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HOME ADDITIONS

Home Addition Cost Calculator

Estimate the cost of a home addition by square footage, floors, foundation, finish level and contingency.

JOB INPUTS

Enter your numbers

Loading saved values

Addition footprint in sq ft

sq ft
Addition footprint in sq ft

How many stories the addition has

How many stories the addition has

Foundation type

Foundation type

Quality of finishes

Quality of finishes

Structural framing type

Structural framing type

Mechanical and electrical work

Mechanical and electrical work

Architect and design fees

Architect and design fees

Include permit fees

Include permit fees

Percentage reserve

%
Percentage reserve
Results update automatically
CALCULATED RESULTUSD
Estimated total cost$114,180.00
Foundation$3,600.00
Structure$4,500.00
MEP$12,600.00
Finish work$76,500.00
Design + permits$6,600.00
Contingency (10%)$10,380.00
FORMULA USED450 sq ft × $170.00 + components + contingency = $114,180.00

HOW TO USE IT

How to use the Home Addition Cost Calculator

  1. 1

    Enter the addition footprint in sq ft.

  2. 2

    Choose the number of stories and foundation type.

  3. 3

    Select finish level and structure/MEP complexity.

  4. 4

    Set design, permits and the contingency percentage.

THE MATH

Home addition cost formula

Total = (foundation + structure + MEP + finishes + design + permits) + contingency

The finish base rate runs $120/sq ft (budget) to $220/sq ft (premium). Foundation, structure and MEP add per sq ft. Recommended contingency is 10-15%.

PRACTICAL EXAMPLE

450 sq ft addition, 1 story, slab, standard finish

Foundation = $3,600. Structure = $4,500. MEP = $12,600. Finishes = $76,500. Design + permits = $6,600. Contingency 10% = $10,380. Total = $114,180.

FAQ

Frequently asked questions

How much does a home addition cost in 2026?

With the displayed standard assumptions, the 450 sq ft example is $114,180. Replace every allowance with local design, trade and permit quotes.

Do I need an architect?

Drawing and stamp requirements vary by jurisdiction and scope; confirm them with the local building department before bidding.

What contingency should I budget?

10-15% is a planning allowance; additions on older homes may need more after investigation.