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A return on investment (ROI) calculator measures how much financial return an investment generates relative to its cost. ROI is expressed as a percentage and answers the fundamental question: is this worth doing? It is used to compare investments, evaluate projects, assess marketing spend, and make purchase decisions. A positive ROI means the investment returns more than it costs; a negative ROI means it loses money. Loan Payment Calculator and Mortgage Calculator provide related financial tools.

Enter the total cost of the investment (purchase price, installation, setup costs).
Enter the total return or gain (savings, revenue, resale value, benefits).
ROI % = (Return − Cost) ÷ Cost × 100
For time-based ROI, also enter the period to calculate annualised return.
Compare against alternative uses of the same money (savings rate, other investments).

ROI formula

ROI (%) = (Net return ÷ Cost) × 100

Net return = Total return − Total cost

Payback period = Cost ÷ Annual return

Example — Double glazing: Installation cost 5,000. Annual energy saving 350/yr. ROI = (350 ÷ 5,000) × 100 = 7% per year. Payback = 5,000 ÷ 350 = 14.3 years.

Interpreting your ROI result

ROI benchmarks

ROI context: savings account (2–5%/yr); stock market long-run average (7–10%/yr); home improvement ROI varies widely — loft insulation typically 10–15%/yr; double glazing 5–8%/yr; solar panels 6–12%/yr; kitchen renovation 0–5%/yr. Any ROI above your borrowing cost is profitable if funded by debt. Compare against your personal hurdle rate — the minimum return you require to justify the investment risk.

Finance tips and best practices

Include ALL costs — installation, maintenance, disruption — not just the purchase price.
Use realistic, conservative return estimates rather than best-case figures.
Account for the time value of money for long payback periods — a return in 15 years is worth less than the same return in 3 years.
Compare against leaving the money in savings — if your savings rate is 4% and the investment returns 3%, it is not worth doing.

The average home improvement ROI varies from approximately 3% (conservatory) to 15%+ (loft conversion adding usable space).
Solar panel ROI has improved significantly — systems installed in 2024 typically pay back in 7–12 years vs 15–20 years for systems installed in 2012.
LED lighting has one of the highest ROIs of any home improvement — typical payback under 2 years with 10–15+ year lifespan.

Common mistakes to avoid

Ignoring ongoing maintenance costs — boilers, solar inverters, and appliances all have maintenance costs that reduce net ROI.
Not comparing against alternatives — ROI in isolation is less useful than ROI vs other options for the same money.
Overestimating savings — energy savings are often lower than projected due to behaviour changes or installation quality.

ROI calculations are estimates based on current rates and costs which are subject to change. Energy savings depend on usage patterns, tariff rates, and property characteristics. Government schemes may subsidise certain improvements — check current eligibility. This calculator is for planning purposes only and does not constitute financial advice.