Home Addition Cost Calculator

HomeAdvisor puts typical home additions at $80 to $200 per square foot, with most projects landing between $20,000 and $100,000 depending on size, type, and finishes. As a reference from this calculator, a 200 sq ft mid-range bedroom addition in an average-cost state estimates $36,630.00 all-in (permits, design fee, and 10% contingency included), while a 600 sq ft second-story addition in California estimates $183,150.00. Kitchen and bathroom additions cost far more per square foot because of plumbing, electrical, and fixtures.

Mid-grade shell costs in our model run from $60 per sq ft for an attached garage to $325 per sq ft for a kitchen, with bedrooms at $150 and second-story additions at $200 per sq ft. After regional pricing, permits (~3%), design fees (~8%), and contingency (~10%), a bedroom addition totals about $183.15 per sq ft all-in. Published national ranges: bedrooms $100-$250, bathrooms $180-$400, kitchens $200-$500, bump-outs $85-$300, sunrooms $120-$300, garages $40-$100, and second stories $100-$300 per sq ft.

Second-story additions typically run $100 to $300 per square foot (Forbes), because you avoid a new foundation but pay for structural reinforcement, a new roof line, and stairs. A 600 sq ft mid-range second-story in California estimates $183,150.00 all-in with permits, design, and contingency - about $305.25 per sq ft. You can skip the foundation line item for second-story projects, but keep roofing and HVAC.

Bump-outs - small extensions of an existing room that tie into the current roof - run $85 to $300 per square foot. A 100 sq ft mid-range bump-out in Texas estimates $20,299.13 all-in. They are cheaper per project than full additions because there is no new roof and minimal foundation work, but the $/sqft stays high since mobilization and permits do not shrink with size.

An attached garage is the cheapest per square foot (mid-grade shell $60/sqft; published range $40-$100), because it is unfinished space. A 480 sq ft garage in Mississippi with foundation, roof tie-in, and electrical estimates $52,619.00. For living space, a small bump-out is usually the cheapest project overall - a 100 sq ft bump-out estimates $20,299.13 in Texas. Kitchens and bathrooms are the most expensive per square foot.

A 200 sq ft mid-range bedroom addition in an average-cost state estimates $36,630.00 all-in (permits, design fee, and 10% contingency included), or about $183.15 per sq ft. In Hawaii (1.30x regional multiplier) the same project estimates $47,619.00. Basic finishes multiply the shell by 0.80 and high-end finishes by 1.40, so the finish level alone swings the total by tens of thousands.

Yes - virtually every jurisdiction requires a building permit for an addition, plus plan review and inspections. Our default budgets 3% of construction cost for permits and plan-check (for the bedroom example, that is $900.00), adjustable from 0 to 10%. Permit fees vary widely by city and county; high-cost metros often charge flat fees plus valuation-based surcharges. Skipping permits risks stop-work orders, insurance denial, and resale problems.

Design fees for a residential addition typically run 5 to 15% of construction cost; our default is 8% (for the bedroom example, $2,400.00). Simple bump-outs and garage additions may only need a drafter at the low end, while second-story additions and kitchens usually need a licensed architect or structural engineer, especially where structural reinforcement is involved.

Contractors commonly recommend 10 to 20% contingency for remodels, and older homes deserve the high end. Our default is 10% (for the bedroom example, $3,330.00); the slider goes to 25%. Common surprises: rotted framing where the addition ties in, undersized electrical panels, and soil or drainage issues under new footings.

Historically, additions recoup roughly 45 to 65% of their cost in resale value, depending on type: second-story ~65%, bedroom and bump-out ~62%, kitchen ~60%, bathroom and garage ~55%, sunroom ~45% (Cost-vs-Value-style estimates, not appraisals). For the bedroom example ($36,630.00 cost), the estimated resale value added is $22,710.60. Additions usually beat moving when you love your location, but they rarely pay for themselves outright - build for the space, not the flip.

They are the priciest per square foot because of plumbing, electrical, cabinets, and fixtures. A 120 sq ft bathroom addition in Florida with plumbing and electrical line items estimates $51,684.93 all-in. A 300 sq ft high-end kitchen addition in New York with plumbing, electrical, and HVAC estimates $219,047.40 - about $730.16 per sq ft. If you only need more kitchen space, compare against a kitchen remodel first.

Common options: HELOC, home equity loan, construction loan, or cash-out refinance. Financing the bedroom example ($36,630.00) at 8% APR over 15 years costs about $350.06 per month. Use the financing tab to compare HELOC (variable, interest-only draw period), construction loan (interest-only during build, then converts), and home equity loan (fixed rate and payment). Confirm terms with your lender - rates shown are editable 2024-2026-typical starting points.

An addition expands your existing home; an ADU is a separate dwelling unit that can generate rental income. Additions historically recoup about 62% of cost in appraised value with no income, while an ADU's value tracks its rental income. If your goal is space for your family, build the addition. If your goal is income, model both with our ADU cost lab, which compares ADU vs. addition side by side.