Cash Flow per Unit Calculator
The formula
What the mailbox money, measured tells you
The per-door monthly surplus after real vacancy, opex, debt and the reserve line most pro forms include and amateur forms skip.
Calculation: Per-door cash flow = rent − opex − debt − reserves, after vacancy. Enter your inputs and every substitution is shown below the result.
Reading the result
1,650 rent against 1,245 of true costs is 305/door — 14.6k a year on four doors, boring and compounding.
Rules of thumb: Underwrite 5–10% vacancy + 2% reserves of EGI
Limitations and best practice
Quoting cash flow before reserves converts every big-ticket year into a surprise special call.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Reserves how much?
Why 94% collection?
Levered vs unlevered?
Source & methodology
Multifamily underwriting norms (IREM).
Cash Flow per Unit explained: formula, worked example and honest limits
This page was written for one job: turning your own inputs into a defensible figure, with the working shown. Cash Flow per Unit is the kind of number people argue about from memory. This page ends that argument with arithmetic you can watch happen: enter your figures, get Cash flow per unit in real time, and see every substitution printed below.
Leverage is the distinctive physics of Real Estate & Property: borrowed money amplifies both directions of return. When you compute Cash Flow per Unit, remember the inputs involving financing (down payment, rate) are not cosmetic — they can dominate the operating reality captured in Rent/unit/mo ($).
What makes Cash Flow per Unit worth calculating is not precision but position: it tells you which side of a threshold you are on, and by how much. A rough figure that settles the direction beats an elaborate one that never commits.
Nothing below is stock text pasted around a number: the worked example computes cash flow per unit = $83.00 from this tool’s own defaults, and the sensitivity section ranks the inputs that move the result — Rent/unit/mo first, at ≈277.5 % of the headline for a ten-percent error either way in that input. Work down the page and by the end you could re-derive the result in a spreadsheet from memory.
How Cash Flow per Unit is computed, line by line
The engine implements a single stated model: Per-door cash flow = rent − opex − debt − reserves, after vacancy. There is no hidden coefficient and no login-gated precision — the formula printed is the formula executed, which is also what makes the result citable.
Rent/unit/mo ($) (example value 2,450) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Count from the record, not the estimate; whole-number inputs are cheap to verify and expensive to get wrong.
Units (example value 9) is a plain measured quantity — the unit shown in the label is the unit the formula expects. If the true figure falls between counts, run both and read the spread as your uncertainty.
Monthly opex/unit ($) (example value 695) is a quantity rather than a category — precision here is cheap and worth having. Count from the record, not the estimate; whole-number inputs are cheap to verify and expensive to get wrong.
Monthly debt service/unit ($) (example value 1,425) is a quantity rather than a category — precision here is cheap and worth having. If the true figure falls between counts, run both and read the spread as your uncertainty.
Reserves/unit/mo ($) (example value 100) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Count from the record, not the estimate; whole-number inputs are cheap to verify and expensive to get wrong.
Cash Flow per Unit with real numbers, step by step
The tool prints its own working; this is the same arithmetic on the example values, reproduced so you can follow it by hand. Starting figures: Rent/unit/mo ($), Units, Monthly opex/unit ($), Monthly debt service/unit ($). The computed cash flow per unit comes out at $83.00, which the interpretation band labels “After true costs, $83.00/unit lands $8,964/yr at the mailbox — before any appreciation”.
- Collected at 94% = $2,303
- − opex $695 − debt $1,425 − reserves $100
- = $83.00/door/mo
Annual per unit — $996. Compare it against the main result of $83.00 before drawing conclusions.
Whole property annual — $8,964. Read next to the headline, this is the figure that shows the shape of the trade-off.
Flow margin — 3.6 %. If your inputs change, this is usually the first companion figure to move.
Rent needed for +100/door — $2,320.00 gross. This is the number experienced users quote when the headline alone would mislead.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
Scenario table: Cash Flow per Unit at ±10 % and ±20 % of the key input
Read this table as the practical error bar on the headline figure. It answers the question people actually have after seeing a single number: how wrong could this be if the main input is off by ten or twenty percent?
| Rent/unit/mo setting | Cash flow per unit |
|---|---|
| 80 % of the example value | $-377.60 |
| 90 % of the example value | $-147.30 |
| example inputs | $83.00 |
| 110 % of the example value | $313.30 |
| 120 % of the example value | $543.60 |
The corridor runs from $-377.60 to $543.60 across that band — which is the range worth planning inside rather than the single $83.00 point estimate. Reproduce it in the form above by editing Rent/unit/mo alone; the substitution steps will follow your figures exactly.
What actually moves your Cash Flow per Unit
Nobody should have to guess which input matters. The engine was re-run once per field below — ten percent up, ten percent down, everything else frozen — and the results ranked by how far they moved the cash flow per unit. Read it as a map of where Cash Flow per Unit is fragile — drawn for the example inputs, which is the map you want when deciding what to measure carefully.
- Rent/unit/mo +10 % → Cash Flow per Unit = $313.30 · −10 % → $-147.30 (the cash flow per unit shifts ≈277.5 %)
- Monthly debt service/unit +10 % → Cash Flow per Unit = $-59.50 · −10 % → $225.50 (the cash flow per unit shifts ≈171.7 %)
- Monthly opex/unit: ten percent up gives $13.50, ten percent down gives $152.50 — ≈83.7 % of the cash flow per unit either way
- Reserves/unit/mo: ten percent up gives $73.00, ten percent down gives $93.00 — ≈12.0 % of the cash flow per unit either way
Rent/unit/mo is the dominant lever here: ten percent either way moves the result by about 277.5 %, from $-147.30 to $313.30. Spend your verification effort there first, and treat Monthly debt service/unit as the second priority (≈171.7 % per ten percent). The rest of the inputs earn only a rounding-error of attention, and that asymmetry is the practical payoff of measuring rather than asserting.
Is your Cash Flow per Unit good — reading the result bands
The value above only becomes useful the moment you know what it is being measured against. The verdict attached to the default calculation — “After true costs, $83.00/unit lands $8,964/yr at the mailbox — before any appreciation” — is one band on a ladder your own figure may sit somewhere else on. Before treating the band as fact, note its width: ten percent either way on Rent/unit/mo already spans $-147.30 to $313.30. The practical reading rules: ask what would have to change to move you one band. If the answer is “a small, plausible input difference”, the band itself is not the finding — the uncertainty is.
Where Cash Flow per Unit sits next to similar measures: this tool answers “how much is the Cash Flow per Unit”, while the related calculators answer “what do I do about it”. Reading the result alone tends to over-weight a single snapshot; pairing it with the companion tools above turns the number into a decision.
Why Cash Flow per Unit results go wrong — and how to prevent it
Quoting cash flow before reserves converts every big-ticket year into a surprise special call. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Using stale inputs. Cash Flow per Unit is only as current as the numbers behind it — an estimate carried over from a previous season, rate table or report quietly biases every output. Re-measure the inputs first; that single habit fixes more bad Cash Flow per Unit figures than any formula change.
One mistake is specific to this engine: assuming every input matters equally. The computation above shows Rent/unit/mo dominating — a careful figure there beats false precision everywhere else.
A final trap is presentation: reporting Cash Flow per Unit to more decimal places than the inputs support. The tool prints what the arithmetic gives; you should quote only what your least precise field justifies.
Six things to confirm before acting on Cash Flow per Unit
- State, in one sentence, which convention each rate, unit or period in the form is using.
- Compare the output against one published benchmark or a colleague’s independent estimate.
- Put Rent/unit/mo under a magnifier; the sensitivity table above is the reason why.
- Record the date and the inputs alongside the number so future-you knows what was assumed.
- Note the date and the inputs beside the number so the figure can be audited later.
- Confirm the answer against one independent method or published benchmark for Cash Flow per Unit.
A routine for decision-grade Cash Flow per Unit
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — start from evidence. The inputs behind Cash Flow per Unit are rent/unit/mo ($), units, monthly opex/unit ($), monthly debt service/unit ($), reserves/unit/mo ($). Write them down with their source next to each one; if you cannot name where a figure came from, that is the input most likely to be wrong. Numbers are cheap to produce and expensive to retract; the extra minute is the cheapest insurance available.
Step 2 — enter the conservative case first. Resist the flattering scenario. Type the inputs you would defend in front of a sceptical reader, read the Cash flow per unit ($83.00 for the example values), and note the verdict band. A calculation you cannot explain to somebody else is a calculation you cannot defend.
Step 3 — play with the inputs on purpose. Ten percent up, ten percent down, one field at a time. Within a few minutes you will know this calculation better than most people who quote its results. The input you reach for first is usually the one you measured longest ago.
Step 4 — stress before you commit. A decision that survives a ten-percent squeeze on its two biggest inputs needs no luck to be sound. One that does not survive is a decision about hope, not about arithmetic. The inputs are the part of the work that nobody else can do for you.
Step 5 — write the one-line memo. “Cash flow per unit = $83.00 on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. Precision is a promise you make about your data; make sure your inputs can keep it.
From calculation to decision: where Cash Flow per Unit earns its keep
In Property Management the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Write the figure down before moving on; memory flatters whichever number you saw last.
Professionals in Property Management use this style of calculation as a screening filter before spending real money or effort: a quick Cash Flow per Unit check eliminates weak options in minutes, and the survivors earn the deeper, slower analysis. If the verdict changes with a ten-percent nudge, report the nudge alongside the number.
Re-running this page costs nothing and catches the slow drifts that never announce themselves. In Real Estate & Property the expensive mistakes are rarely sudden; they are small changes in Rent/unit/mo ($) that nobody recalculated for a year. Precision is a promise you make about your data; make sure your inputs can keep it.
Cash Flow per Unit — frequently asked questions
What affects Cash Flow per Unit the most?
The short answer: Rent/unit/mo. The longer answer is the sensitivity table on this page, where every numeric input was probed by ten percent and the cash flow per unit recalculated — Rent/unit/mo moved it furthest, by roughly 277.5 % ($-147.30 to $313.30).
Which matters more: monthly debt service/unit or rent/unit/mo?
For Cash Flow per Unit, Rent/unit/mo wins the head-to-head (≈277.5 % against ≈171.7 % per ten-percent change). Knowing which input dominates is the difference between careful work and merely slow work.
What is a typical Cash Flow per Unit?
With the example inputs on this page the result is $83.00, labelled “After true costs, $83.00/unit lands $8,964/yr at the mailbox — before any appreciation”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Cash Flow per Unit by hand?
Use the stated model — Per-door cash flow = rent − opex − debt − reserves, after vacancy — and substitute in the order the tool prints (it starts from Collected at 94% = $2,303). On the example inputs the hand route lands on $83.00, exactly what the calculator shows. A spreadsheet reproduces it in two or three cells; doing it once by hand is what makes the automated answer trustworthy.
What happens to Cash Flow per Unit if rent/unit/mo changes by 10 %?
On these inputs a ±10 % change in rent/unit/mo takes Cash Flow per Unit to $313.30 against the $83.00 example — around 277.5 % of the headline. The same test on every other field is in the sensitivity section.
Is the Cash Flow per Unit result of $83.00 good or bad?
Good and bad are comparisons, so the honest test is three questions: where does your own Cash Flow per Unit sit against the $83.00 reference above, how far would a plausible input error move it (≈277.5 % per ten percent on Rent/unit/mo), and what does the alternative option compute to?
Which costs are missing from Cash Flow per Unit?
Vacancy, management, capital reserves and closing amortisation are the usual absentees. The tool computes what you feed it; adding those into the expense side moves the number from marketing to operations.
Is $83.00 good for this property?
Goodness is comparative: run the same Cash Flow per Unit across several candidates and rank. Absolute thresholds exist by region and product type, so pair the verdict band here with a quick survey of the Property Management comps you can actually access.
Reserves how much?
75–150/door/month for apartments; roof-structure-paving weighted by age.
Why 94% collection?
6% vacancy/credit loss is the stabilized convention; class-C runs 10%+.
Does this Cash Flow per Unit tool store my numbers?
No. The entire calculation runs in your browser session; nothing entered above is transmitted or saved, which is the correct behaviour for sensitive Real Estate & Property figures and the reason you can re-run this page as often as you like.
The vocabulary of Cash Flow per Unit
- Annual per unit
- $996 for the Cash Flow per Unit worked case; it sits next to the main result because it carries context the headline leaves out.
- Whole property annual
- $8,964 for the Cash Flow per Unit worked case; it sits next to the main result because it carries context the headline leaves out.
- Flow margin
- 3.6 % on the example inputs — a companion figure printed beside the headline of Cash Flow per Unit so that no result is read in isolation.
- Cash flow per unit
- The primary output of this tool: $83.00 for the default inputs, computed exactly from Per-door cash flow = rent − opex − debt − reserves, after vacancy.
- Worked example
- Every substitution in order, from the example inputs to $83.00 — the audit trail for the headline figure.
- Verdict band
- The interpretation attached to a result (“After true costs, $83.00/unit lands $8,964/yr at the mailbox — before any appreciation” on these inputs), which turns a bare number into a position on a scale.
- Sensitivity (±10 %)
- How far the Cash Flow per Unit moves when a single input is nudged ten percent either way; the ranked list on this page is computed live from this engine.
Where the Cash Flow per Unit model comes from
There is no black box on this page — the engine evaluates Per-door cash flow = rent − opex − debt − reserves, after vacancy. Source of record: Multifamily underwriting norms (IREM). Any other implementation of this model should return the same figure for the same inputs. If one does not, the difference is in its assumptions — which this page prints and that one probably does not.
Treat the output as a precise answer to the question you typed: exact arithmetic, transparent formula, published source, no hidden rounding. The design constraint was set by usefulness rather than by comfort: an estimate you can interrogate beats an answer you have to trust.
Next steps after the calculation
Re-run the calculation with your own figures, stress the two most sensitive inputs by ±10 %, and only then act on the result.
The audience here is people who need one trustworthy number before their next decision. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.