Annual kWh to Cost Calculator (EnergyGuide Label)

Enter the yearly kWh from the appliance's EnergyGuide label or spec sheet and your electricity rate. Enter the yearly kWh of a second appliance (Appliance B) to also see the cost difference when you replace or choose a model.

Appliance A yearly use (kWh/yr)

Electricity rate ($/kWh)

Appliance B yearly use (kWh/yr, optional)

Appliance A price ($, optional)

Appliance B price ($, optional)

The calculator uses 1 month = 1 year ÷ 12 and 1 day = 1 year ÷ 365. The yearly kWh on the label is measured under standard test conditions, so your real cost changes with how and where you use the appliance. The payback period is a simple result for the values you enter; it does not include discounts, rebates or changes in electricity rates.

Result and graph

Enter the yearly kWh from the label or spec sheet and your electricity rate in the fields on the left and press "Calculate". The result and a graph will appear here.

[ CLOSE ]

What you can do on this page
What is this calculation used for?
How to Use
Formulas and figures
Symbols and terms
- Symbols
- Terms
Good to know before you start
How to calculate it in Excel
How to calculate it in Google Sheets
How to calculate it in Python
How to write it in LaTeX and other math languages (copy and paste)
How to have ChatGPT do the calculation
DataChef Features
Related Features
NumberChef Calculators List

What you can do on this page

Enter the "Estimated Yearly Electricity Use" (kWh per year) from an appliance's EnergyGuide label or spec sheet and your electricity rate, and you get the cost and energy use per year, month and day on the spot
Enter the yearly kWh of a second appliance to compare the cost difference (per year, month and day, and over 10 years) between your old and new model, or between two models you are choosing from
Also enter the prices of the two models to see how many years the energy savings take to cover the price difference (the simple payback period)
A bar graph of the cost over 1, 5 and 10 years shows the difference at a glance
A plain-language explanation of the formulas and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page

The yearly kWh on an EnergyGuide label is measured under standard test conditions set by the U.S. Department of Energy, so your real cost depends on how and where you use the appliance and on the season. The "Estimated Yearly Energy Cost" on the label is found with the same formula as this calculator, "yearly kWh × rate", using a national average electricity price; the price used is printed in small type on the label. Your own rate depends on your state, utility and plan, so enter the rate from your electric bill. To estimate cost from an appliance's wattage and hours of use, use the related page "Electricity Cost Calculator (Appliance Energy Use and Cost)".

What is this calculation used for?

Put a number on the savings from a new refrigerator

A refrigerator runs 24 hours a day, 365 days a year, so the difference in yearly kWh becomes the difference in cost every year. For example, if you replace an older refrigerator that uses 450 kWh per year with a new model that uses 300 kWh, the difference is 150 kWh. At $0.17 per kWh, that is $25.50 a year, or $255 over 10 years (both are results for the values entered).
With the price of the appliance and the energy savings in the same unit, dollars, you can think about replacing it with numbers instead of feelings like "it still works" or "the new one is efficient". An old model may use more than its label says because of wear, so the real difference may be even larger.

Check what a bigger TV costs to run

A TV's yearly kWh usually goes up with screen size. For example, if a 55-inch model uses 100 kWh per year and a 75-inch model uses 200 kWh, the difference is 100 kWh, or $17 a year and about $1.42 a month at $0.17 per kWh (values differ by model).
Knowing how much more a bigger screen costs each month helps you decide calmly how much that difference matters to you. The yearly kWh on a TV's EnergyGuide label assumes a set number of viewing hours per day, printed on the label, so if you watch more than that, the real use will be higher.

Estimate the monthly cost when you set up a new home

When you move into a new place, add up the yearly kWh on the labels to get a rough monthly cost for your appliances. For example, a refrigerator (400 kWh/yr), a chest freezer (250 kWh/yr) and a TV (100 kWh/yr) come to 750 kWh per year. At $0.17 per kWh, that is $127.50 a year, or about $10.63 a month for these three.
Your real bill also includes the customer charge and the cost of lighting, heating and cooling, and cooking, so it will be higher. Still, knowing "the appliances that are always on cost about this much" gives you a base for planning your budget.

Turn the label's yearly cost into the cost at your rate

The Estimated Yearly Energy Cost on an EnergyGuide label is the yearly kWh times a national average price printed on the label. If your rate is different, your cost is different too. For example, a refrigerator that uses 300 kWh per year costs $51 a year at $0.17 per kWh, but $90 a year where electricity costs $0.30 per kWh, as in some parts of the country.
You can find your rate on your electric bill or on your utility's website. Dividing the total of your bill by the kWh used gives a rough "real rate" that also includes the customer charge and other charges.

Turn energy use per load into a yearly value

Some appliances list energy use per load instead of per year, and electric clothes dryers do not carry an EnergyGuide label at all. In that case, multiply the energy per load by the number of loads to get a yearly value. For example, if an electric dryer uses 3 kWh per load and you run 4 loads a week, 3 × 4 × 52 = 624 kWh per year, or about $106.08 a year at $0.17 per kWh.
With this formula you can also put a price on habits, such as "how much does one dryer load cost" or "how much do I save a year by hanging clothes to dry on some days".

Compare a standard electric water heater with a heat pump water heater

Water heaters carry an EnergyGuide label, and the yearly kWh of a standard electric tank and a heat pump (hybrid) water heater are very different. For example, if a standard model uses 4,500 kWh per year and a heat pump model uses 1,300 kWh, the difference is 3,200 kWh, or $544 a year at $0.17 per kWh (values differ by model).
A heat pump water heater usually costs more to buy. If it costs $1,200 more, dividing by $544 a year gives a simple payback period of about 2.2 years. Rebates and tax credits can shorten it further. Comparing this number with how many years you plan to use the heater is the basic way to include energy cost when you choose a model.

Formulas and figures

Cost per year ($)

Figure

Standard notation (the usual math form)

$C$ $=$ $E$ $\times$ $u$

In words (symbols replaced with words)

③ $C$: cost per year ($) $=$ ① $E$: yearly energy use (kWh/yr) $\times$ ② $u$: electricity rate ($/kWh)

The formula in words

① Take the $E$: yearly energy use (kWh/yr)

② multiply it by the $u$: electricity rate ($/kWh)

③ and you get the $C$: cost per year ($)

Quick example

The cost per year of a refrigerator whose label says 300 kWh per year, at a rate of $0.17 per kWh, is

$C$: cost per year ($) $=$ yearly energy use (300 kWh/yr) $\times$ rate ($0.17/kWh)

$300 \times 0.17 = 51$

Key idea

The "Estimated Yearly Electricity Use" on an EnergyGuide label is the electricity (kWh) the appliance uses in one year, measured with a standard test method set by the U.S. Department of Energy. Its unit, kWh per year, stands for "energy per year", so multiplying it by the price of 1 kWh ($/kWh) gives the cost for a year directly. Unlike the related page "Electricity Cost Calculator (Appliance Energy Use and Cost)", you do not need to multiply wattage by hours of use to get kWh. The "Estimated Yearly Energy Cost" in large type on the label is also found with this formula, using a national average electricity price that is printed on the label. If your own rate is different, just put it into this calculator to turn the label's number into the cost for your home.

Cost per month and per day ($)

Standard notation (the usual math form)

$C_{\text{month}}$ $=$ $E$ $\times$ $u$ $\div$ $12$

$C_{\text{day}}$ $=$ $E$ $\times$ $u$ $\div$ $365$

In words (symbols replaced with words)

④ $C_{\text{month}}$: cost per month ($) $=$ ① $E$: yearly energy use (kWh/yr) $\times$ ② $u$: electricity rate ($/kWh) $\div$ ③ 12 (months in a year)

⑥ $C_{\text{day}}$: cost per day ($) $=$ $E$: yearly energy use (kWh/yr) $\times$ $u$: electricity rate ($/kWh) $\div$ ⑤ 365 (days in a year)

The formula in words

① Multiply the $E$: yearly energy use (kWh/yr)

② by the $u$: electricity rate ($/kWh) to get the cost per year,

③ divide it by 12 (months in a year)

④ to get the $C_{\text{month}}$: cost per month ($) , and divide the same yearly cost by

⑤ 365 (days in a year)

⑥ to get the $C_{\text{day}}$: cost per day ($)

Quick example

For the refrigerator that uses 300 kWh per year (a rate of $0.17/kWh, so $51 a year), the cost per month and per day are

cost per month ($) $=$ yearly energy use (300 kWh/yr) $\times$ rate ($0.17/kWh) $\div$ 12 (months)

$300 \times 0.17 \div 12 = 51 \div 12 = 4.25$

$300 \times 0.17 \div 365 = 51 \div 365 \approx 0.14$

Key idea

The yearly kWh is a value for one whole year, so divide by 12 for one month and by 365 for one day. The same goes for energy use: $300 \div 12 = 25$ kWh is one month and $300 \div 365 \approx 0.82$ kWh is one day. These monthly and daily values are averages, the yearly total split evenly. Refrigerators and air conditioners use electricity very differently in summer and winter, so the real cost in some months is above this average and in others below it.

Yearly cost difference between two appliances ($)

Figure

Standard notation (the usual math form)

$\Delta C$ $=$ $($ $E_{\mathrm{A}}$ $-$ $E_{\mathrm{B}}$ $)$ $\times$ $u$

In words (symbols replaced with words)

④ $\Delta C$: yearly cost difference ($) $=$ $($ ① $E_{\mathrm{A}}$: yearly use of Appliance A (kWh/yr) $-$ ② $E_{\mathrm{B}}$: yearly use of Appliance B (kWh/yr) $)$ $\times$ ③ $u$: electricity rate ($/kWh)

The formula in words

① From the $E_{\mathrm{A}}$: yearly use of Appliance A (kWh/yr)

② subtract the $E_{\mathrm{B}}$: yearly use of Appliance B (kWh/yr) to get the difference in energy per year,

③ multiply it by the $u$: electricity rate ($/kWh)

④ and you get the $\Delta C$: yearly cost difference ($) (if it is negative, Appliance A costs less)

Quick example

When you replace an old refrigerator (Appliance B, 450 kWh/yr) with a new one (Appliance A, 300 kWh/yr), the yearly cost difference at $0.17 per kWh is

$\Delta C$: yearly cost difference ($) $=$ $($ Appliance A (300 kWh/yr) $-$ Appliance B (450 kWh/yr) $)$ $\times$ rate ($0.17/kWh)

$(300 - 450) \times 0.17 = -150 \times 0.17 = -25.5$

Key idea

A negative difference tells you that Appliance A costs $25.50 less per year. This calculator states the direction in words (which one costs less) and shows the amount as an absolute value (without the minus sign). You get the same answer whether you find each appliance's yearly cost first and subtract ($300 \times 0.17 - 450 \times 0.17 = 51 - 76.5 = -25.5$) or find the difference in energy first and then multiply by the rate. This is the distributive property ($(a - b) \times u = a \times u - b \times u$). The yearly kWh is measured under standard conditions, so if both appliances are used the same way in the same place, the difference between them is a good guide to the real cost difference. However, an old appliance may use more electricity than its label says because of wear, and then the real difference can be larger than calculated.

Simple payback period (years)

Standard notation (the usual math form)

$Y$ $=$ $\Delta P$ $\div$ $\Delta C$

In words (symbols replaced with words)

③ $Y$: simple payback period (years) $=$ ① $\Delta P$: price difference ($) $\div$ ② $\Delta C$: yearly cost difference ($)

The formula in words

① Take the $\Delta P$: price difference (how much more the model with the lower energy cost costs to buy)

② divide it by the $\Delta C$: yearly cost difference ($)

③ and you get the $Y$: simple payback period (years)

Quick example

If model A costs less to run and sells for $1,000, model B costs more to run and sells for $850, and the yearly cost difference is $25.50, the years it takes to earn back the price difference are

$Y$: simple payback period (years) $=$ price difference (1000 − 850 = $150) $\div$ yearly cost difference ($25.50)

$150 \div 25.5 \approx 5.9$

Key idea

The simple payback period only asks how many years of energy savings the price difference equals. It does not include discounts, rebates, tax credits, changes in electricity rates, the risk of breakdowns or disposal costs. Read it as "the result for the values you entered": if you use the appliance longer than this, the energy savings are larger than the price difference. If the model with the lower energy cost is also the same price or cheaper to buy, there is no difference to earn back, so there is no need to think about a payback period (this calculator tells you so). When you compare with the model you already own, enter its price as $0. The result is then the years it takes for the energy savings to pay for the new model.

Multiply the yearly kWh on the EnergyGuide label by your electricity rate ($/kWh) and you get the cost for one year. Divide by 12 for a month and by 365 for a day. To compare two appliances, multiply the difference in yearly kWh by the rate to get the yearly cost difference, and divide the price difference by that amount to estimate how many years it takes to earn it back (the simple payback period).

Symbols and terms

Symbols

$E$		Yearly energy use. The electricity the appliance uses in one year, in kWh per year. From the word "energy". It is shown on the EnergyGuide label and in spec sheets.
$E_{\mathrm{A}},\ E_{\mathrm{B}}$		The yearly energy use (kWh/yr) of Appliance A and Appliance B when you compare two. The small A and B at the lower right are subscripts that show which appliance the value belongs to.
$u$		Electricity rate. The price of 1 kWh ($/kWh). From "unit price". It depends on your utility and plan.
$C$		Cost per year ($). From the word "cost".
$C_{\text{month}},\ C_{\text{day}}$		The cost per month and per day ($). The words "month" and "day" at the lower right are subscripts that show the period. They are the yearly cost $C$ divided by 12 and by 365.
$\Delta$	delta	The Greek capital letter delta, used for "difference" or "change". It is said to come from D, as in "difference". $\Delta C$ is read "the difference in cost $C$".
$\Delta C$	delta C	The yearly cost difference between two appliances ($). Appliance A's yearly cost minus Appliance B's. If it is negative, Appliance A costs less.
$\Delta P$	delta P	The price difference between two appliances ($). P is from "price". It is how much more the model with the lower energy cost costs to buy.
$Y$		Simple payback period (years). From the word "year". A rough guide to how many years the energy savings take to cover the price difference.
$\approx$	approximately equal to	The symbol for "approximately equal to". It is used to show a rounded value when a division does not come out even (for example, $51 \div 365 \approx 0.14$).

Terms

Estimated Yearly Electricity Use	The electricity (kWh per year) an appliance uses in one year, as shown on the EnergyGuide label. It is measured with a standard test method set by the U.S. Department of Energy (DOE); for example, a refrigerator is tested with a set room temperature and set compartment temperatures. Because it is "the value under standard conditions", real use goes up or down with how and where you use the appliance and the season. Think of it as a ruler for comparing models under the same conditions.
EnergyGuide label	The yellow label required by the Federal Trade Commission (FTC) on many home appliances, such as refrigerators, freezers, dishwashers, clothes washers, water heaters, room air conditioners and TVs. It shows the Estimated Yearly Energy Cost, a bar with the cost range of similar models, and usually the Estimated Yearly Electricity Use in kWh. The yearly kWh used on this page comes from this label or the spec sheet.
Estimated Yearly Energy Cost	The dollar amount in large type on the EnergyGuide label, a rough guide to what the appliance costs to run for a year. It is the yearly kWh times a national average electricity price printed on the label, the same calculation as formula 1 on this page. If your rate is different, enter your rate in this calculator to get the cost for your home.
Label electricity price	The electricity price the FTC sets for calculating the cost on EnergyGuide labels, so that every label uses the same price. It is updated from time to time, and the value used is printed on the label. Your real rate depends on your state, utility, plan and usage.
ENERGY STAR	A program run by the U.S. Environmental Protection Agency (EPA) that certifies products that use less energy than set levels. Certified models carry the ENERGY STAR logo, and the logo may also appear on the EnergyGuide label.
Cost range of similar models	The bar on the EnergyGuide label that shows where this model's yearly cost sits between the lowest and highest cost among similar models (similar size and features). The further left the marker, the less energy the model uses compared with similar models.
kWh (kilowatt-hour)	The unit of energy, or the total amount of electricity used. Using 1 kW (1000 W) of power for 1 hour uses 1 kWh, and electric bills are based on kWh. "300 kWh per year" is the same amount of electricity as running a 1000 W appliance for 300 hours in a year.
Wattage	The power (W) an appliance uses at any moment while it runs. It is a rate, not an amount, so to get a cost you first multiply it by hours of use to get kWh (the formula on the related electricity cost page). Yearly kWh, on the other hand, is already an amount for one year, so you only multiply it by the rate.
DOE test procedure	The standard test method, set by the U.S. Department of Energy for each kind of appliance, used to measure the energy use shown on labels and spec sheets. Because every model is tested the same way, you can compare their yearly kWh fairly.
Energy use per load	The electricity (Wh or kWh) used for one run of an appliance such as a clothes dryer or a dishwasher. To get a yearly value, multiply it by the number of runs in a year (for example 3 kWh × 4 loads a week × 52 weeks = 624 kWh per year). If it is given in Wh, divide by 1000 to change it into kWh before you enter it.
Simple payback period	The extra upfront cost (here, the price difference) divided by the yearly savings (here, the yearly cost difference). It is the simplest guide to "how many years until it pays for itself", and it ignores discounts, rate changes and the time value of money. The general form of this calculation is on the related page "Payback Period Calculator".
Distributive property	The rule that when you multiply a sum or difference in parentheses by a number, you can multiply each number inside first and then add or subtract, and get the same result, as in $(a - b) \times u = a \times u - b \times u$. It is why "difference in energy × rate" and "difference of the two costs" give the same answer.
Wear with age	The loss of performance over years of use, from worn parts, dirt and similar causes. An old refrigerator or air conditioner may use more electricity than its label says, and then the real savings from replacing it are larger than the difference between the label values.

Good to know before you start

Here is what helps you understand the calculations on this page, not just use them.
If you get stuck, going back over the topics in this table is the quickest way forward.

Multiplying and dividing decimals (Grade 5)	You can multiply such as $300 \times 0.17$, and round the answer to a division that does not come out even, such as $51 \div 365$ You know that splitting a total evenly gives an average, such as "one year divided by 12 is one month"
Converting units (Grades 4 to 7)	You know that the prefix k (kilo) stands for 1000 times, so $1\,\mathrm{kWh} = 1000\,\mathrm{Wh}$ You can build a formula by paying attention to units, such as "3 kWh per load × 200 loads a year"
Power and energy (middle school physical science)	You can tell power (W, how fast electricity is used) from energy (Wh or kWh, the total amount used) You know that yearly kWh is the energy for one year and is not the same thing as power (W)
Positive and negative numbers (Grade 6 to 7)	You can do a subtraction whose answer is negative, such as $300 - 450 = -150$ You can tell what a negative difference says (the first number is the smaller one)
The distributive property (Grades 6 to 7)	You can multiply a difference in parentheses by a number, as in $(a - b) \times u = a \times u - b \times u$

How to calculate it in Excel

Copy the whole table below and paste it into cell A1 in Excel. It works as is.

Table for cost per year

Yearly energy use (kWh/yr)	300
Electricity rate ($/kWh)	0.17
Cost per year ($)	=B1*B2

Table for cost per month and per day

Yearly energy use (kWh/yr)	300
Electricity rate ($/kWh)	0.17
Energy use per month (kWh)	=B1/12
Cost per month ($)	=B1*B2/12
Energy use per day (kWh)	=B1/365
Cost per day ($)	=B1*B2/365

Table for the yearly cost difference between two appliances

Appliance A yearly use (kWh/yr)	300
Appliance B yearly use (kWh/yr)	450
Electricity rate ($/kWh)	0.17
Yearly cost difference ($, negative if A costs less)	=(B1-B2)*B3
Difference over 10 years ($)	=B4*10

Table for the simple payback period

Price of the model with lower energy cost ($)	1000
Price of the other model ($)	850
Yearly cost difference ($, absolute value)	25.5
Price difference ($)	=B1-B2
Simple payback period (years)	=B4/B3

After you paste it, the upper cells in column B are the inputs and the green formula cells show the results automatically.
The first table is the example of 300 kWh/yr at $0.17/kWh, and B3 shows 51 ($). The second table changes the same values into a month and a day: the cost per month (B4) is $4.25 and the cost per day (B6) is about $0.14.
The third table is the difference between two appliances, and B4 shows -25.5 ($). The minus sign tells you that Appliance A costs less. The fourth table finds how long a yearly difference of $25.50 takes to cover a price difference of $150, and B5 shows about 5.88 (years). Just change the numbers in column B to your own appliances' values.

How to calculate it in Google Sheets

Copy the whole table below and paste it into cell A1 in Google Sheets. It works as is.

Table for cost per year

Yearly energy use (kWh/yr)	300
Electricity rate ($/kWh)	0.17
Cost per year ($)	=B1*B2

Table for cost per month and per day

Yearly energy use (kWh/yr)	300
Electricity rate ($/kWh)	0.17
Energy use per month (kWh)	=B1/12
Cost per month ($)	=B1*B2/12
Energy use per day (kWh)	=B1/365
Cost per day ($)	=B1*B2/365

Table for the yearly cost difference between two appliances

Appliance A yearly use (kWh/yr)	300
Appliance B yearly use (kWh/yr)	450
Electricity rate ($/kWh)	0.17
Yearly cost difference ($, negative if A costs less)	=(B1-B2)*B3
Difference over 10 years ($)	=B4*10

Table for the simple payback period

Price of the model with lower energy cost ($)	1000
Price of the other model ($)	850
Yearly cost difference ($, absolute value)	25.5
Price difference ($)	=B1-B2
Simple payback period (years)	=B4/B3

The formulas use only multiplication, division and subtraction, so the same formulas as in Excel work as they are. Copy the whole table, paste it into cell A1, and change the numbers in column B to your own.

How to calculate it in Python

annual_kwh_a = 300        # Appliance A yearly energy use (kWh/yr)
annual_kwh_b = 450        # Appliance B yearly energy use (kWh/yr). None if not comparing
price_per_kwh = 0.17      # Electricity rate ($/kWh)
body_price_a = 1000       # Appliance A price ($). None if you do not need the payback period
body_price_b = 850        # Appliance B price ($)

# Cost per year = yearly kWh x rate. Divide by 12 for a month and by 365 for a day
annual_cost_a = annual_kwh_a * price_per_kwh
print(f"Appliance A, 1 year: {annual_kwh_a} kWh / ${annual_cost_a:.2f}")
print(f"Appliance A, 1 month: {annual_kwh_a / 12:.1f} kWh / ${annual_cost_a / 12:.2f}")
print(f"Appliance A, 1 day: {annual_kwh_a / 365:.2f} kWh / ${annual_cost_a / 365:.2f}")

if annual_kwh_b is not None:
    # Difference = (A - B) x rate. Negative means Appliance A costs less
    cost_diff = (annual_kwh_a - annual_kwh_b) * price_per_kwh
    cheaper = "Appliance A" if cost_diff < 0 else "Appliance B"
    print(f"Yearly cost difference: ${abs(cost_diff):.2f} ({cheaper} costs less)")
    print(f"Difference over 10 years: ${abs(cost_diff) * 10:.2f}")

    if body_price_a is not None and cost_diff != 0:
        # Simple payback = extra price of the cheaper-to-run model / yearly difference
        cheaper_price, other_price = (body_price_a, body_price_b) if cost_diff < 0 else (body_price_b, body_price_a)
        extra_price = cheaper_price - other_price
        if extra_price > 0:
            print(f"Simple payback period: {extra_price / abs(cost_diff):.1f} years")
        else:
            print("The cheaper-to-run model is also the same price or cheaper, so no payback period is needed")

It runs with the standard library only. Change the first 5 values (the yearly kWh of the two appliances, the rate and the two prices) to your own and run it. To calculate one appliance only, set annual_kwh_b to None.

How to write it in LaTeX and other math languages (copy and paste)

Cost per year ($)

C = E × u

C = E \times u

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>C</mi>
    <mo>=</mo>
    <mi>E</mi>
    <mo>&#xD7;</mo>
    <mi>u</mi>
  </mrow>
</math>

C = E * u

annualCost = annualKwh*unitPrice

annualCost := E*u;

C = E*u;

C = E×u

Cost per month and per day ($)

C_month = E × u ÷ 12,  C_day = E × u ÷ 365

C_{\text{month}} = \frac{E \times u}{12}, \quad C_{\text{day}} = \frac{E \times u}{365}

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <msub><mi>C</mi><mtext>month</mtext></msub>
    <mo>=</mo>
    <mfrac><mrow><mi>E</mi><mo>&#xD7;</mo><mi>u</mi></mrow><mn>12</mn></mfrac>
    <mo>,</mo>
    <msub><mi>C</mi><mtext>day</mtext></msub>
    <mo>=</mo>
    <mfrac><mrow><mi>E</mi><mo>&#xD7;</mo><mi>u</mi></mrow><mn>365</mn></mfrac>
  </mrow>
</math>

C_"month" = (E * u) / 12, C_"day" = (E * u) / 365

monthlyCost = annualKwh*unitPrice/12; dailyCost = annualKwh*unitPrice/365

monthlyCost := E*u/12; dailyCost := E*u/365;

C_month = E*u/12; C_day = E*u/365;

C_month = (E×u)/12, C_day = (E×u)/365

Yearly cost difference between two appliances ($)

ΔC = (E_A − E_B) × u

\Delta C = (E_{\mathrm{A}} - E_{\mathrm{B}}) \times u

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>&#x394;</mi><mi>C</mi>
    <mo>=</mo>
    <mo>(</mo>
    <msub><mi>E</mi><mi mathvariant="normal">A</mi></msub>
    <mo>&#x2212;</mo>
    <msub><mi>E</mi><mi mathvariant="normal">B</mi></msub>
    <mo>)</mo>
    <mo>&#xD7;</mo>
    <mi>u</mi>
  </mrow>
</math>

Delta C = (E_A - E_B) * u

costDiff = (annualKwhA - annualKwhB)*unitPrice

costDiff := (E_A - E_B)*u;

dC = (E_A - E_B)*u;

ΔC = (E_A − E_B)×u

Simple payback period (years)

Y = ΔP ÷ ΔC

Y = \frac{\Delta P}{\Delta C}

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>Y</mi>
    <mo>=</mo>
    <mfrac>
      <mrow><mi>&#x394;</mi><mi>P</mi></mrow>
      <mrow><mi>&#x394;</mi><mi>C</mi></mrow>
    </mfrac>
  </mrow>
</math>

Y = (Delta P) / (Delta C)

paybackYears = priceDiff/costDiff

paybackYears := priceDiff/costDiff;

Y = dP/dC;

Y = ΔP/ΔC

How to have ChatGPT do the calculation

You are an electricity cost assistant. Do the calculation below by actually running Python code, and base your answer only on the numbers from the output (do not calculate in your head or guess).

There is a refrigerator whose EnergyGuide label says 300 kWh per year (Appliance A, price $1,000) and one that says 450 kWh per year (Appliance B, price $850). The electricity rate is $0.17 per kWh.
Find the cost per year with "yearly kWh × rate ($/kWh)", the cost per month by dividing that by 12, and the cost per day by dividing it by 365.
Find each of the following.
1. Appliance A's cost ($) and energy use (kWh) per year, per month and per day
2. The yearly cost difference between the two ($) and which one costs less
3. How many years it takes for the yearly difference to cover the extra price of the model that costs less to run (the simple payback period)

Show the formulas you used and the numbers from the output.

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\(E\)		Yearly energy use. The electricity the appliance uses in one year, in kWh per year. From the word "energy". It is shown on the EnergyGuide label and in spec sheets.
\(E_{\mathrm{A}},\ E_{\mathrm{B}}\)		The yearly energy use (kWh/yr) of Appliance A and Appliance B when you compare two. The small A and B at the lower right are subscripts that show which appliance the value belongs to.
\(u\)		Electricity rate. The price of 1 kWh ($/kWh). From "unit price". It depends on your utility and plan.
\(C\)		Cost per year ($). From the word "cost".
\(C_{\text{month}},\ C_{\text{day}}\)		The cost per month and per day ($). The words "month" and "day" at the lower right are subscripts that show the period. They are the yearly cost \(C\) divided by 12 and by 365.
\(\Delta\)	delta	The Greek capital letter delta, used for "difference" or "change". It is said to come from D, as in "difference". \(\Delta C\) is read "the difference in cost \(C\)".
\(\Delta C\)	delta C	The yearly cost difference between two appliances ($). Appliance A's yearly cost minus Appliance B's. If it is negative, Appliance A costs less.
\(\Delta P\)	delta P	The price difference between two appliances ($). P is from "price". It is how much more the model with the lower energy cost costs to buy.
\(Y\)		Simple payback period (years). From the word "year". A rough guide to how many years the energy savings take to cover the price difference.
\(\approx\)	approximately equal to	The symbol for "approximately equal to". It is used to show a rounded value when a division does not come out even (for example, \(51 \div 365 \approx 0.14\)).

Multiplying and dividing decimals (Grade 5)	You can multiply such as \(300 \times 0.17\), and round the answer to a division that does not come out even, such as \(51 \div 365\) You know that splitting a total evenly gives an average, such as "one year divided by 12 is one month"
Converting units (Grades 4 to 7)	You know that the prefix k (kilo) stands for 1000 times, so \(1\,\mathrm{kWh} = 1000\,\mathrm{Wh}\) You can build a formula by paying attention to units, such as "3 kWh per load × 200 loads a year"
Power and energy (middle school physical science)	You can tell power (W, how fast electricity is used) from energy (Wh or kWh, the total amount used) You know that yearly kWh is the energy for one year and is not the same thing as power (W)
Positive and negative numbers (Grade 6 to 7)	You can do a subtraction whose answer is negative, such as \(300 - 450 = -150\) You can tell what a negative difference says (the first number is the smaller one)
The distributive property (Grades 6 to 7)	You can multiply a difference in parentheses by a number, as in \((a - b) \times u = a \times u - b \times u\)

Annual kWh to Cost Calculator (EnergyGuide Label)

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How to have ChatGPT do the calculation

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