Home Addition Cost Calculator
Get a realistic 2026 price range for your home addition in seconds. Pick a size and quality level — no email required.
Size / scope
Quality level
A home addition is essentially building a small house onto your existing one — foundation, framing, roof, siding, and full interior — so it's one of the priciest projects a homeowner takes on. Cost depends on square footage, whether it's a bump-out or a full room, and how much finished space (like a bathroom) it includes. This calculator estimates a room-sized addition.
What drives home addition cost
- Square footage and foundation — new footings, slab, or crawlspace scale directly with size
- Tying into the existing structure — matching the roofline, siding, and connecting HVAC and electrical
- Whether the addition includes plumbing (a bathroom or kitchen dramatically raises cost)
- Permits, structural engineering, and possible zoning or setback requirements
Home Addition cost — frequently asked questions
Is it cheaper to add on or build up?
Building out (on-grade) usually costs less per square foot than building up (a second story) because a second story often requires reinforcing the existing foundation and framing and temporarily removing the roof. Site constraints and lot size ultimately decide which is feasible.
How much does it cost to add a room?
A basic room addition without plumbing sits in the lower-to-middle part of this range; adding a bathroom, kitchen, or high-end finishes pushes it up. Set size and quality to match the scope of your addition.
Do I need a permit and inspections for an addition?
Always. Additions require building permits, structural review, and multiple inspections (foundation, framing, electrical, plumbing). Many areas also have setback and zoning rules. Those costs are captured in the 'Permits, design & cleanup' line.