How the figure is calculated
Dryers are rated by the energy they use over a standard year of loads, so we start there. US models come from the ENERGY STAR list, whose annual kWh assumes 283 cycles (10 CFR 430, Appendix D2). EU-label models sold in Britain declare a weighted annual figure based on 160 drying cycles of full and partial loads (Regulation 392/2012). Annual kWh divided by those cycles gives kWh per load, a derived figure we label as such; multiplied by your price per kWh it gives the cost per load.
Loads per week start at the official rate and can be changed.
What drives the cost
Technology first. Heat-pump dryers recycle warm air and use a fraction of the energy of vented or condenser models: the LG DLHC1455 heat-pump dryer lists 133 kWh a year against 607 kWh for the vented LG DLE7150. After that come load size, how wet the clothes are when they go in, and how many loads you run.
Worked example
US: the LG DLE7150 vented dryer at 607 kWh over 283 cycles is 2.14 kWh a load, or 39.27¢ at 18.31¢/kWh, and $111.14 a year at the DOE rate. The heat-pump LG DLHC1455 comes to 8.61¢ a load and $24.35 a year.
GB: the Bosch WQH246B0ES heat-pump condenser dryer declares 171 kWh over 160 cycles, 1.07 kWh a load. At 26.32p/kWh that is 28.13p a load and £45.01 a year. Its full-load cotton cycle was measured higher, at 1.44 kWh, so big wet loads cost more than the average.
Cheaper drying
Spin at the highest speed your washer allows, dry full loads, and clean the lint filter every time. If you dry most days, the heat-pump figures above show why the upgrade can pay back.
Questions
Why is a US vented dryer so much more expensive per load than the British example?
The British example is a heat-pump model; vented dryers in the US list use more than four times the energy of the heat-pump one.
What if I run fewer loads than the standard?
Change loads per week. The cost per load stays the same; weekly, monthly and yearly totals follow your number.
Is a gas dryer covered?
No. Only electric dryers are listed here.