Home Addition Value Calculator

A home addition has two numbers that matter: what it will cost you, and what it will add to the home’s value. Most calculators only answer the first. This one answers both, because an addition that costs $97,600 and adds $56,000 in value is a very different decision from one that breaks even.

Use the first tab to estimate the full project cost – construction plus the contingency and design/permit costs estimators leave out – and the value the addition recoups. Use the second tab to project a new home value from the current value and an expected percentage increase.

How to use the two modes

Cost + value starts with the addition type, which pre-fills a mid-range construction cost per square foot – edit it freely to match your quotes or your market. Enter the size, the percentage of the construction cost you expect to recoup in home value, and optional percentages for contingency and design/permits. The tool shows the construction cost, each add-on, the all-in project cost, the estimated added home value, and the net gain or loss against the all-in cost.

New home value takes the appraiser's approach: current home value, project cost, and the expected percentage increase in the home's value. It returns the projected new value, the dollars added, and the net gain after subtracting what the project costs.

The formulas

Construction cost = square feet × cost per square foot
All-in cost = construction × (1 + contingency% ÷ 100 + design and permit% ÷ 100)
Added home value = construction cost × recoup% ÷ 100
Net gain = added home value − all-in cost
New home value = current home value × (1 + increase% ÷ 100)

The "recoup" framing is deliberate: remodeling industry data consistently shows additions return a fraction of their cost in resale value, not the whole amount. Entering 70% means you expect $70,000 of value for every $100,000 of construction – the honest way to think about it.

Worked examples

Cost + value. A 400 sq ft bedroom addition at $200 per square foot: construction $80,000, plus a 10% contingency ($8,000) and 12% for design and permits ($9,600), for an all-in cost of $97,600 ($244 per sq ft all-in). If the project recoups 70% of construction cost in home value, the added value is $56,000 and the net position is −$41,600. That loss is normal – most additions are bought for the living space, not as investments.

New home value. A $400,000 home, a $50,000 addition, and a 12% expected value increase: new value $448,000, value added $48,000, net −$2,000 after the project cost. Nearly break-even on paper, plus whatever the extra space is worth to you while you live there.

Typical construction costs by addition type

Mid-range national figures for construction only, before design, permits, and contingency. Your market and finishes move these significantly.

Addition type	Typical range per sq ft	Mid-range default
Bedroom	$150 – $250	$200
Bathroom	$200 – $350	$275
Kitchen expansion	$250 – $400	$325
Sunroom	$120 – $200	$160
Garage conversion	$80 – $150	$135
Second story	$200 – $350+	$275
In-law suite / ADU	$150 – $400	$275

As a rule of thumb, a mid-range ground-floor addition runs roughly $150–$330 per square foot for construction in recent national data, while second-story work runs $260–$480 because the existing structure must carry the new floor. Small additions cost more per square foot – fixed costs like the foundation tie-in and permits spread over fewer feet.

What competing tools miss

Every cost calculator I read answers "what will it cost" in increasing levels of detail – from a single square-footage multiplication to full engineering models with foundation types, HVAC approaches, and regional multipliers. What none of them answer is the question in this page's keyword: what is it worth? They leave you with a cost and no way to judge whether the project makes financial sense.

This page keeps the cost side honest – type-based rates, contingency shown separately the way professional estimators do it, design and permits itemized rather than hidden – and adds the missing half: the recouped value, the net gain against the all-in cost, and a second mode that projects the new home value directly. An addition estimate without the value side is only half a decision.

FAQs

How much does a home addition cost per square foot?
Recent national data puts a mid-range ground-floor addition at roughly $150–$330 per square foot for construction, and second-story work at $260–$480. Design, engineering, and permits typically add another 7–20% on top, and a contingency reserve of 10–20% is standard practice.

What does value recouped mean?
The share of the project cost that comes back as home value. A 70% recoup on an $80,000 addition means the home is worth about $56,000 more afterward. Recoup rates below 100% are normal – the annual Cost vs. Value report published by Remodeling Magazine tracks these by project type and market.

Which additions add the most value?
Broadly, functional space – bedrooms and bathrooms that bring a home in line with neighborhood norms – recoups better than highly personalized or luxury work. But the real answer is local: an addition is worth what comparable homes with that feature sell for in your market, so check recent comparable sales before trusting any national percentage.

Should I include a contingency?
Yes. Ten percent is a common minimum; older homes and projects that open up existing walls deserve 15–20%. Contingency is money you set aside for hidden conditions, not part of the quoted cost – which is why the calculator shows it as a separate line.

Do I need permits for an addition?
Virtually always. Building, electrical, plumbing, and mechanical permits are typically required for anything that expands the footprint or alters the structure, usually costing 0.5–2% of construction value. Impact fees for new dwelling units like ADUs can run far higher and are set locally.

Is it cheaper to build up or out?
Building out is usually cheaper per project because you avoid reinforcing the existing structure, but it consumes yard space and can hit setback limits. Building up reuses the foundation but pays for structural reinforcement and roof work – which is why second-story additions run $260–$480 per square foot.

Will an addition raise my property taxes?
Almost certainly. The assessor will eventually capture the added square footage and value, raising your tax bill. That ongoing cost is not part of a construction estimate, so budget for it separately.

How do I estimate the value increase percentage?
The best method is comparable sales: what do similar homes with and without this feature sell for in your area? A local appraiser can give a pre-renovation opinion, and Remodeling Magazine's Cost vs. Value report publishes recoup rates by project as a starting point. When in doubt, estimate conservatively.