Heat is the cost, motion is not
Turning a drum takes very little power. Heating something takes a great deal. That single fact explains the whole shape of the result: a cold wash on a modern machine consumes a few tenths of a kilowatt-hour, while a vented electric dryer working through the same load consumes several times that, because it is heating air and throwing it away for the best part of an hour.
The same logic applies inside the washer. A hot wash costs far more than a cold one, not because the motor works harder but because the machine or the water heater has to raise the temperature of many gallons. Detergents formulated for cold water have made hot washing largely unnecessary for ordinary soil, and switching the default cycle to cold is the change with the best ratio of effort to saving anywhere in this calculation.
Getting the wattage figures right
Nameplate wattage is close to a peak rather than an average. A washer spends much of its cycle filling, soaking and tumbling at low power, then draws hard for a few minutes on the spin. Multiplying the nameplate by the full cycle length overstates it, often by a factor of two or more.
Two better routes. The energy label or the manual usually gives kilowatt-hours per cycle, which is the number you actually want; to enter it here, multiply by 1,000 and divide by the cycle length in hours, so 0.4 kWh over 50 minutes is 400 divided by 0.833, about 480 W. Or put a plug-in energy meter on the machine and read a real cycle, which is the only method that accounts for your water temperature and your loads. A 240 V dryer cannot be metered that way, so its label figure is what you have.
Detergent is priced per fluid ounce, not per bottle
What a bottle costs tells you nothing until you divide by how many loads it does. A hundred-ounce bottle at a dose of one and a half ounces is sixty-six loads; at three ounces, thirty-three. The cap is the usual culprit, since it is far larger than a normal dose and filling it to the brim roughly doubles consumption.
More detergent does not clean better past a point. Once the concentration is sufficient, extra surfactant stays in the fabric rather than lifting soil, and rinsing it out means longer or extra rinse cycles, which cost water and time. In a high-efficiency machine, excess detergent also produces suds the machine then has to work to clear. Dose to the marked line, and dose up only for genuinely dirty loads or hard water.
Comparing home against a laundromat fairly
Running costs alone make home look overwhelmingly cheaper, and that comparison is rigged. A laundromat price covers the machines, the premises, the water heating, the maintenance and the staff. To put the two side by side you have to add something for your own machines, which is why this page takes the purchase price and spreads it over the years you expect them to last.
Even with that added, frequent users come out ahead at home. Where it tightens is at low volume: a single person running one load a week is spreading the price of a washer and dryer across only a few dozen loads a year, and the depreciation share alone can rival a laundromat price. That is the arithmetic behind the common arrangement of using in-unit machines for everyday loads and a laundromat for comforters and bedding that do not fit the drum.
What fuller loads really save, and where the limit is
Fewer cycles means fewer of every fixed cost a cycle carries: filling, heating, running the motor, the detergent floor. So consolidating half-empty loads does save money. The figure on this page is deliberately an upper bound, because it removes cycles while holding the per-load cost constant, and in reality a fuller drum uses a bit more water and takes longer to dry.
The ceiling is mechanical rather than financial. Clothes clean by moving through water and detergent, and a drum packed to the top does not let them move. Manufacturers generally point at about three quarters full, which is where this calculator sets its target, and bulky items that soak up water are heavier wet than a dry-weight estimate suggests. The saving from going from half full to three quarters full is real; the saving from cramming is a laundry problem dressed up as an economy.
Questions people ask
How much does it cost to run a load of laundry?
It is dominated by whether you use a dryer and what you pay per kilowatt-hour, so the honest answer comes from your own numbers rather than a quoted figure. The structure is consistent though: a cold wash on a modern machine uses a few tenths of a kilowatt-hour, a vented electric dryer several times that for the same load, water and sewer add a small amount, and detergent is a matter of cents per fluid ounce multiplied by the dose. Put your rate in and the split appears; in most households the dryer is the majority of the total and the washer is a small minority of it.
Does washing in cold water actually save much?
Yes, and it is the largest single saving available on the wash side, because heating water is where a washer spends its energy. On a machine that heats internally, a hot cycle can consume several times what a cold one does; where the hot supply comes from a household water heater the cost moves to that appliance instead but does not disappear. Detergents sold today are formulated to work at low temperatures, so for ordinary soil the cleaning result is generally indistinguishable. The cases that still warrant hot water are sanitising after illness, heavy grease, and some stains that set at low temperature.
Is a heat pump dryer worth the extra money?
It depends almost entirely on how many loads you run. A heat pump dryer recycles heat instead of exhausting it, so it uses a fraction of the electricity of a vented electric machine, but it costs more to buy and takes noticeably longer per load. Work out the per-load electricity difference on this page by running it twice with the two wattages, multiply by loads a year, and compare that against the price gap. A household doing five or more loads a week recovers it far faster than one doing a couple, and the longer cycle time is a real inconvenience worth weighing separately from the money.
How do I find my water rate for this?
Take the water bill total, including the sewer charge and any fixed charges, and divide by the volume on it, then convert to gallons. Most utilities bill in CCF, which is a hundred cubic feet or 748 gallons, so a bill of ninety dollars for eight CCF is ninety divided by 5,984 gallons, about $15 per thousand gallons. Using the water rate alone understates it badly, because sewer is usually charged on the same metered volume and is often the larger of the two. The water bill calculator on this site does the conversion if you would rather not.
Is line drying free?
Outdoors, effectively yes, and this page shows the full dryer electricity as the saving. Indoors it is cheaper rather than free. A load of wet laundry carries a substantial amount of water that has to evaporate into the house, and in a cold or humid season that shows up as a dehumidifier running, a window open while the heating is on, or condensation on the windows. In a dry climate or a well-ventilated space the cost is genuinely close to nothing. The mixed approach — outdoors when the weather allows, machine when it does not — lands between the two figures shown.