Home Addition Cost Calculator & Estimator
Estimate a home addition from the published low, typical, and high cost per square foot, then scale the labor share by a state’s construction wage index. Estimate (non-official)
Estimated range at the U.S. median
$43,325.00 – $124,750.00
Typical estimate $87,850.00 ($219.63 per sq ft) Estimate (non-official)
| Hard cost | $40,000.00–$100,000.00 (typical $75,000.00) |
|---|---|
| Foundation adjustment | $0.00–$0.00 (typical $0.00) |
| Systems | $0.00–$0.00 (typical $0.00) |
| Design fees | $3,000.00–$20,000.00 (typical $10,312.50) |
| Permit | $325.00–$4,750.00 (typical $2,537.50) |
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Types of additions
Each rate is the researched range for that project type. Finish level in the calculator selects the low, typical, or high column. Estimate (non-official)
| Type | Low–typical–high per sq ft | Sources |
|---|---|---|
| Bump-out | $82.50–$200.00 (typical $141.25) Estimate (non-official) | |
| Single-room ground-floor addition | $100.00–$250.00 (typical $187.50) Estimate (non-official) | |
| Primary suite (bedroom + bath) | $297.03–$387.20 (typical $342.11) Estimate (non-official) | |
| Sources disagree. Large conflict: CVV national cost per sq ft is about 2-2.5x HomeGuide's. | ||
| Second-story addition | $150.00–$400.00 (typical $275.00) Estimate (non-official) | |
| Sources disagree. | ||
| Attached garage | $36.70–$90.00 (typical $63.35) Estimate (non-official) | |
| Sources disagree. Sources conflict (Angi ~$30 vs HomeGuide ~$43-$150 derived). Fixr $23,000-$45,000 (no size) not used. | ||
| Sunroom | $100.00–$350.00 (typical $225.00) Estimate (non-official) Single published source. | |
| In-law suite / attached ADU | $100.00–$275.00 (typical $187.50) Estimate (non-official) | |
20x20 home addition cost
A 20×20 addition is 400 sq ft. Using a mid-range room, a slab, no extra bathroom or kitchen, the architect fee on, and a construction wage index of 1.00 (the U.S. median), the range is $43,325.00 to $124,750.00, typical $87,850.00 ($219.63 per sq ft). Estimate (non-official) Choose a state in the calculator to replace the index of 1.00 with that state’s OEWS construction wage index.
Second story vs ground floor
A ground-floor room is typically $187.50 per sq ft ($100.00–$250.00). A second story is typically $275.00 per sq ft ($150.00–$400.00). Estimate (non-official) The second-story choice sets foundation work to none, because the new floor area is over the existing house.
Home addition cost per square foot
The type table above is the cost-per-square-foot guide. Bathroom and kitchen square footage inside the addition use their own rates instead of the type rate. The Census figures below are context for new houses, not additions.
| Census region | Median | Average |
|---|---|---|
| Midwest | $194.09 | $202.13 |
| Northeast | $179.30 | $246.26 |
| South | $157.30 | $179.96 |
| West | $176.87 | $213.85 |
Census figure is for new single-family houses, not additions. Relative standard errors are published in the CHARS workbook; this table shows the median and average only.
What affects addition costs in your state
Pick a state in the calculator. The wage table uses the OEWS median hourly wage for that state. The cost formula uses the construction-and-extraction wage index, not these trade rates directly.
| Trade | Median hourly |
|---|---|
| Carpenters | $29.12 |
| Construction laborers | $22.66 |
| Electricians | $30.38 |
| Plumbers | $30.67 |
| HVAC | $29.33 |
Questions
How much does a 20x20 home addition cost?
A 20 by 20 room is 400 sq ft. At the U.S. median construction wage (index 1.00), mid-range finish, slab foundation, no extra bath or kitchen, and the architect fee on, the range is $43,325.00 to $124,750.00 (typical $87,850.00, $219.63 per sq ft). Estimate (non-official). Pick a state to apply that state’s construction wage index.
How does a second-story addition compare with a ground-floor room?
The researched typical rate is $187.50 per sq ft for a ground-floor room and $275.00 per sq ft for a second story (ranges $100.00–$250.00 and $150.00–$400.00). Estimate (non-official). A second story does not add foundation area in this calculator.
Do the addition prices already include a foundation?
The guides are treated as including a basic slab. Choosing crawl, basement, or pier-and-beam adds the difference versus that slab, times local labor adjustment. Choosing none adds no foundation dollars. That slab assumption is editorial; the guides do not state it.
Why does my state change the addition estimate?
Only the labor share is scaled. With a labor share of 50%, the local factor is 1 minus that share plus that share times the state’s construction wage index (BLS OEWS, all construction and extraction occupations, versus the U.S. median).