CostRunningThe Cheapest Time to Run Appliances
The honest answer comes in two halves, and which half applies to you depends entirely on your tariff.
On a flat tariff: it makes no difference
If your bill has one unit rate, a kilowatt-hour costs the same at 3 am and 6 pm. Running the dishwasher overnight saves nothing at all. The widely repeated advice to use appliances at night is inherited from countries and decades where nearly everybody was on a two-rate meter.
There is one small exception: appliances that make heat are marginally cheaper to run in a cool house in summer, because the air conditioning does not then have to remove that heat. It is a real effect and a small one.
On a time-of-use tariff: it makes a large difference
If your bill has more than one rate, moving load out of the evening peak is the biggest saving available to most households — bigger than replacing any single appliance.
Typical shapes:
| Tariff type | Cheap window | Typical saving on shifted load |
|---|---|---|
| Economy 7 (UK) | roughly 00:30–07:30 | 50–60% |
| US off-peak | usually 21:00–07:00 | 30–60% |
| EV tariff | a 4–6 hour overnight block | 60–75% |
| Australian off-peak | 22:00–07:00 | 40–60% |
What is worth shifting
Worth it: dishwasher, washing machine, tumble dryer, EV charging, water heater on a timer, pool pump. All are hours-long, unattended, and easy to delay.
Not worth it: kettle, oven, hob, television, lighting. All are short, attended, or not optional at that hour — and nobody is going to cook dinner at 1 am to save four cents.
Depends: hot tub and dehumidifier, both of which run on thermostats rather than timers. Some controllers let you restrict heating to a window; most do not.
The safety note nobody mentions
Running a tumble dryer or a dishwasher unattended overnight is a real fire-risk trade-off, and the appliance manufacturers say so in the manual. Both are among the more common causes of household fires. If you shift them, shift them to a time when somebody is awake — early morning rather than the middle of the night.
Solar changes the question entirely
With solar panels the cheapest electricity is not overnight but in the middle of the day, when your own generation would otherwise be exported for a fraction of what you pay to import. On a sunny day the dishwasher at noon is close to free; at midnight it is full price.
Whatever your tariff, the number to put into the electricity cost calculator is the one that applies while the appliance actually runs — which on a multi-rate tariff means running the calculation twice and comparing.