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Home Addition Project Budget Planner

This budget planner combines the major cost buckets of a home addition into one project total and applies a contingency reserve to the pre-contingency budget. It is designed for early planning when you have rough quotes or allowances for materials, labor, professional services, permits, and utility or site work but need a consistent way to see the full capital requirement.

The calculator shows both the base budget and the contingency amount so you can identify how much of the total is committed scope versus risk reserve. It also reports cost per square foot when an addition area is provided. A planning budget is not a contractor bid: financing charges, temporary housing, furniture, taxes, escalation, owner upgrades, and project-specific code work may need separate lines. Replace placeholder estimates with current local quotes as the design becomes more defined.

Addition budget inputs

sq ft
USD
USD
USD
USD
%
Result
—
planned project budget
Base budget—
Contingency reserve—
Budget per sq ft—

1. Set the project area
Enter the approximate finished square footage of the addition for a comparable cost-per-square-foot figure.

2. Enter direct construction costs
Add current material and labor estimates from your scope, quantity takeoff, or contractor discussions.

3. Add soft and enabling costs
Include design, permitting, site preparation, utility connections, and similar non-finish expenses in the matching fields.

4. Choose a contingency
Set a reserve percentage for uncertainty in scope, pricing, and field conditions.

5. Review the total and unit cost
Use the full budget for funding needs and the per-square-foot result to compare options with the same scope definition.

Base budget = Materials + Labor + Design and permits + Site and utility work

Contingency reserve = Base budget × (Contingency % ÷ 100)

Planned project budget = Base budget + Contingency reserve

Budget per square foot = Planned project budget ÷ Addition area

The contingency is calculated on the entered base cost. Items not represented by the four cost buckets must be added to the most appropriate field or tracked separately.

What the result means

Use the main result as a planning estimate based on the values entered. Compare it with project-specific quotes, drawings, measurements, or operating assumptions before making commitments.

Actual results can differ when scope, site conditions, material specifications, labor productivity, prices, or local requirements differ from the assumptions entered.

Given
• Area = 600 sq ft
• Materials = $65,000
• Labor = $85,000
• Design and permits = $18,000
• Site and utility work = $22,000
• Contingency = 12%

Calculation
Base budget = 65,000 + 85,000 + 18,000 + 22,000 = $190,000
Contingency = $190,000 × 0.12 = $22,800
Total budget = $190,000 + $22,800 = $212,800
Budget per sq ft = $212,800 ÷ 600 = $354.67

Result
Planned project budget: $212,800, or about $354.67 per sq ft.

The contingency is a reserve within the plan, not an assumption that it will necessarily be spent.

Should contractor overhead and profit go in labor?

If a contractor quote already includes overhead and profit, enter the quoted amount in the most appropriate construction field without stripping those components out. The key is to avoid double-counting.

What should the contingency percentage cover?

Use it for uncertainty such as incomplete design details, minor scope changes, and field conditions. Major known items should be budgeted explicitly rather than hidden inside contingency.

Does cost per square foot make two additions directly comparable?

Only when the scope and quality level are similar. Kitchens, bathrooms, structural complexity, utility relocation, and high-end finishes can make equal-size additions very different in cost.

Are financing costs included?

No. Loan origination fees, interest, carrying costs, and similar financing expenses are not separate inputs in this planner.

When should I update the budget?

Revise it whenever drawings, quantities, bids, or permit requirements become more specific. Early allowances should progressively be replaced with current committed or quoted costs.