How to Use This Calculator

This tool covers three common home improvement projects in one calculator — switch between the Roofing, Windows, and Solar tabs depending on what you're evaluating. Each tab has its own inputs and its own output metrics, since the economics of each project are different.

Roofing estimates replacement cost against the home equity a new roof typically adds. Windows estimates annual HVAC energy savings from upgrading to energy-efficient units. Solar estimates 20-year electricity bill savings alongside the federal solar tax credit value.

What the Inputs Mean

  • Sq Footage (Roofing): The footprint of your roof in square feet — not your home's total living area.
  • Roof Age (Roofing): How old your current roof is, for context on replacement urgency; it does not change the cost estimate itself.
  • Window Count (Windows): The number of windows you're considering replacing with energy-efficient units.
  • Monthly Power Bill (Solar): Your typical monthly electricity bill, used to size a representative solar system and estimate offset savings.

Assumptions & Formula

  • Roofing uses an estimated $8.50 per square foot (mid-range asphalt shingle, materials and labor combined) and assumes a replaced roof recoups roughly 60% of its cost as added home equity — both figures are national averages and vary significantly by region, roofing material, and local labor costs.
  • Windows assumes roughly $40 per window in annual HVAC savings from upgrading older single-pane windows to modern energy-efficient units — actual savings depend on your climate, current windows, and home insulation.
  • Solar assumes the system offsets about 90% of your electricity usage, estimates a representative system cost at roughly 5x your annual power bill, and applies the 30% federal residential solar tax credit to that estimated cost. It does not account for net metering policy, panel degradation, or state/utility incentives, which can meaningfully change your real payback period.
  • All three estimates are for illustrative, planning purposes only — always get multiple local contractor quotes before committing to a project.

Formula: Roofing: Cost = Sq Footage × $8.50; Equity Added = Cost × 60%. Windows: Annual Savings = Window Count × $40. Solar: 20-Year Savings = Monthly Bill × 12 × 20 × 90%; System Cost Estimate = Monthly Bill × 12 × 5; Tax Credit Value = System Cost Estimate × 30%.

Worked Example

Roofing: a 2,000 sq ft roof at $8.50/sqft estimates to $17,000 in cost, with about $10,200 in added equity — a net investment of roughly $6,800. Windows: replacing 12 windows estimates to about $480/year in HVAC savings. Solar: a $180/month power bill estimates to roughly $38,880 in savings over 20 years, against an estimated system cost of $10,800 and a federal tax credit worth about $3,240.

Frequently Asked Questions

Are these real contractor quotes?

No — these are rough, national-average estimates meant to help you plan and budget. Actual costs vary by region, materials, contractor, and the condition of your home. Always get multiple local quotes before committing.

Does the roofing estimate account for roof pitch, layers to remove, or material type?

No — it uses a single blended average cost per square foot across common asphalt-shingle jobs. Steep pitches, multiple tear-off layers, or premium materials (metal, tile, slate) will cost more than this baseline estimate.

Is the federal solar tax credit guaranteed?

The 30% federal residential solar tax credit has historically been subject to phase-downs and legislative changes, so confirm the current rate and eligibility rules before relying on this estimate for tax planning.

Why does the window estimate use a flat dollar amount instead of a percentage?

Window energy savings depend heavily on what you're replacing and your local climate, so a flat per-window average is a simpler, more conservative estimate than trying to model your specific HVAC system.

Sources

  • Methodology note — Cost-per-square-foot, equity-recoup, HVAC savings, and solar offset figures are blended national averages for illustrative estimates, not pulled from a live data feed.