2) Rent growth — directly drives NOI trajectory and terminal value. (3) Interest rate on debt — determines debt service cost and cash-on-cash returns. (4) Vacancy rate — reduces effective gross income. (5) Operating expense growth — erodes NOI margin. (6) Renovation cost overrun — affects initial capital outlay for value-add deals. This ranking tells the investor where to focus due diligence effort and negotiate hardest.

Scenario analysis examines the combined effect of multiple variables changing simultaneously — bridging the gap between one-at-a-time sensitivity analysis and full Monte Carlo simulation. The three standard scenarios are: Base case (most likely assumptions), Optimistic (favorable market conditions), and Pessimistic (adverse conditions). A well-constructed pessimistic scenario for a 2024 multifamily acquisition might assume: rent growth of 1% (vs. 3% base), exit cap rate of 7.5% (vs. 6.0%), vacancy of 8% (vs. 5%), and interest rate increase of 100 bps at refinancing.

The pessimistic scenario might produce a levered IRR of 2–4% versus the base case of 14%, but still positive — meaning the investment survives adverse conditions without a total loss. A break-even analysis identifies the point at which the investment returns exactly the cost of capital: if the break-even exit cap rate is 8.2%, the investor assesses whether cap rates have ever exceeded 8.2% in this market. According to Real Capital Analytics, national multifamily cap rates peaked at approximately 7.5% during the GFC — suggesting the break-even provides a reasonable margin of safety.