Start with the right document
Use the exact model’s EnergyGuide label and the relevant cycle information. Annual energy figures, gallons per cycle and a manufacturer’s percentage-saving claim are different quantities. Do not put an annual kWh figure into a calculator field asking for kWh per cycle.
The FTC explains that the label’s cost estimate uses standard assumptions. It helps compare similar appliances; your bill depends on your rates and use.
The routine matters too
A smaller machine is not necessarily more economical for a large household if it takes several loads to wash the same dishes. Compare your likely number of cycles rather than only capacity or consumption for one cycle.
ENERGY STAR recommends scraping food rather than rinsing dishes clean before loading. Follow dishware and appliance guidance, and avoid loading so tightly that items need to be washed again. A full useful load is different from an overloaded rack.
Understand what is left out
A simple electricity-and-water estimate may omit energy used by a separate water heater, detergent, sewer billing differences and fixed charges. A utility bill can also use different units or rate bands. Check the bill before copying a rate into the calculator.
A delay feature can help coordinate a cycle with a tariff, but it does not itself prove lower consumption. Compare the applicable rates and follow household and appliance safety guidance.
Make the numbers useful
Record cycle frequency for a typical week, choose documented consumption figures and enter your actual rates. Treat the result as a planning estimate. If two models differ only modestly in running cost, fit and usability may make the clearer purchasing difference.