Home Addition Cost Estimator
Pick your size, stories, and room type — get an OC price band.
Orange County, CA · Updated 2026 · Ranges from our cost guides — your quote will vary by contractor and scope
How this calculator works: it combines the cost bands published in our Orange County cost guides with a few choices about your project. The output is a range — low, typical, high — with the assumptions listed. It is a planning tool, not a contractor bid.
Your project
OC bands grounded 2026-10-15 (greatbuildz, ocbuildersgroup).
What drives the cost
- Size and stories — single-story additions run $250–$400/sq ft in OC; going up (second story) runs $400–$600/sq ft because of structural work, stairs, and roof tie-in.
- Dry vs. wet rooms — bedrooms and living space price at the base band; kitchens and baths add ~15% for plumbing, electrical, and venting.
- Soft costs — permits, architectural plans, and engineering commonly add 5–10% beyond the construction band.
- What's in the quote — foundation type, finish level, permit handling, and a payment schedule tied to milestones — never a lump sum up front.
Estimate, not a quote
These numbers are estimates only — not a quote, not a bid. Bands are computed from the cost ranges published in our Orange County cost guides (2026), which are themselves compiled from contractor-published pricing and industry data. Your actual price depends on scope, materials, access, timing, and the contractor. Always get 2–3 written quotes and compare the scope line by line, not just the total. We don't sell services and we have no contractor relationships.