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Home Addition Cost Calculator

Build-out vs build-up, priced honestly — the per-square-foot number that drives 80% of your budget.

Quick answer

Home additions cost $80–$200 per square foot for ground-level build-outs and $300–$500 per square foot for second-story additions in 2026, averaging about $51,000 total. A 400 sq ft room addition runs roughly $48,000–$100,000; the same space as a second story costs $120,000–$200,000.

Calculator

sq ft

How it works

Sq ft × type rate × finish multiplier

Type rates (2026): bump-out $80–$200, room addition $120–$250, sunroom $110–$190, garage $150–$300, second story $300–$500 per sq ft. Basic finishes 0.85x, luxury 1.35x. Add ~10–15% for architectural plans and permits.

Up vs out is the 3x lever

Second stories need structural reinforcement, temporary roofing, and stairs — nearly triple the per-square-foot cost of ground-floor space.

Worked example

400 sq ft room addition, mid-range:

400 × $185 = $74,000

+ design/permits ~12% = $8,880

All-in ≈ $82,880

Range: $48,000 – $100,000 construction.

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A home addition is the biggest check most homeowners will ever write to a contractor — and the quotes swing wildly because "per square foot" means different things to different builders. One bid includes the foundation and roof tie-in; the next treats them as extras.

This calculator uses 2026 per-square-foot rates by addition type — bump-out to second story — with finish-level adjustments, so you walk into bid meetings with a number the contractor has to argue against, not invent.

How to scope your addition before pricing

  1. Define the room's purpose: wet rooms (bath, kitchen) cost nearly double dry rooms per square foot.
  2. Choose up vs out: ground-floor is $80–$200/sq ft; second story is $300–$500/sq ft.
  3. Measure the footprint honestly — additions under 100 sq ft have worse $/sq ft economics (fixed costs spread thin).
  4. Budget 10–15% on top for architectural plans and permits before construction starts.

Home addition cost (2026 US averages, $/sq ft)

Addition type$/sq ftTypical total
Bump-out (60–100 sq ft)$80–$200$4,800–$20,000
Room addition$120–$250$30,000–$100,000
Sunroom / 3-season$110–$190$20,000–$60,000
Attached garage$150–$300$35,000–$100,000
Second story$300–$500$120,000–$250,000
Design + permits adder—+10–15% of build

2026 ranges. Sources: angi.com, Bankrate, yardandgardenguru.com.

Worked example: 400 sq ft room addition, mid-range

400 sq ft ground-floor family room addition, mid-range finishes:

  1. Base: 400 × $185 (mid room-addition rate) = $74,000.
  2. Finish: mid-range = 1.0x multiplier.
  3. Range: 400 × $120 = $48,000 low; 400 × $250 = $100,000 high.
  4. Soft costs: +~12% design/permits ≈ $8,900.

~$74,000 construction + ~$8,900 soft costs ≈ $83,000 all-in for a 400 sq ft mid-range addition.

Pro tips for home additions

  • Get the tie-in scope in writing: roof, siding, flooring transitions, and HVAC extension are the classic "extras."
  • Build during the shoulder season — framers discount 5–10% in late fall vs peak summer.
  • A structural engineer ($500–$2,000) before design saves 10x in change orders on second stories.
  • Check setback and lot-coverage rules FIRST — zoning kills more additions than budgets do.
  • Finance with a HELOC or construction loan, not credit cards: rates and draw schedules matter at this scale.

How to use the home addition cost calculator

Enter the addition's square footage, pick the addition type (bump-out, room, second story, sunroom, or garage), and choose a finish level. The calculator applies 2026 per-square-foot rates — the single number that determines 80% of your budget.

How home addition cost is calculated

Total = sq ft × type rate × finish multiplier. Type rates (2026): bump-out $80–$200, room addition $120–$250, sunroom $110–$190, garage $150–$300, second story $300–$500 per sq ft. Basic finishes multiply by 0.85x, luxury by 1.35x. Design fees, permits (~10–15%), and site work sit on top.

What drives home addition cost the most?

Up vs out is the 3x lever — second stories cost nearly triple ground-floor space. Then: wet vs dry rooms (plumbing adds $150–$200/sq ft), foundation conditions, and roofline complexity. The quote-trap: tie-in work (matching siding, roofing, and flooring) is often underestimated in per-square-foot quotes.

Home addition cost example

400 sq ft room addition, mid-range finishes: 400 × $185 = ~$74,000, ranging $48,000–$100,000. Same 400 sq ft as a second story: 400 × $400 = ~$160,000, ranging $120,000–$200,000. Add ~10–15% for design and permits on top.

Addition vs ADU vs finishing the basement

Before committing: a finished basement runs $40–$80/sq ft (cheapest new living space), a detached ADU $200–$400/sq ft but adds rental income potential, and a ground-floor addition $120–$250/sq ft. If you just need a bedroom or office, the basement usually wins on cost per square foot.

Frequently Asked Questions

How much does a home addition cost in 2026?+
Home additions cost $80–$200 per square foot for ground-level build-outs and $300–$500 per square foot for second-story additions in 2026. The national average is about $51,000, with most projects landing between $22,000 and $83,000.
What is the cheapest type of home addition?+
Bump-outs (2–3 ft extensions of an existing room) are cheapest at $80–$200 per square foot — a 60 sq ft bump-out runs $4,800–$12,000. Sunrooms are next at $110–$190/sq ft. Second stories are the priciest at $300–$500/sq ft due to structural reinforcement.
Is it cheaper to build out or build up?+
Building out (ground level) is far cheaper: $80–$200 per square foot vs $300–$500 for building up (second story). Going up requires structural reinforcement of the existing frame, temporary roofing, and stair installation — typically 20–35% more per square foot for the same space.
How much does a 400 sq ft addition cost?+
A 400 sq ft ground-floor addition costs roughly $32,000–$80,000 at $80–$200 per square foot (mid-range ~$56,000–$72,000). The same 400 sq ft as a second story runs $120,000–$200,000. Kitchens and bathrooms push higher; bedrooms and living rooms land lower.
What is the ROI on a home addition?+
Additions recoup roughly 35–70% at resale depending on type — mid-range additions land near 60–70%, major two-story additions closer to 35–42% (Remodeling Magazine Cost vs. Value). You're buying years of use, not a resale windfall — budget accordingly.
Do I need a permit for a home addition?+
Yes — virtually all additions need building permits, and many need zoning review for setbacks and lot coverage. Permit and design fees run about 10–15% of the project budget. Skipping permits risks stop-work orders, insurance denial, and resale disclosure problems.

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