Break-even occupancy: the 91.49% number that tells you how much bad luck a rental can take
Break-even occupancy is the share of the year a rental must be rented to cover every operating bill, reserves and the mortgage. Divide fixed expenses plus annual debt service by gross potential rent after percentage-based reserves. In our engine run, a $210,000 house that cash flows on paper needed 91.49% occupancy, leaving about a month of vacancy slack a year.
Here's a rental that passes. Purchase price $210,000, rent $1,850 a month, a normal 25% down loan, sensible reserves. It cash flows. Positive every month, on paper.
Now the uncomfortable question. How many more days a year can that house sit empty, past the vacancy you already budgeted, before the positive turns negative?
About nine. That's roughly a month of total slack once you count the vacancy already in the budget.
Not nine weeks. Nine DAYS beyond the vacancy you already budgeted, about a month of slack in the whole year. One slow turnover, one tenant who leaves in November instead of May, and the year is gone. And nothing on the listing, the pro forma, or the cash flow line will warn you, because none of them are built to answer that question.
One number is. It's called break-even occupancy, and by the end of this post you'll be able to compute it on any deal you look at. We'd much rather you meet it now than in your second November as a landlord.
What break-even occupancy actually measures
Break-even occupancy is the share of the year your rental has to be rented and collecting just to cover EVERY bill and the mortgage. Below it, you're feeding the property. Above it, the property is feeding you.
Why does that matter more than cash flow? Because cash flow is a single forecast. It assumes your vacancy guess is right. Break-even occupancy tells you how wrong that guess can be before it costs you money, which is the thing you actually lose sleep over.
Think of it like the gas gauge on a long drive. Your cash flow says you'll arrive with a little fuel left. Break-even occupancy says how far the next gas station can be before you're walking.
The formula (the version that holds up)
Here's the form we use, and the one you'll want too:
Break-even occupancy = (fixed operating expenses + annual debt service) / (gross potential rent × (1 − reserve rate))
Three pieces, and each one earns its place:
Fixed operating expenses are the bills that arrive whether the unit is full or empty: property taxes, insurance, HOA dues, any utilities you pay, lawn care. A vacant house still gets a tax bill.
Annual debt service is twelve months of principal and interest. Your lender doesn't care that the tenant moved out either.
The reserve rate is the part most calculators get subtly wrong. Management, repairs and capital reserves are usually budgeted as a percentage of the rent you collect. If you collect less, you set aside less. So those costs shrink as occupancy drops, and the formula has to let them shrink. That's why they come off the bottom of the fraction instead of sitting in the top.
Gross potential rent is simply what the property would bring in rented every single day of the year: monthly rent times twelve.
One house, worked line by line
Let's run the deal from the top of this post. These are the inputs:
| Input | Value |
|---|---|
| Purchase price | $210,000 |
| Monthly rent | $1,850 |
| Loan | 25% down, $157,500 at 7.00% over 30 years |
| Property taxes | $230 a month ($2,760 a year) |
| Insurance | $110 a month ($1,320 a year) |
| Vacancy allowance | 6% |
| Management / repairs / capital reserves | 8% / 5% / 5% of collected rent |
Now the pieces of the formula:
| Piece | Arithmetic | Result |
|---|---|---|
| Fixed operating expenses | $2,760 taxes + $1,320 insurance | $4,080 |
| Monthly principal and interest | $157,500 at 7.00%, 30 years | $1,047.85 |
| Annual debt service | $1,047.85 × 12 | $12,574.22 |
| Gross potential rent | $1,850 × 12 | $22,200 |
| Reserve rate | 8% + 5% + 5% | 18% |
| Break-even occupancy | ($4,080 + $12,574.22) / ($22,200 × 0.82) = $16,654.22 / $18,204 | 91.49% |
So this house has to be rented 91.49% of the year just to stand still.
Your budget assumed 6% vacancy, which means 94% occupancy. The gap between what you planned (94%) and what you need (91.49%) is 2.51 percentage points. Multiply by 365 and you get about 9.2 days. That's your entire margin for error for the year!
Does the cash flow line agree? It does, and that's the point. At 94% occupancy the deal produces $14,075.16 of NOI, and after the capital reserve and the mortgage it leaves about $38.13 a month. Positive. Thin. Exactly the kind of deal that looks fine until it isn't.
Break-even rent: the same idea from the other side
Flip the question around. Instead of asking how full the house has to be, ask how low the rent can go at your planned 6% vacancy before cash flow hits zero. For this deal it's $1,800.53 a month.
Your rent is $1,850. Your cushion is about $49 a month. If the true market rent turns out to be $1,800, you just bought a break-even house. Same story, different lens, and it's worth looking at both before you write an offer.
The four inputs that move it most
Here's what we got when we changed one thing at a time on this exact deal, so you can see which of your inputs deserve the most attention:
| Change | Break-even occupancy | Monthly cash flow |
|---|---|---|
| As modeled (25% down, 7.00%) | 91.49% | $38.13 |
| Rate is 7.50% instead of 7.00% | 95.01% | −$15.28 |
| 20% down instead of 25% | 96.09% | −$31.73 |
| Management as a flat $139.12 a month (the same $1,669.44 a year as 8%) | 91.71% | $38.13 |
| Rent is $1,950 instead of $1,850 | 86.79% | $115.21 |
A few things jump out.
Financing moves it more than almost anything. Half a point of interest rate eats more than three and a half points of your occupancy margin! Five points less down payment pushes you past 96%, which in practice means ONE ordinary turnover puts you underwater. If you're comparing loan quotes, compute break-even occupancy at each one. It turns "a slightly higher rate" into a number you can feel.
Fixed costs hurt MORE than variable ones. Look at the management row. Same dollars per year, same $38.13 of monthly cash flow, and yet break-even occupancy got worse. Why? Because a flat fee doesn't shrink when the unit is empty. Any time you convert a percentage cost into a fixed one, you're trading flexibility for certainty, and this metric shows you the price.
Rent is the STRONGEST lever you have. An extra $100 a month drops the requirement under 87%! Which is why the rent comp you used deserves more scrutiny than any other input on the sheet.
The textbook shortcut, and why we don't use it
You'll often see break-even occupancy written as total operating expenses plus debt service, divided by gross potential rent. On this deal that gives 91.94%, close to our 91.49%.
Close, but built on a quiet assumption: it treats management, repairs and reserves as if they cost the same in an empty house as in a full one. They don't. On a thin deal, or a property with higher percentage-based costs, the gap gets bigger, and since this is a number you might use to say yes or no, you want the version that matches how the money ACTUALLY moves.
So what's a good number?
There isn't a universal pass mark, and anyone who gives you one without asking about your market is guessing. What matters is the distance between your break-even and the occupancy your market really delivers.
If similar rentals near you stay rented 96% of the year and your break-even is 80%, you have room to absorb a bad tenant, a long turnover, or a surprise repair. If your break-even is 92% in that same market, you're betting the year on everything going right. And if it's above 100%? The deal can't cover itself even with a tenant in it every day, no matter how good the cash flow forecast looks.
Set your own line, then hold every deal to it. That's what a buy box is for.
Where BuyBox fits
We compute break-even occupancy on every deal using the reserve-aware formula above, with fixed costs and percentage-based reserves kept separate so a flat fee and a percentage behave the way they should. Hover the number and the formula and every input behind it show up, so you can check the arithmetic YOURSELF instead of trusting it.
What it can't do is know your real numbers. The tax bill, the insurance quote, the rent your market will actually pay: those come from you, and the result is only as good as what goes in.
Frequently asked
Is break-even occupancy the same as break-even vacancy?
They're two sides of one coin. Break-even vacancy is simply 100% minus break-even occupancy. For this deal, a break-even occupancy of 91.49% means you can tolerate up to 8.51% vacancy before cash flow goes negative.
Should capital reserves really be in the formula?
Yes, absolutely! Roofs and furnaces fail on their own schedule, and leaving the reserve out just relabels a future repair as free money today. We count the capital reserve as part of what the rent has to cover, the same way the NOI vs. cash flow post treats it below the NOI line.
Does a lender look at this?
Lenders usually focus on DSCR, which asks a related question: how many times NOI covers the mortgage. This deal's DSCR is about 1.12. Break-even occupancy is the version that speaks in days and months, which is how vacancy actually shows up in your life.