How the figure is calculated
Fridges are tested over a standard year, compressor cycling included. US models carry the annual kWh from the ENERGY STAR list (DOE test, 365 days of average use); British models carry the kWh per annum from the EU energy label. We multiply that by your price per kWh for the year and divide by 365 for a day. No hours box, no duty cycle: the test already covers both.
If you have your own fridge, type the kWh/year printed on its label.
What drives the cost
Size and features: an ice maker added 84 kWh a year to the same Frigidaire FFHT1814W in the ENERGY STAR list, and a 27.8 cu ft French-door GE uses about twice the energy of an 18 cu ft top-freezer. The efficiency class matters as much in Europe: two 366-litre Bosch fridge-freezers are labelled 182 and 273 kWh. A warm kitchen and a door left open push real use above the label.
Worked example
US: the Frigidaire FFHT1814W top-freezer is listed at 369 kWh a year. At 18.31¢/kWh that is $67.56 a year, 18.51¢ a day and $5.55 a month. The ice-maker version at 453 kWh is $82.94 a year.
GB: the Bosch KGN39VLEA fridge-freezer is labelled 273 kWh a year, which at 26.32p/kWh is £71.85 a year, about 19.69p a day. The A+++ KGN39MIDP of the same size, at 182 kWh, costs £47.90.
Keeping it cheap
Leave space behind the fridge for air, keep the seals clean, and set it to the recommended temperature. An old second fridge in the garage is often the most expensive appliance nobody looks at.
Questions
Should I switch a fridge off at night?
No. It would warm up and then work harder to cool down again, and food safety suffers.
Why is the UK cost higher for a smaller fridge?
The British price per kWh is higher than the US average, and the KGN39VLEA is an A++ model; check the A+++ example for the difference efficiency makes.
Is the label figure exactly what my fridge uses?
It is a standard test result. Room temperature and how often the door opens move the real figure up or down.