The short answer
Match capacity, task, programme and energy boundary before comparing costs. Use annual kWh directly; divide per-100-cycle energy by 100 before multiplying by weekly cycles and 52 weeks. Multiply compatible annual quantities by the same tariff. Converting units does not make different tests equivalent.
Match the task before the arithmetic
Compare options that meet the same household need. Check capacity, programme basis, source regime and any related energy included in the figure.
The FTC’s EnergyGuide guidance and the Commission’s EPREL guidance help you identify product information. A compatible unit is necessary, but it does not by itself establish a compatible test.
Normalize the stated energy units
The comparison calculator can use annual kWh directly or annualize cycle figures using your shared weekly frequency and 52 weeks.
Consider illustrative, compatible cycle figures:
| Candidate | Source quantity | At four cycles/week |
|---|---|---|
| A | 60 kWh / 100 cycles | 124.8 kWh/year |
| B | 0.45 kWh / cycle | 93.6 kWh/year |
At €0.30/kWh, annual running costs are €37.44 and €28.08. B saves €9.36/year.
The different units are harmless after the correct conversion. A different programme or source scope would remain a problem after conversion.
Add the purchase-price difference
If A costs €500 and B €620, B costs €120 more. Simple extra-price payback is €120 ÷ €9.36 = about 12.8 years.
Across five years, the modeled purchase-plus-electricity totals are €687.20 for A and €760.40 for B. B has lower running cost but costs €73.20 more over that period.
This comparison holds price and consumption constant. It does not predict a 12.8-year service life, nor account for repairs, finance or disposal.
Set a purchase-price ceiling from electricity savings
The comparison calculator now shows the maximum extra purchase price that B’s electricity savings cover over your chosen period. In the cycle example above, €9.36/year × five years = €46.80. An extra €120 is above that electricity-only ceiling at the entered tariff; other benefits would need their own justification.
It also shows the break-even electricity rate. Here, €120 ÷ 31.2 kWh/year ÷ five years = about €0.769231/kWh. At that rate the purchase-plus-electricity totals match; higher tariffs favor the more efficient B. Keep the full-precision calculation separate from its rounded display.
If B is cheaper upfront but uses more annual electricity, the direction reverses: tariffs below its positive crossover favor B. Equal consumption or an option that costs more upfront and uses more electricity has no useful non-negative tariff crossover. These thresholds use the chosen period and constant consumption; they are not forecasts of appliance life or live product prices.
Handle different annual bases carefully
An annual label quantity cannot be personalized to your cycle count by guessing its underlying test frequency. If one candidate has only annual energy and another has cycle energy, check whether their source bases support the intended comparison.
The calculator will normalize the inputs you select, but it does not certify that the source conditions are equivalent.
Use the right decision baseline
This tool compares two purchase options. If you already own a working appliance, replacement payback compares a net replacement outlay with keeping it.
Open the appliance comparison calculator, read the total-cost guide, or check an energy-label model record.