When to use this calculator
Estimate simple payback time for an efficiency upgrade. Excludes financing, maintenance, tariff changes, discounting and changes in usage.
Explore the electricity use & bills calculators for other questions in this topic. For a related calculation, use the Heat Loss From U Value Calculator: Estimate steady heat transfer through an envelope area using an overall U-value.
PUTTING IT INTO PRACTICE
Energy Payback: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Upfront cost | 500 |
| Annual energy saving (kWh) | 600 |
| Price per kWh | 0.3 |
| Result | 2.777778 years |
- Check the input labels and enter the example values above.
- Apply the relationship: Payback = upfront cost ÷ (annual kWh saved × unit price).
- The result is 2.777778 years, rounded for display.
How to interpret your result
Excludes financing, maintenance, tariff changes, discounting and changes in usage.
Watts describe power and kilowatt-hours describe energy. Fixed charges do not vary directly with consumption. Devices with thermostats or cycling loads need measured average energy or realistic operating time.
Frequently asked questions
Can I multiply rated watts by 24 hours for every appliance?
Only if it actually draws that power continuously. Cycling and variable-power appliances require a better average-use estimate.
How do I use the energy payback calculator?
Enter upfront cost, annual energy saving (kwh), price per kwh. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Payback = upfront cost ÷ (annual kWh saved × unit price).
What should I check before using the result?
Excludes financing, maintenance, tariff changes, discounting and changes in usage.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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