A vacant month never sends you a bill. That is exactly why it is the most underestimated line in rental underwriting. One empty month out of twelve is about 8% of your gross rent gone, and it arrives with no due date, no invoice, and no entry in the "rent minus mortgage" math that talked you into the deal. It simply does not show up in the account.
And the lost rent is the small part. A turn — one tenant out, the next one in — drags make-ready costs, a leasing fee, utilities back in your name, and however many days the unit sits while you find someone. Priced honestly, one ordinary turn costs roughly three months of gross rent. Here is that number line by line, why units sit, and the schedule that closes the gap.
the true cost of one turn
Start with a unit renting at $1,400 a month. The tenant gives notice, moves out at the end of the month, and the unit sits about 45 days before the next lease starts. The numbers are round and illustrative, but the shape holds everywhere.
Rent lost over 45 empty days is about $2,100. Make-ready runs about $1,500 on a unit that was treated decently: paint, a deep clean, a flooring patch, new blinds, and the small repairs you deferred while someone was living there. A rough turn with pet damage or a dead appliance reaches $3,000 without trying. Then the leasing fee, typically half to a full month's rent whether a manager runs it or you spend the evenings yourself: call it $700. Then $200 for utilities, lawn care, and turn-on fees while every service is billed back to you.
That is $4,500 out of a single door. Against $16,800 of annual gross rent, one turn is about 3.2 months of rent — a quarter of the year. Measured against cash flow it is uglier: a well-bought single-family that nets $250 a month produces $3,000 a year, so one routine turn erases more than a year of profit. Vacancy is not a maintenance event you absorb; on most rentals it is the largest single expense of the year it lands in.
Which is why vacancy belongs beside every other recurring cost, not in a footnote. The breakdown of rental property operating expenses puts it next to maintenance, capex, management, taxes, and insurance — all subtracted before you look at the mortgage.
why units sit
Four things keep a unit empty longer than the market requires, and all four are yours.
Price. The market sets the rent; you only choose how long to argue with it. A unit listed $75 over the neighborhood usually rents at the neighborhood number anyway, weeks later — and those weeks cost more than the $75 could earn in a year. Read the first week of inquiries: steady calls means you are priced right, silence means every extra week costs more than the cut you are refusing to make.
Condition and photos. Renters shop the way buyers do, and they shop fast. Scuffed paint, a dated bathroom, and a neglected lawn are not dealbreakers alone, but together they move your unit to the bottom of a stack of ten. A $600 paint-and-clean that pulls two weeks off market time paid for itself the day it finished. And the photos are the entire first showing: ten bright, wide, straight shots beat three dark phone pictures every time, for one afternoon of work.
Response time. Rental leads go stale in hours, not days. The applicant who tours today signs today; the one who waits two days for a callback has already put a deposit somewhere else. If you cannot answer inquiries the same day, that alone is worth paying a manager for.
The tenant you approved. This one survives every fix above, because it was decided months earlier. Someone who cannot comfortably carry the rent, or who has broken the last two leases, hands you a turn on their own schedule and often a repair bill with it. Vacancy control starts at the application, which is why tenant screening is a vacancy tool first.
the retention math
Here is the calculation most landlords get backwards. Your tenant pays $1,400 and the market has drifted to $1,450. Push the renewal to market and you gain $50 a month, or $600 a year. If that push costs you the tenant, you spend $4,500 to collect it — about seven and a half years of the higher rent to pay back one turn, and only if the replacement stays that long.
So renewing modestly under market is usually the profitable move, and a small increase a good tenant accepts beats a large one they refuse. That is a default, not a law. It flips when the gap gets big: a unit sitting $300 under market gives up $3,600 a year, and the turn pays for itself in about fifteen months. It flips again when the tenant is the problem — chronic late payment, damage, or lease violations are worth a turn at almost any price.
Mechanically, retention is a calendar habit more than a negotiation. Ask about renewal roughly 90 days out, before the tenant starts browsing listings out of curiosity. Put a specific number and deadline in writing instead of opening a conversation. Fix the thing they have mentioned twice, because a $200 faucet buys goodwill far cheaper than $4,500 buys a stranger.
section 8 and vacancy
Housing choice voucher tenants move the vacancy profile in both directions, so understand the trade before assuming it is a win. Voucher tenants tend to stay considerably longer than market tenants: waitlists in strong markets run for years, so the voucher is valuable, and moving means re-qualifying and getting a new unit inspected. Fewer turns is where the real money is — a tenant who stays four years instead of two roughly halves your lifetime turn cost. The rent is steadier too, with a large share arriving from the housing authority on a schedule and the ceiling published rather than guessed.
The cost is a slower start. Between tenant approval, the inspection, any re-inspection you earn by failing on a missing smoke detector, and contract execution, the gap between an approved applicant and the first payment commonly runs 30 to 60 days — and you carry the mortgage through all of it. A second exposure comes later: if a unit fails a periodic re-inspection and you miss the repair deadline, payments can be suspended until you cure it, which behaves exactly like vacancy on a unit that is not even empty.
Net it out and the trade usually favors a buy-and-hold operator: a slower first fill, materially fewer turns across the hold. Just underwrite it correctly — budget one to two months of carrying cost into the acquisition instead of assuming rent starts the week you close.
the 90-day pre-lease playbook
Most vacancy is self-inflicted timing: the unit sits because marketing started the day the keys came back instead of six weeks earlier. The fix is a schedule you run on every lease, stay or go.
Two details make it work. Book the make-ready trades before the move-out date rather than after the walkthrough — a painter who can start Tuesday beats one who is $200 cheaper and free in three weeks. And screen applications as they arrive, so the next lease is signed while the current tenant is still packing. Done properly the gap is measured in days, and most of that $4,500 never happens.
underwriting vacancy honestly
Which brings it back to the spreadsheet. A sane vacancy assumption for a stabilized long-term rental is 5% to 8% of gross rent, and translating it into days helps you pick one. Five percent is about 18 empty days a year — one turn every two to three years, filled fast. Eight percent is closer to a month a year, which is what a high-turnover unit, a soft submarket, or a slow-responding owner actually produces. Pick the number that matches the property and your operation, not the one that rescues the deal.
Zero vacancy is not aggressive, it is fiction, and it is the most common reason a deal that penciled at $300 a month delivers nothing. Assuming 5% in a market where tenants move every year is a slower version of the same mistake. The test is simple: if a listing only works at 3%, you do not have a deal, you have a hope with a mortgage attached.
The rental property analyzer runs the full stack on an active listing — rent against taxes, insurance, maintenance, capex, management, and the vacancy rate you choose — so you can watch cash flow move as you tighten the assumption. Then check what it does to your money with the cash-on-cash calculator, because vacancy hits the return on your down payment harder than the monthly number. Rules on notice, entry, and showings vary by state, so confirm the local specifics with a professional.
Vacancy is unusual among operating expenses in that you can manage most of it away. Taxes arrive whether you are good at this or not, and insurance does not care how fast you answer the phone. But the gap between leases is almost entirely price, condition, photos, response speed, and how early you started — and every week you take out of it is about $325 on a $1,400 unit that you simply keep. Treat it as an operating discipline rather than weather, and it stops being the line that eats your year.
Three listings from the catalog right now, underwritten with vacancy, maintenance, and management already subtracted — not rent minus mortgage. Open any of them and check the numbers yourself.
