Rental Arbitrage: What the Numbers Actually Need to Say Yes

Rental arbitrage gets pitched as a data question: will this work in a given market? That's the second question. The first one is whether the spread has enough margin to survive a bad month, because unlike owning the property, there's no equity cushion underneath you if it doesn't.

What arbitrage math actually requires

Arbitrage means signing a lease as a tenant, then subletting the unit short-term. Three numbers decide whether it works.

Rent

Fixed the moment you sign. It doesn't move with a slow month, a soft season, or a market that underperforms your projection — it's the one number in this entire calculation that has no flexibility at all.

STR-specific costs

These sit on top of rent and don't exist for a normal tenant: furnishing the unit, cleaning between every guest instead of once a year, platform fees on every booking, and a higher utility load than a landlord would plan for from a long-term renter. Skipping this category is the most common way an arbitrage projection ends up too optimistic — it's easy to compare revenue against rent alone and miss everything else a short-term operation adds on top.

Projected revenue

What the unit actually books, based on realistic rate and occupancy for the specific market and unit type — not the best month you can imagine, and not a number pulled from a market average that doesn't match your specific property.

The spread is revenue minus rent minus STR-specific costs. That's the number that has to work — not revenue alone, and not revenue minus rent without the extra costs a normal lease never had to account for.

The margin has to survive a bad month, not just an average one

Say the rent is $2,500 a month. STR-specific costs — furnishing amortized over a year, cleaning, platform fees, the extra utility load — run about $400 a month. Average-case projected revenue is $4,200 a month. On paper, that's a spread of $1,300 a month: $4,200 minus $2,500 minus $400.

Now say occupancy comes in 20% below projection for two months, which is a realistic stretch, not a worst case. Revenue drops roughly in proportion to occupancy, so a 20% shortfall on $4,200 is about $840 gone. Costs don't move — rent is still $2,500, STR costs are still roughly $400. The margin that looked like $1,300 is now closer to $460, and if the shortfall runs deeper or longer, it goes negative. Rent is still due either way.

This is the part ownership doesn't have to deal with the same way. A property that has a bad quarter still has equity sitting underneath it. A lease has none. The entire position is the spread, every month, with nothing to fall back on if it goes the wrong way — which is why the number worth checking isn't the average-case spread, it's what the spread looks like under a realistic bad stretch.

What the lease has to allow

None of the arithmetic matters if the lease doesn't permit it. Subletting for short-term rental has to be explicitly allowed — silence in a lease is not permission, and plenty of standard leases prohibit subletting entirely or cap stays well above a nightly rental. Local rules on subletting for STR vary by city and sometimes by building, separate from whatever the lease itself says. And a landlord's verbal comfort with the idea isn't the same as it being written into the agreement.

This is the single most common way an arbitrage deal fails, and it fails before the financial math is even relevant. Confirm the lease and local permissions first. A spread that pencils out on a unit you can't legally sublet isn't a deal, it's a number on a page.

The short version

• The spread is revenue minus rent minus STR-specific costs, not revenue minus rent alone — furnishing, per-guest cleaning, platform fees, and extra utilities all sit outside what a normal tenant pays.
• Check the margin under a bad stretch, not the average case. Rent doesn't drop with a slow month. A spread that only works at projected occupancy isn't a real margin.
• There's no equity cushion. A bad month in an owned property still leaves you holding an asset. A bad month in a lease is just a loss, with nothing underneath it.
• Confirm the lease allows it before anything else. Subletting has to be explicit, and local rules add a second layer on top of what the lease says.
• None of this needs market data to check. It's arithmetic on your specific rent and costs — the market only tells you what revenue to project, not whether the structure holds.

Run your own spread

The revenue side of this only matters once you know your actual rent and costs. Pull realistic rate and occupancy figures for a market you're considering from Market Analysis, then run them against your real rent and STR-specific costs in the Revenue Calculator — that's what turns this from a projection into a number you can actually check against a bad month, not just an average one.