ADU Calculator

Second Unit Basics

Where will your Second Unit be built?

Type of construction

New construction includes both attached
and detached second units.

Conversion of part of house means
taking existing living space, e.g. a
basement or part of the house, and
turning it into a second unit.

Modular/panelized are built partially
or entirely off site and delivered
to the property. ?

Number of Bedrooms

If you change the number of bedrooms,
be sure to adjust the square footage accordingly ?

Number of Bathrooms

Heating system

Plumbing system

Electrical system

Kitchen plans

Square feet

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{{myForm.ADUSqft.$viewValue}} is below 150 sqft minimum

{{myForm.ADUSqft.$viewValue}} is above maximum sqft of {{ADUSqftMax}} in {{cityName}}

sqft

Unit sizes vary significantly,
but typical square footage is:
Studio : 400 sqft

1 Bedroom : 600 sqft
2 Bedroom : 800 sqft
3 Bedroom : 1,200 sqft ?

Interior quality

Different levels of interior quality
(e.g. countertops, flooring, etc.) affect
the final construction price. Please choose
the interior quality that best matches your
planned construction.

Low cost: Rental quality. Entry level
appliances, low cost carpet, etc.

Standard: Typical for San Mateo County,
which means generally high quality. Stainless
steel appliances, solid countertops, a mix of
carpet and hardwood or tile.

High cost: Assumes the top end of anything
generally available at major retailers, ceramic
tile floors, etc. Costs would be higher if, for
example, you used a custom cabinet maker. ?

Do you want to estimate the construction cost or let the calculator do it?

Estimate total construction cost

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{{myForm.ConstructionCost.$viewValue}} is below $50,000 minimum

{{myForm.ConstructionCost.$viewValue}} is above $700,000 max

Site conditions / construction difficulty

Individual site conditions can significantly
affect construction cost. The most common
reason construction is more expensive is
building on a hillside, but there are
many other potential challenges. ?

Rent and Financing

Do you plan to take out a loan?

Loan Length

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{{myForm.LoanTerm.$viewValue}} is below 1 year minimum

{{myForm.LoanTerm.$viewValue}} is above 30 year max

years

Typical loans are 20 years or less. ?

Interest rate

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{{myForm.LoanInterestRate.$viewValue}} is above 7% max

Check with your local bank for today's rates ?

Cash Investment

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${{myForm.CashInvestment.$viewValue}} exceeds the ${{CashInvestmentMax}} construction costs

Rents: Do you want to…

Consider pricing your unit so a teacher or
nurse can afford it. You'll be helping the
community and they make great tenants! ?

Enter rent here

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{{myForm.Rent.$viewValue}} is below $700 minimum

{{myForm.Rent.$viewValue}} is above $7,115 max

Once it is built, will you hire someone to manage it?

Managing a second unit means finding a
tenant and doing repairs as necessary.
Typical costs to hire someone for
this are 5% of the rent. ?

Increased value

There have not been enough second units
built to accurately estimate how much
it is likely to increase the value of
a house. The calculator assumes the
increase will be a multiple of the
rent. See assumptions below ?

Increased value

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{{myForm.IncreasedValue.$viewValue}} is above 600,000 max

Advanced Features

Simple or Advanced

How fast will rents go up per year?

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{{myForm.RentInflation.$viewValue}} is below 1% minimum

{{myForm.RentInflation.$viewValue}} is above 10% max

What is your tax rate?

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{{myForm.TaxRate.$viewValue}} is below 1% minimum

{{myForm.TaxRate.$viewValue}} is above 1.5% max

Look up your tax rate at
www.sanmateocountytaxcollector.org ?

Insurance cost (as a percent of replacement cost)

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{{myForm.InsuranceRate.$viewValue}} is above 1% max

How long do you expect the average tenant to live in the Second Unit? (years)

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{{myForm.YearsOccupied.$viewValue}} is below 1 year minimum

{{myForm.YearsOccupied.$viewValue}} is above 120 year max

years

How long do you expect it to take to find a new tenant?

Required message

{{myForm.WeekstoOccupy.$viewValue}} is above 8 week max

weeks

If using a management company, management costs (% of rent). Otherwise enter 0.

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{{myForm.ManagementRate.$viewValue}} must be above 0% minimum

{{myForm.ManagementRate.$viewValue}} is above 10% max

There is an unexpected number in
the information you've provided. Please review and update to see results.

Results

Monthly Income After Expenses

{{Rent | currency : usd : 0}}monthly rent and {{MonthlyCosts[0] | currency : usd : 0}} monthly costs

Hover over chart for monthly cost breakdown

${{TotalDevelopmentCostShort}}K

Construction Costs

The cost to build your Second Unit is estimated at {{TotalDevelopmentCost/ADUSqft | currency : usd : 0}} per square foot with a total cost of {{TotalDevelopmentCost | currency : usd : 0}}.

Hover over chart for construction cost breakdown. Hard costs cover constructing the second unit, both labor and materials. Soft costs are things like architects. Fees are charged by the city.

Years to earn back your cash investment

You will recover your initial cash investment of {{CashInvestment | currency : usd : 0}} in {{YearsInvestmentRecovered | number : 0}} years (excluding outstanding loan balance and increased value of house).

Year Return on Investment

Once you account for the amount remaining on your loan and the increase in property value, your Second Unit will pay for itself in {{YearsADURecovered | number : 0}} years.

${{IncreasedValueShort}}K

Increase in Home Value

Your Second Unit will increase your home value by approximately {{IncreasedValue | currency : usd : 0}}, assuming the value increases by 8-9 times the yearly rent.

Year 10

Year 20

Year 30

Property value increase
from second unit

Rent collected (cumulatively)

Cumulative net income
(rents minus costs)

Future monthly rents

Monthly costs

Annual tax increase

Average annual return on investment (just using rent)

{{(GrossRentalRevenue[4]/12 - MonthlyCosts[4]) / CashInvestment * 100 | number : 1}}%

{{(GrossRentalRevenue[9]/12 - MonthlyCosts[9]) / CashInvestment * 100 | number : 1}}%

{{(GrossRentalRevenue[19]/12 - MonthlyCosts[19]) / CashInvestment * 100 | number : 1}}%

{{(GrossRentalRevenue[29]/12 - MonthlyCosts[29]) / CashInvestment * 100 | number : 1}}%

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ADU Calculator

Second Unit Basics

Rent and Financing

Advanced Features

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