Per-unit vacancy math hides the real number
If one unit sits vacant for a month, you lose one month of rent. That's the simple version — and it's the wrong one for a portfolio. The real cost of vacancy at scale includes the rent you lose, the utilities you still pay, the make-ready between tenants, the leasing time, and the compounding effect of a higher portfolio vacancy rate on your reported returns.
The four cost layers most investors miss
Lost rent is the obvious layer. The three hidden layers are: (1) carrying costs — taxes, insurance, and minimum utilities that keep running during vacancy; (2) make-ready — cleaning, repairs, and turnover coordination that runs $800–$2,500 per unit per turn; and (3) leasing time — the 14–45 days it takes to find, screen, and place a qualified tenant. At portfolio scale, these layers compound.
A worked example across 20 doors
Take a 20-door portfolio at $1,400 average rent with a 10% vacancy rate. Lost rent is $33,600/year. Add carrying costs at roughly $150/unit/month during vacancy ($3,600/year), make-ready at $1,200/unit across the two expected turns ($2,400/year), and leasing time cost at half a month's rent per turn ($1,400/year). The real vacancy cost is closer to $41,000 — about 22% more than the headline number suggests.
Why portfolio-level reporting changes the decision
When each property reports separately, a 10% vacancy rate looks like a manageable per-unit problem. When you roll it up across 20 doors, the dollar exposure becomes large enough to justify a dedicated leasing pipeline and a portfolio manager whose compensation is tied to occupancy. That's the shift from accidental landlord to portfolio operator.
The takeaway
If you're managing a portfolio and only counting lost rent, you're undercounting your vacancy cost by roughly 20–25%. Run the full four-layer model on your own numbers — then compare it to what a professional manager with a 4% portfolio vacancy rate would save you.