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
Applies a regional labor-and-bid multiplier to the whole job.
Result
Conversion cost
$132,250
Net rent per year
$12,946
Years to pay back
10.2
Annual return on the conversion
9.8%
Code and compliance items
$23,500
Kitchen and bathroom
$32,000
Contingency reserve
$17,250
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How to use this
- 1Enter basement area to convert (sq ft).
- 2Enter finish rate ($/sq ft).
- 3Enter region — Applies a regional labor-and-bid multiplier to the whole job..
- 4Enter egress window and separate entrance ($).
- 5Enter kitchen ($).
- 6Enter full bathroom ($).
- 7Enter separate heating and cooling ($).
- 8Enter fire separation, permits and inspections ($).
- 9Enter contingency (%).
- 10Enter expected rent ($/mo).
- 11Enter vacancy allowance (%).
- 12Enter operating costs (utilities, repairs, turnover) (% of rent).
- 13Read your conversion cost on the right — it updates as you type.
- 14Hit Share to keep the scenario or send it to someone.
About this calculator
A basement apartment is one of the few renovations that pays you back, but only if it is legal, and legality is where the budget lives. A rentable unit needs egress, a separate entrance in most jurisdictions, fire separation between units, a kitchen, a full bathroom, its own heat, and often a permit that triggers a parking or utility requirement. This calculator prices the finish per square foot with a regional index, itemises the code items separately so you can see how much of the budget is compliance rather than comfort, then converts the monthly rent into a payback period after vacancy and operating costs. Worked assumption for the defaults: 700 sq ft at $85/sq ft, $12,000 egress and entrance, $18,000 kitchen, $14,000 bathroom, $6,500 separate HVAC, $5,000 fire separation and permits, 15% contingency, renting at $1,450 with 7% vacancy and 20% operating costs — about $132,000 in and roughly 10.2 years to pay back.
Worked example
Using the values the calculator loads with:
Inputs
- Basement area to convert: 700 sq ft
- Finish rate: 85 $/sq ft
- Region: US national average — 1.00×
- Egress window and separate entrance: 12000 $
- Kitchen: 18000 $
- Full bathroom: 14000 $
- Separate heating and cooling: 6500 $
- Fire separation, permits and inspections: 5000 $
- Contingency: 15 %
- Expected rent: 1450 $/mo
- Vacancy allowance: 7 %
- Operating costs (utilities, repairs, turnover): 20 % of rent
Results
- Conversion cost: $132,250
- Net rent per year: $12,946
- Years to pay back: 10.2
- Annual return on the conversion: 9.8%
- Code and compliance items: $23,500
- Kitchen and bathroom: $32,000
- Contingency reserve: $17,250
What each field means
Inputs
- Basement area to convert (sq ft)
- The basement area to convert used in the calculation, measured in sq ft. Starts at 700 sq ft so you have a working example on load. Accepted range: 200–2500 sq ft.
- Finish rate ($/sq ft)
- The finish rate used in the calculation, measured in $/sq ft. Starts at 85 $/sq ft so you have a working example on load. Accepted range: 40–250 $/sq ft.
- Region
- Applies a regional labor-and-bid multiplier to the whole job.
- Egress window and separate entrance ($)
- The egress window and separate entrance used in the calculation, measured in $. Starts at 12000 $ so you have a working example on load. Accepted range: 0–60000 $.
- Kitchen ($)
- The kitchen used in the calculation, measured in $. Starts at 18000 $ so you have a working example on load. Accepted range: 0–90000 $.
- Full bathroom ($)
- The full bathroom used in the calculation, measured in $. Starts at 14000 $ so you have a working example on load. Accepted range: 0–70000 $.
- Separate heating and cooling ($)
- The separate heating and cooling used in the calculation, measured in $. Starts at 6500 $ so you have a working example on load. Accepted range: 0–40000 $.
- Fire separation, permits and inspections ($)
- The fire separation, permits and inspections used in the calculation, measured in $. Starts at 5000 $ so you have a working example on load. Accepted range: 0–40000 $.
- Contingency (%)
- The contingency used in the calculation, measured in %. Starts at 15 % so you have a working example on load. Accepted range: 0–35 %.
- Expected rent ($/mo)
- The expected rent used in the calculation, measured in $/mo. Starts at 1450 $/mo so you have a working example on load. Accepted range: 0–8000 $/mo.
- Vacancy allowance (%)
- The vacancy allowance used in the calculation, measured in %. Starts at 7 % so you have a working example on load. Accepted range: 0–40 %.
- Operating costs (utilities, repairs, turnover) (% of rent)
- The operating costs (utilities, repairs, turnover) used in the calculation, measured in % of rent. Starts at 20 % of rent so you have a working example on load. Accepted range: 0–60 % of rent.
Results
- Conversion cost
- 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.
- Net rent per year
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Years to pay back
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Annual return on the conversion
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Code and compliance items
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Kitchen and bathroom
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Contingency 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
Is a basement apartment legal where I live?
It depends entirely on local zoning and code — ceiling height, egress, separate entrance, and whether accessory units are permitted at all. Ask the building department before you spend anything; an illegal unit is uninsurable and can be ordered closed.
Why does the payback ignore appreciation?
Because rent is the cash you can count on and appreciation is not. A legal unit usually adds value at sale too, which makes the real payback shorter than shown — treat this figure as the conservative floor.
Where does the regional multiplier come from?
It is a job-level index against a US national average of 1.00, built from the spread contractors quote between low-cost rural markets and the highest-cost coastal metros. Materials vary less than labor, but bids move together, so one index tracks real quotes better than splitting them. Swap in your own multiplier by picking the tier closest to two bids you already have.
Why does the tool add a contingency?
Because renovation scopes change once walls are open. On finished-space work 10–15% is normal; on anything touching foundations, sewer lines, or 1970s-and-older wiring, 20% is the honest number. If your contingency is never spent, you finished under budget — that is the point.
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). Cost to Convert a Basement to a Rental Apartment Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cost-to-convert-basement-to-rental-apartment-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cost-to-convert-basement-to-rental-apartment-calculator" target="_blank" rel="noopener">Cost to Convert a Basement to a Rental Apartment Calculator — RevenueLab</a> (2026).</p>
Source: [Cost to Convert a Basement to a Rental Apartment Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cost-to-convert-basement-to-rental-apartment-calculator) (2026).