Electricity Cost Calculator

How to use

1. Enter the appliance's power in Power (W), as printed on its label or in its manual. 1,200 and full-width １２００ are read too.
2. Enter Use per day in hours and minutes. A decimal such as 1.5 hours works, and so do minutes alone, such as 10.
3. Change Days used per month (30 to begin with) and Units if you need to.
4. The result shows the cost per month in large type. Below it, a statement sets out on one line the cost in yen per hour, day, month, and year, and the energy in kWh per month and year. The units are in the column headings.

For appliances such as fridges and air conditioners whose catalogs give a yearly energy in kWh/year, switch to By yearly energy and enter that figure. For an appliance worked out from its yearly energy, the hour column shows "—" and the day column shows an average, marked "avg". Add an appliance lists up to 10: the statement then has a line for each appliance and a total line under a rule, and each line shows its share of the monthly total. The strip above the statement is the monthly total cut into a piece per appliance, each as long as its share. A piece and the square beside the appliance's name in the statement have the same color. Copy result copies each appliance's cost and the total as text.

Comparing a replacement

Switch to Compare a replacement at the top to set the running cost of the appliance you use now beside the one you might replace it with.

1. For both Current and Replacement, enter the power and use per day, or the yearly energy. For fridges and air conditioners, the yearly energy in your current appliance's manual and in the catalog of the new one make for an easy comparison.
2. The result shows in large type how much less the replacement costs to run in a year, or how much more when it costs more. The statement has a line for each appliance and a Difference line under a rule. The difference is the replacement less the current appliance, so a saving has a "−" and an extra cost a "+".
3. Enter the price and any installation charge in Cost of the replacement (yen, optional) to see after how many years and months of use the savings cover that cost. When the replacement does not cost less to run, the result says there are no savings to pay it back. Past 50 years, it says it takes more than 50 years instead of giving a figure.

Cost per appliance and Compare a replacement each keep their own entries, so switching between them loses nothing. The rate is shared by both.

How it is calculated

The cost is the energy used in kWh multiplied by the rate in yen per kWh.

• Cost per hour = power (W) ÷ 1000 × rate × units
• Cost per day = power (W) ÷ 1000 × hours used per day × rate × units
• Cost per month = cost per day × days used per month
• Cost per year = cost per month × 12

With a yearly energy, the yearly cost is yearly energy × rate × units; a twelfth of it is shown as the month and a 365th as the average day.

The rate starts at 31 yen/kWh (tax included), the guide rate the Japanese appliance fair trade council (全国家庭電気製品公正取引協議会) set on 22 July 2022 for the electricity costs printed in appliance catalogs. Real rates depend on the supplier, the plan, and the usage tier. Enter the rate from your meter reading slip or bill for a figure closer to your own plan.

Nothing is rounded along the way; the final figures are rounded half up: the hour and the day to 0.1 yen, the month and the year to 1 yen, and energy to 0.01 kWh. Totals are rounded after adding the exact figures, so they may not match the sum of the rounded figures shown for each appliance. With many small appliances, the difference can be a few yen.

When comparing a replacement, the differences in cost and energy are worked out from the exact figures and then rounded at the same places, with halves rounded away from zero. They can therefore be 1 yen off the two rounded figures in the statement subtracted. The time to pay back is the cost of the replacement ÷ the saving per month, rounded up to a whole month. A month here is the Days used per month you entered, or a twelfth of a year for an appliance worked out from its yearly energy.

Example

At 31 yen/kWh, with these three appliances:

• Hair dryer: 1200 W, 10 minutes a day, 30 days
• Fridge: yearly energy of 300 kWh/year
• LED lights: 8 W, 6 hours a day, 30 days, 4 units

Hair dryer  186 yen a month (37.2 yen an hour, 6.2 yen a day, 6.00 kWh a month)
Fridge      775 yen a month (25.5 yen a day on average, 25.00 kWh a month)
LED lights  179 yen a month (1.0 yen an hour, 6.0 yen a day, 5.76 kWh a month)
Total       1,140 yen a month, 13,675 yen a year (36.76 kWh a month)

The fridge makes up 68.0% of the total, the hair dryer 16.3%, and the LED lights 15.7%. The hair dryer draws a lot of power but runs only briefly, so it costs less a month than the fridge, which runs all day.

With Compare a replacement, comparing two fridges at 31 yen/kWh:

• Current: yearly energy of 500 kWh/year
• Replacement: yearly energy of 270 kWh/year
• Cost of the replacement: 100,000 yen

Current      1,292 yen a month (15,500 yen a year, 41.67 kWh a month)
Replacement  698 yen a month (8,370 yen a year, 22.50 kWh a month)
Difference   −594 yen a month (−7,130 yen a year, −19.17 kWh a month)

The replacement saves 7,130 yen a year. 100,000 yen at about 594 yen a month is 168.3 months, so after 14 years and 1 month of use the savings cover 100,000 yen.

Notes

• The result is the energy used times the rate, as a guide. The basic or minimum charge of the plan, the fuel cost adjustment, and the renewable energy surcharge are not included.
• On a tiered plan, where the rate rises as you use more, extra usage can cost more than the average rate.
• Air conditioners, heaters, and microwaves draw very different power depending on the temperature and setting. The power on the label is often close to the maximum, so the real cost is usually lower.
• The time to pay back a replacement is a guide worked out from the difference in running cost alone. Add or subtract the recycling or disposal fee for the old appliance, or what repairs would have cost, in Cost of the replacement as you see fit.
• Everything you enter is calculated in your browser and is never sent or saved.

FAQ

Where do I find the power?

It is printed as "消費電力 ○○W" (power consumption) on the rating label on the back or bottom of the appliance, in the specifications of the manual, or in the maker's specification sheet online. For appliances with high and low settings, enter the figure for the setting you use.

I only know the amps (A). What do I enter?

On a Japanese household outlet (100 V), amps × 100 is roughly the power in watts. For 6 A, enter 600 W. When the power is given in kW, multiply it by 1000 (1.2 kW is 1200 W).

Can I work out the cost of standby power?

Add an appliance and enter its standby power (for example 0.5 W), 24 hours a day, and 30 days a month. Standby power is small, but it runs all day, so over a year it adds up to a noticeable amount.

Should I use the power on the label for an air conditioner?

An air conditioner draws less once the room nears the set temperature, so the power on the label overstates the cost. The catalog's seasonal energy (期間消費電力量, kWh) is a guide to the energy used over the cooling and heating seasons. Switch to By yearly energy and enter it for a guide to the yearly cost.

When does the 31 yen rate date from?

The council raised its guide rate from 27 yen/kWh to 31 yen/kWh on 22 July 2022. Older catalogs may show costs worked out at 27 yen. When comparing with a catalog, set the rate to the one it uses.