Home Addition Cost Calculator
This free home addition cost estimator prices your type and size line by line, including foundation, systems and fees. Adjusted for your state.
- Prices reviewed September 2026
- Adjusted for all 50 states
- No sign-up to see your number
Step 1 of 4
Your addition
Size and type.
Labor costs differ a lot by state. This adjusts every line.
New finished floor area, not counting the existing house.
Type of addition
Foundation
Estimated addition cost
$113,900
$73,000 – $154,800
How we calculate your home addition cost
We price the project line by line: demolition, cabinetry or fixtures, finishes, labor, permits, and a contingency buffer. Every line has its own low and high unit price, so the range you see comes from real spread in the market, not a flat percentage. Labor is then adjusted by state, and materials move far less by location than labor does.
Unit prices are national benchmark ranges last reviewed September 2026. Treat the result as a planning number for setting a budget and judging contractor bids. It is not a quote. Read our full methodology.
What a home addition estimate includes
- Framing, roof, exterior and interior finish
- Foundation (slab, crawlspace or basement)
- Bathroom or kitchen (optional)
- Heating, cooling and electrical panel (optional)
- Architect fees, permits and contingency
What the home addition estimate leaves out
- Landscaping and driveway changes
- Furniture and window treatments
- Unusual site work such as rock or steep slopes
- Utility line relocation beyond the listed items
Home addition cost FAQs
How much does a home addition cost?
Roughly $165 to $550 per square foot, all-in, depending on type: about $235–$485 for a ground-floor room, $270–$550 for a second story and $165–$375 for a sunroom. A 300 sq ft ground-floor room often lands around $73,000–$155,000.
Is a second story cheaper than a ground-floor addition?
It needs no new foundation, so it can save money there, but structural work and the roof rebuild usually make it cost more per square foot overall.
Does the estimate include architect fees?
Yes, unless you turn them off in the last step. Architect and engineering fees usually run $3,000 to $10,000 for a typical addition.
Do I need a permit for a home addition?
Almost always. Permits, plan review and inspections vary widely by city, which is why the permit line is a ballpark.
Why is the contingency higher for additions?
Additions tie into existing structure, electrical and plumbing, which hides surprises. We use a 10-20% buffer instead of the smaller buffer used for simpler projects.
Related guides
- Second Story Addition Cost in 2026Building up avoids a new foundation and keeps your yard, but it means structural work and living through construction.
- Sunroom Addition Cost in 2026A sunroom adds bright living space without the expense of a full room addition.
- Bedroom Addition Cost in 2026A bedroom addition is priced like any room addition: size, foundation and finish level matter most.
- 10 Hidden Costs of Home Renovation (2026)These surprise costs have blown up thousands of renovation budgets.