Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Recommended reserve per door
$78.82
Per door, annualized
$946
Total annual reserve needed
$9,458
Roof component of reserve
$1,833
HVAC component of reserve
$5,625
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How to use this
- 1Enter number of units.
- 2Enter roof replacement cost ($).
- 3Enter roof remaining useful life (years).
- 4Enter hvac replacement cost (total, all units) ($).
- 5Enter hvac remaining useful life (years).
- 6Enter other systems (parking, siding, appliances) total cost ($).
- 7Enter other systems avg remaining life (years).
- 8Read your recommended reserve per door on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Operating reserves cover routine repairs; a capital expenditure reserve covers the big items that fail on a schedule measured in years, not months — roofs, HVAC systems, water heaters, parking lots, siding. This calculator uses the component-based method appraisers and lenders prefer: take each major system's replacement cost, divide by its remaining useful life, and sum the annual amounts, then divide by unit count and 12 for a per-door monthly reserve. This is more defensible than a flat percentage-of-rent rule because it's tied to your building's actual age and systems rather than a generic assumption that ignores whether you have a 3-year-old roof or one that's 22 years into a 25-year life.
Worked example
Using the values the calculator loads with:
Inputs
- Number of units: 10
- Roof replacement cost: 22000 $
- Roof remaining useful life: 12 years
- HVAC replacement cost (total, all units): 45000 $
- HVAC remaining useful life: 8 years
- Other systems (parking, siding, appliances) total cost: 30000 $
- Other systems avg remaining life: 15 years
Results
- Recommended reserve per door: $78.82
- Per door, annualized: $946
- Total annual reserve needed: $9,458
- Roof component of reserve: $1,833
- HVAC component of reserve: $5,625
What each field means
Inputs
- Number of units
- The number of units used in the calculation. Starts at 10 so you have a working example on load.
- Roof replacement cost ($)
- The roof replacement cost used in the calculation, measured in $. Starts at 22000 $ so you have a working example on load.
- Roof remaining useful life (years)
- The roof remaining useful life used in the calculation, measured in years. Starts at 12 years so you have a working example on load. Accepted range: 1–40 years.
- HVAC replacement cost (total, all units) ($)
- The hvac replacement cost (total, all units) used in the calculation, measured in $. Starts at 45000 $ so you have a working example on load.
- HVAC remaining useful life (years)
- The hvac remaining useful life used in the calculation, measured in years. Starts at 8 years so you have a working example on load. Accepted range: 1–30 years.
- Other systems (parking, siding, appliances) total cost ($)
- The other systems (parking, siding, appliances) total cost used in the calculation, measured in $. Starts at 30000 $ so you have a working example on load.
- Other systems avg remaining life (years)
- The other systems avg remaining life used in the calculation, measured in years. Starts at 15 years so you have a working example on load. Accepted range: 1–40 years.
Results
- Recommended reserve per door
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Per door, annualized
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total annual reserve needed
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Roof component of reserve
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- HVAC component of reserve
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does this differ from the flat 5-10% of rent rule?
The flat percentage rule is a rough shortcut that ignores building age and system condition entirely — a newly renovated building and one with a 20-year-old roof shouldn't reserve the same percentage. The component method ties the reserve to what's actually aging in your specific property, which is what lenders and serious buyers expect to see in underwriting.
What if I don't know remaining useful life?
Get a property condition assessment (PCA) or ask a contractor to estimate remaining life during an inspection — asphalt shingle roofs typically run 20-25 years, HVAC condensers 12-18 years, and water heaters 8-12 years. When in doubt, be conservative and assume less remaining life, not more.
Should the reserve sit in a separate account?
Yes. Commingling reserves with operating cash is the single most common reason landlords get blindsided by a $15,000 roof bill — the money looks available in the operating account until the day you actually need it for something else.
Does a HUD or agency loan require a minimum reserve?
Yes — many agency multifamily loans (Fannie Mae, Freddie Mac) require a minimum funded replacement reserve, often $200-$300 per unit per year as a floor, adjusted upward based on a physical needs assessment for older properties.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). CapEx Reserve Per Door Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/capex-reserve-per-door
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/capex-reserve-per-door" target="_blank" rel="noopener">CapEx Reserve Per Door Calculator — RevenueLab</a> (2026).</p>
Source: [CapEx Reserve Per Door Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/capex-reserve-per-door) (2026).