The 5 Assumptions That Quietly Break Multifamily Deals

Multifamily investing in Canada has entered a more disciplined phase. Capital is no longer abundant, debt is no longer predictably cheap, and rent growth is no longer universally accelerating. Yet many acquisition models still reflect habits formed in a very different environment. Deals rarely fail because of one dramatic miscalculation. More often, they unravel because of a handful of small, seemingly reasonable assumptions that compound over time. Individually, they appear harmless. Together, they erode margins, strain coverage ratios, and limit exit flexibility. In today’s market, understanding which assumptions carry hidden fragility is more important than finding the next growth story. What follows are five underwriting assumptions that deserve closer scrutiny, not because they are always wrong, but because they are often accepted without sufficient pressure testing.

Rent Growth That Outruns Local Income

Rent growth is the most common lever used to justify acquisitions, particularly in markets where going-in cap rates feel tight relative to financing costs. A 3% to 5% annual increase in rents can quickly transform a marginal deal into an attractive one on paper. The question is not whether rents can grow, but whether they can grow sustainably within the context of local wage trends and affordability constraints. In many Canadian markets, rent growth over the past several years was driven by supply shortages, rapid in-migration, and elevated replacement costs. Those forces were real, but they were also cyclical. If underwriting assumes continued rent growth that materially exceeds wage growth in the submarket, the model implicitly assumes tenants will absorb a growing share of their income toward housing. That may be possible for a period of time, but it rarely persists indefinitely. Affordability ceilings are real, particularly in markets without strong income expansion. Disciplined underwriting begins by anchoring rent assumptions to local economic fundamentals rather than recent trailing performance. Stress testing flat rent for a year or two, or moderating growth below recent averages, often reveals how much of a deal’s projected return depends on optimistic rent trajectories. If modestly lower growth materially compresses returns, the margin of safety may already be thin.

Vacancy and Expense Assumptions Based on Ideal Conditions

Stabilized vacancy in pro formas frequently reflects best-case performance rather than normalized performance. A property operating at 1% or 2% vacancy during a supply-constrained period may not sustain that level indefinitely. Even well-located assets experience turnover, renovation downtime, and leasing friction. Underwriting to a structurally tight vacancy assumption leaves little room for operational variability. A similar dynamic exists on the expense side. Insurance premiums, utilities, payroll, and capital reserves have all experienced volatility in recent years. Yet many models continue to apply historical expense ratios without fully adjusting for current cost realities. Underestimating operating expenses by even a small percentage can materially impact net operating income, particularly when combined with higher financing costs. More conservative underwriting incorporates normalized vacancy rates and forward-looking expense growth. It also allocates realistic capital reserves for building systems and lifecycle replacements. In an environment where debt service coverage is more closely scrutinized, precision in these inputs is not optional. It is foundational.

Exit Cap Rates That Assume Stability, and Debt That Assumes Improvement

Exit assumptions remain one of the most consequential variables in any multifamily model. Even underwriting to a “flat” cap rate relative to entry can be an embedded bet, especially if the acquisition cap rate itself reflects strong market sentiment. A modest expansion of 50 to 100 basis points at exit can materially compress equity returns. When projected performance depends heavily on stable or improving cap rates, the investor is exposed to forces largely outside operational control.The same principle applies to refinancing assumptions. Many deals implicitly rely on improved credit conditions at maturity, lower interest rates, tighter spreads, or more generous loan-to-value ratios. While those outcomes are possible, they are not guaranteed. Underwriting that depends on refinancing at more favourable terms to achieve target returns introduces an additional layer of uncertainty.

A more resilient approach assumes conservative exit pricing and debt terms that resemble current market conditions rather than anticipated improvements. If a deal remains attractive under those constraints, it is less dependent on macro tailwinds and more grounded in asset-level performance. This distinction becomes critical during periods of capital market recalibration. Multifamily investing has always rewarded disciplined operators, but the current environment is less forgiving of optimism embedded in spreadsheets. Rent growth may moderate. Vacancy may normalize. Expenses may rise faster than expected. Cap rates may adjust. Debt markets may not cooperate on schedule. None of these outcomes are catastrophic in isolation. They become problematic when layered onto a model that left no room for them.

The objective of underwriting is not to predict the most favourable outcome. It is to understand how a deal performs across a range of plausible conditions. Investors who scrutinize rent assumptions, normalize vacancy, account for expense volatility, and treat exit and refinancing scenarios with caution are not being pessimistic. They are preserving optionality. In Canadian multifamily today, returns are increasingly earned through discipline rather than momentum. The deals that endure will be those that work without perfect assumptions. Everything else is simply hoping the market cooperates.