Choose "Find the bill from kWh" or "Find kWh from a budget", then enter the kWh used (or your budget) and the rates of your plan. For a tiered plan, choose "Tiered" under "Rate type" to show the fields for each tier.
If there is no customer charge or per-kWh charge, leave those fields blank (0). For a plan with only 2 tiers, leave the Tier 2 limit blank.
Result and graph
Enter the kWh you used and your rates in the fields on the left and press "Calculate". The total bill, the breakdown by tier and a graph will appear here.
Table of Contents
-
What you can do on this page
-
What is this calculation used for?
-
How to Use
-
Formula
-
Symbols and terms
-
Good to know before you start
-
How to calculate it in Excel
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How to calculate it in Google Sheets
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How to calculate it in Python
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How to write it in LaTeX and other math languages (copy and paste)
-
How to have ChatGPT do the calculation
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DataChef Features
-
Related Features
-
NumberChef Calculators List
What you can do on this page
- Enter the kWh shown on your electric bill or your utility account and the rates of your plan, and you get the total bill for that month on the spot
- Tiered rates such as "first 500 kWh at one price, up to 1,000 kWh at another, and more above that" are supported (up to 3 tiers). You also see the kWh and cost in each tier, and the effective rate (the total divided by the kWh, or what you really pay per kWh)
- You can add a monthly customer charge and other per-kWh charges, such as a fuel adjustment charge or delivery charges (a negative value is allowed for credits)
- To keep your bill under a set amount, switch to the reverse mode to find how many kWh your budget allows (with tiered rates, the tiers are filled in order for an exact answer)
- A line graph shows how the bill grows with usage. With tiered rates, you can see the slope (the rate) change at each tier boundary
The rates, tier limits and customer charge are all inputs; this calculator does not store the prices of any particular utility or plan. You can find your rates on your electric bill or on your utility's website. The tier limits and prices in the examples (500 kWh and 1,000 kWh) only show the typical shape of a tiered rate. Some plans also change the rate by season or by time of day; for a time-of-use plan, calculate each period separately. To estimate the cost of an appliance from its wattage and hours of use, use the related page "Electricity Cost Calculator (Appliance Energy Use and Cost)".
What is this calculation used for?
Check the breakdown of your electric bill yourself
Your bill shows the kWh used and the amount due, but you only see why it comes to that amount when you work out the breakdown. For example, with 1,200 kWh, a $12 customer charge, tiered rates ($0.12 for the first 500 kWh, $0.14 up to 1,000 kWh, $0.16 above that) and other charges of $0.03/kWh, the bill is an energy charge of $162 + other charges of $36 + a customer charge of $12 = $210.
Once you can work out the breakdown yourself, you can tell why a bill went up, for example "the fuel adjustment charge went up" or "usage reached Tier 3", and understand the change. (The real bill may differ by a few cents because of rounding, taxes and fees.)
Set an electricity budget for your first apartment
Once you decide "I want to keep electricity under $100 a month", work backward to find how many kWh that allows. Then you can check your usage in your utility account during the month. For example, with a $12 customer charge, a flat rate of $0.15/kWh and other charges of $0.02/kWh, the limit is \((100 - 12) \div 0.17 \approx 517.6\) kWh.
A goal in kWh instead of dollars lets you track a number you control, your usage, even if the rates change.
Estimate savings correctly with the top tier's price
With tiered rates, the kWh you cut come off the top tier (the highest price) first. If a home that uses 1,200 kWh cuts 100 kWh by using the air conditioner less, the cut comes from Tier 3, so the savings are \(100 \times (0.16 + 0.03) = 19\) dollars. That is more than the $17.50 you would get with the average effective rate ($0.175/kWh).
On the other hand, if a home stays within Tier 1 (for example 400 kWh) and cuts 50 kWh, it saves only the Tier 1 price, \(50 \times (0.12 + 0.03) = 7.50\) dollars. With this formula you can see in numbers that the same cut saves more in a home that uses a lot, which helps you decide what to do first.
Estimate the savings from new appliances or rooftop solar
Replacing appliances with efficient ones, or using power from your own solar panels, cuts the kWh you buy from the utility. The money saved is "kWh cut × the price those kWh were charged at (plus other charges)". For example, if you cut 150 kWh a month and those kWh were in Tier 3 ($0.16/kWh) plus other charges of $0.03/kWh, you save \(150 \times 0.19 = 28.50\) dollars a month, or $342 a year.
This estimate is the result for the rates and usage you entered. In reality it changes with seasonal usage, rate changes and how your utility credits solar power (net metering rules differ by state). Allow a margin over several years when you decide.
Split the bill fairly among roommates
If there is one meter for the home and you only know each person's kWh from submeters or smart plugs, be careful how you split the money. With tiered rates, splitting the bill "by share of kWh" can give the heavy user too much of the cheap tiers, or put too much of the customer charge on one person.
One fair way is to multiply each person's kWh by the overall effective rate (bill ÷ total kWh). With this method, everyone shares the customer charge and the tier differences on average. It gives you a common starting point when you talk about how to split the bill.
Compare electricity plans at the same usage
If you compare plans only by "the lowest rate", the ranking can flip because of the customer charge or the tier limits. Fix your own usage (for example 900 kWh), calculate the total bill for each plan with its customer charge, rates and tiers, and line them up by effective rate ($/kWh) for a fair comparison. In states where you can choose an electricity supplier, this is also a good way to compare offers.
Do the calculation for both a low-use month and a high-use month to see seasonal differences, such as "cheaper in summer and winter but more expensive in spring and fall". Rates change, so compare at current rates and check again from time to time.
Formula
Bill with a flat rate
Standard notation
(the usual math form)
\(C\)
\(=\)
\(E\)
\(\times\)
\((\)
\(u\)
\(+\)
\(a\)
\()\)
\(+\)
\(B\)
In words
(symbols replaced with words)
⑤
\(C\): total bill ($)
\(=\)
①
\(E\): electricity used (kWh)
\(\times\)
\((\)
②
\(u\): rate ($/kWh)
\(+\)
③
\(a\): other per-kWh charges ($/kWh)
\()\)
\(+\)
④
\(B\): customer charge ($)
The formula in words
①
Take the
\(E\): electricity used (kWh)
②
multiply it by what you really pay per kWh, which is the
\(u\): rate ($/kWh)
③
plus the
\(a\): other per-kWh charges ($/kWh)
④
then add the
\(B\): customer charge ($)
⑤
and you get the
\(C\): total bill ($)
Quick example
With 900 kWh used, a rate of $0.14/kWh, other per-kWh charges of $0.03/kWh and a customer charge of $12, the bill is
\(C\): total bill ($)
\(=\)
electricity used (900 kWh)
\(\times\)
\((\)
rate ($0.14/kWh)
\(+\)
other charges ($0.03/kWh)
\()\)
\(+\)
customer charge ($12)
\(900 \times (0.14 + 0.03) + 12 = 153 + 12 = 165\)
Key idea
An electric bill has two main parts: a fixed part you pay no matter how much you use (the customer charge) and a part that grows in proportion to your usage. The amount per kWh in the second part is not only the rate \(u\) of your plan. It is \(u + a\), where \(a\) includes other charges added per kWh, such as a fuel adjustment charge, delivery (transmission and distribution) charges and riders. These charges can change from month to month, and some can be negative (a credit), so use the values on that month's bill.
If your plan has no other per-kWh charges (or you want to ignore them), use \(a = 0\). If there is no customer charge, use \(B = 0\). The formula still works as it is.
Energy charge with tiered rates (sum of the tiers)
Standard notation
(the usual math form)
\(F\)
\(=\)
\(E_1\)
\(\times\)
\(u_1\)
\(+\)
\(E_2\)
\(\times\)
\(u_2\)
\(+\)
\(E_3\)
\(\times\)
\(u_3\)
In words
(symbols replaced with words)
⑦
\(F\): energy charge ($)
\(=\)
①
\(E_1\): kWh in Tier 1
\(\times\)
②
\(u_1\): Tier 1 rate
\(+\)
③
\(E_2\): kWh in Tier 2
\(\times\)
④
\(u_2\): Tier 2 rate
\(+\)
⑤
\(E_3\): kWh in Tier 3
\(\times\)
⑥
\(u_3\): Tier 3 rate
The formula in words
①
Multiply the
\(E_1\): kWh in Tier 1
②
by the
\(u_1\): Tier 1 rate ($/kWh)
(the Tier 1 charge),
③
multiply the
\(E_2\): kWh in Tier 2
④
by the
\(u_2\): Tier 2 rate ($/kWh)
(the Tier 2 charge),
⑤
multiply the
\(E_3\): kWh in Tier 3
⑥
by the
\(u_3\): Tier 3 rate ($/kWh)
(the Tier 3 charge), and add all three to get the
⑦
\(F\): energy charge ($)
Quick example
For 1,200 kWh on the tiered rate "first 500 kWh at $0.12/kWh, up to 1,000 kWh at $0.14/kWh, over 1,000 kWh at $0.16/kWh", the kWh in each tier are 500, 500 and 200, so
\(F\): energy charge ($)
\(=\)
Tier 1 (500 kWh)
\(\times\)
$0.12/kWh
\(+\)
Tier 2 (500 kWh)
\(\times\)
$0.14/kWh
\(+\)
Tier 3 (200 kWh)
\(\times\)
$0.16/kWh
\(500 \times 0.12 + 500 \times 0.14 + 200 \times 0.16 = 60 + 70 + 32 = 162\)
Key idea
The most common mistake with tiered rates is to think that "if I use 1,200 kWh, every kWh is charged at the Tier 3 price of $0.16". In fact, usage is stacked up from the lowest tier, and each tier's rate applies only to the kWh that fall in that tier (the same way the US federal income tax brackets work). If the Tier 1 limit is \(L_1\) and the Tier 2 limit is \(L_2\), the kWh in each tier are
\(E_1 = \min(E,\ L_1)\), \(E_2 = \min(E,\ L_2) - L_1\) (0 if negative), \(E_3 = E - L_2\) (0 if negative).
For example, with \(E = 1200\), \(L_1 = 500\) and \(L_2 = 1000\), you get \(E_1 = 500\), \(E_2 = 1000 - 500 = 500\) and \(E_3 = 1200 - 1000 = 200\). If usage does not reach the Tier 1 limit (for example \(E = 400\)), then \(E_1 = 400\) and \(E_2 = E_3 = 0\).
A plan with only 2 tiers works with the same formula by using \(E_3 = 0\) (no upper limit on Tier 2).
Total bill and effective rate
Standard notation
(the usual math form)
\(C\)
\(=\)
\(F\)
\(+\)
\(a\)
\(\times\)
\(E\)
\(+\)
\(B\)
\(\bar{u}\)
\(=\)
\(C\)
\(\div\)
\(E\)
In words
(symbols replaced with words)
④
\(C\): total bill ($)
\(=\)
①
\(F\): energy charge ($)
\(+\)
②
\(a\): other per-kWh charges ($/kWh)
\(\times\)
\(E\): electricity used (kWh)
\(+\)
③
\(B\): customer charge ($)
⑥
\(\bar{u}\): effective rate ($/kWh)
\(=\)
⑤
\(C\): total bill ($)
\(\div\)
\(E\): electricity used (kWh)
The formula in words
①
Take the
\(F\): energy charge ($)
②
add the
\(a\): other per-kWh charges ($/kWh)
times the electricity used \(E\),
③
and add the
\(B\): customer charge ($)
④
to get the
\(C\): total bill ($)
, and then
⑤
divide the
\(C\): total bill ($)
by the electricity used \(E\)
⑥
to get the
\(\bar{u}\): effective rate ($/kWh)
Quick example
With an energy charge of $162 (the example in formula 2), other per-kWh charges of $0.03/kWh, 1,200 kWh used and a customer charge of $12, the total bill and the effective rate are
\(C\): total bill ($)
\(=\)
energy charge ($162)
\(+\)
other charges ($0.03/kWh)
\(\times\)
usage (1,200 kWh)
\(+\)
customer charge ($12)
\(162 + 0.03 \times 1200 + 12 = 162 + 36 + 12 = 210\)
\(\bar{u} = 210 \div 1200 = 0.175\)
Key idea
The effective rate tells you what you really pay per kWh in the end. You get it just by dividing the total bill by the kWh used. With tiered rates, the effective rate goes up as usage grows, because a larger share of the kWh falls into the higher tiers. Because of the customer charge, the effective rate is also higher when usage is small (the fixed fee is spread over fewer kWh).
This number is handy for comparing plans and for a rough estimate of how much you save by using less. For an accurate estimate of savings, note that the kWh you cut come off the top tier first (in the example, $0.16 + $0.03 = $0.19 per kWh). Use that tier's price, not the effective rate ($0.175), for an exact answer.
kWh a budget allows (working backward)
Standard notation
(the usual math form)
\(E\)
\(=\)
\((\)
\(P\)
\(-\)
\(B\)
\()\)
\(\div\)
\((\)
\(u\)
\(+\)
\(a\)
\()\)
In words
(symbols replaced with words)
⑤
\(E\): kWh you can use
\(=\)
\((\)
①
\(P\): budget ($)
\(-\)
②
\(B\): customer charge ($)
\()\)
\(\div\)
\((\)
③
\(u\): rate ($/kWh)
\(+\)
④
\(a\): other per-kWh charges ($/kWh)
\()\)
The formula in words
①
From the
\(P\): budget ($)
②
subtract the
\(B\): customer charge ($)
to get the money left for usage,
③
then divide it by what you really pay per kWh, which is the
\(u\): rate ($/kWh)
④
plus the
\(a\): other per-kWh charges ($/kWh)
⑤
and you get the
\(E\): kWh you can use
Quick example
With a budget of $165, a customer charge of $12, a rate of $0.14/kWh and other per-kWh charges of $0.03/kWh, the kWh you can use within the budget are
\(E\): kWh you can use
\(=\)
\((\)
budget ($165)
\(-\)
customer charge ($12)
\()\)
\(\div\)
\((\)
rate ($0.14/kWh)
\(+\)
other charges ($0.03/kWh)
\()\)
\((165 - 12) \div (0.14 + 0.03) = 153 \div 0.17 = 900\)
Key idea
Working backward is just formula 1 solved for \(E\). It takes two steps: subtract the fixed cost (the customer charge) first, then divide what is left by the real price per kWh. This matches formula 1: 900 kWh gave a bill of $165.
With tiered rates, one division is not enough. Take the budget minus the customer charge and spend it from the cheapest tier upward, "tier width × that tier's price per kWh (rate + other charges)" at a time. For example, with $198 left (a budget of $210 and a customer charge of $12), other charges of $0.03/kWh and tiers of "first 500 kWh at $0.12, up to 1,000 kWh at $0.14, over 1,000 kWh at $0.16":
Tier 1: spend \(500 \times (0.12 + 0.03) = 75\) dollars, leaving \(198 - 75 = 123\) dollars
Tier 2: spend \(500 \times (0.14 + 0.03) = 85\) dollars, leaving \(123 - 85 = 38\) dollars
Tier 3: the remaining \(38 \div (0.16 + 0.03) = 200\) kWh
So the kWh you can use are \(500 + 500 + 200 = 1200\) (this matches the $210 bill in formula 3). If the money runs out in a middle tier, add "money left ÷ that tier's price" and stop there. This calculator does these steps for you.
An electric bill is made of a fixed customer charge plus a part that grows with usage. With a flat rate, the bill is "kWh × (rate + other per-kWh charges) + customer charge". With tiered rates, stack the kWh from the cheapest tier, add up "kWh in each tier × that tier's rate", then add the other per-kWh charges × kWh and the customer charge. The total divided by the kWh is the effective rate, what you really pay per kWh, and following the same formula backward gives the kWh a budget allows.
Symbols and terms
Symbols
| \(E\) | Electricity used (energy). The total electricity used that month, in kWh (kilowatt-hours). From the word "energy". Your bill may call it "usage" or "kWh used". |
| \(u\) | Rate. The price of 1 kWh ($/kWh). From "unit price". |
| \(a\) | Other per-kWh charges ($/kWh). The total of charges added for each kWh used, such as a fuel adjustment charge, delivery charges and riders. From the word "addition". It can be negative (a credit). |
| \(B\) | Customer charge ($/month). A fixed monthly fee you pay no matter how much you use. From "basic charge". |
| \(C\) | Total bill ($). From the word "cost". |
| \(L_1,\ L_2\) | The Tier 1 and Tier 2 limits (kWh) of a tiered rate. From the word "limit". The small number at the lower right (a subscript) shows which tier. For "first 500 kWh", \(L_1 = 500\). |
| \(E_1,\ E_2,\ E_3\) | The kWh in each tier. When usage \(E\) is stacked from the cheapest tier, this is the amount that falls in each tier. \(E_1 + E_2 + E_3 = E\). |
| \(u_1,\ u_2,\ u_3\) | The rate of each tier ($/kWh). In most tiered plans, higher tiers cost more. |
| \(F\) | Energy charge ($). The part of the bill figured with the tier rates. From "fee". |
| \(\bar{u}\) | Effective rate ($/kWh). The total bill divided by the kWh used, or what you really pay per kWh. The bar over the letter marks an averaged value, just as the mean is written \(\bar{x}\) in statistics. |
| \(P\) | Budget ($). The most you want to pay for electricity. B is already used for the customer charge, so this page uses P, from "plan", for the budget. |
| \(\min(E,\ L_1)\) | The smaller of \(E\) and \(L_1\). Short for "minimum". It writes "the limit if usage is over it, otherwise the usage itself" as one expression. |
Terms
| kWh (kilowatt-hour) | The unit of energy, or the total amount of electricity used. Using 1 kW (1000 W) for 1 hour uses 1 kWh. Electric bills are based on kWh, such as "usage 900 kWh". |
| Electric bill | The monthly statement from your utility. It shows the kWh used, the amount due and the rates and charges. Many utilities also show it on their website or app. |
| Customer charge | A fixed monthly fee you pay even if you use no electricity. It is also called a basic service charge or a base charge. Some plans have none. |
| Energy charge | The charge based on how many kWh you use, figured as rate × kWh. With tiered rates, it is figured for each tier and added up. |
| Tiered rate | A rate that splits usage into tiers, such as "first 500 kWh", "up to 1,000 kWh" and "more than that", with a different price for each tier. When the price goes up with each tier, it is also called an inclining block rate. The more you use, the more kWh fall into the pricier tiers, so saving energy also lowers your cost per kWh. |
| Flat rate | A rate where every kWh costs the same no matter how much you use. The bill is simply "kWh × rate + customer charge". |
| Effective rate | The total bill divided by the kWh used, or what you really pay per kWh. It is an average that includes the customer charge, the tiers and the other charges, and it is used to compare plans and roughly estimate savings. |
| Fuel adjustment charge | A charge (or credit) per kWh that passes changes in the cost of power plant fuel, such as natural gas and coal, on to customers. It is updated from time to time and may be called a fuel cost adjustment or a power cost adjustment. Check your bill for the name and amount. |
| Delivery charge | The charge for bringing electricity to your home over the power lines, often split into transmission and distribution charges. In states where you can choose your electricity supplier, the bill shows the supply charge and the delivery charge separately. Many delivery charges are set per kWh. |
| Rider | An extra line item on a bill, approved by the state utility commission, that recovers a specific cost, such as energy efficiency programs or storm recovery. Many riders are charged per kWh. |
| Progressive pricing | A system where a higher rate applies only to the part above each threshold as the amount grows. Tiered electricity rates and federal income tax brackets both work this way. Not every unit is charged at the higher rate, which is the key point. |
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) |
|
| Unit rates (Grade 6) |
|
| Expressions and solving equations (Grades 7 to 8) |
|
| Graphs of linear functions (Grade 8) |
|
| Power and energy (middle school physical science) |
|
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 the bill with a flat rate
| Electricity used (kWh) | 900 |
| Rate ($/kWh) | 0.14 |
| Other per-kWh charges ($/kWh) | 0.03 |
| Customer charge ($) | 12 |
| Total bill ($) | =B1*(B2+B3)+B4 |
Table for the energy charge with tiered rates
| Electricity used (kWh) | 1200 |
| Tier 1 limit (kWh) | 500 |
| Tier 1 rate ($/kWh) | 0.12 |
| Tier 2 limit (kWh) | 1000 |
| Tier 2 rate ($/kWh) | 0.14 |
| Tier 3 rate ($/kWh) | 0.16 |
| kWh in Tier 1 | =MIN(B1,B2) |
| kWh in Tier 2 | =MAX(MIN(B1,B4)-B2,0) |
| kWh in Tier 3 | =MAX(B1-B4,0) |
| Energy charge ($) | =B7*B3+B8*B5+B9*B6 |
Table for the total bill and effective rate
| Energy charge ($) | 162 |
| Other per-kWh charges ($/kWh) | 0.03 |
| Electricity used (kWh) | 1200 |
| Customer charge ($) | 12 |
| Total bill ($) | =B1+B2*B3+B4 |
| Effective rate ($/kWh) | =B5/B3 |
Table for the kWh a budget allows
| Budget ($) | 165 |
| Customer charge ($) | 12 |
| Rate ($/kWh) | 0.14 |
| Other per-kWh charges ($/kWh) | 0.03 |
| kWh you can use | =(B1-B2)/(B3+B4) |
After you paste it, the upper cells in column B are the inputs and the green formula cells show the results automatically.
The first table is a flat-rate example, and B5 shows 165 ($). The second table is a tiered example. It uses MIN (the smaller value) and MAX (the larger value) to find the kWh in each tier (500, 500 and 200 in B7 to B9), and B10 shows an energy charge of 162 ($).
The third table adds the other per-kWh charges and the customer charge to that energy charge. B5 shows 210 ($) and B6 shows an effective rate of 0.175 ($/kWh). The fourth table works backward, and B5 shows 900 (kWh). Just change the numbers in column B to your own plan's values.
The first table is a flat-rate example, and B5 shows 165 ($). The second table is a tiered example. It uses MIN (the smaller value) and MAX (the larger value) to find the kWh in each tier (500, 500 and 200 in B7 to B9), and B10 shows an energy charge of 162 ($).
The third table adds the other per-kWh charges and the customer charge to that energy charge. B5 shows 210 ($) and B6 shows an effective rate of 0.175 ($/kWh). The fourth table works backward, and B5 shows 900 (kWh). Just change the numbers in column B to your own plan's values.
How to calculate it in Google Sheets
Copy the whole table below and paste it into cell A1 in Google Sheets. It works as is.
Table for the bill with a flat rate
| Electricity used (kWh) | 900 |
| Rate ($/kWh) | 0.14 |
| Other per-kWh charges ($/kWh) | 0.03 |
| Customer charge ($) | 12 |
| Total bill ($) | =B1*(B2+B3)+B4 |
Table for the energy charge with tiered rates
| Electricity used (kWh) | 1200 |
| Tier 1 limit (kWh) | 500 |
| Tier 1 rate ($/kWh) | 0.12 |
| Tier 2 limit (kWh) | 1000 |
| Tier 2 rate ($/kWh) | 0.14 |
| Tier 3 rate ($/kWh) | 0.16 |
| kWh in Tier 1 | =MIN(B1,B2) |
| kWh in Tier 2 | =MAX(MIN(B1,B4)-B2,0) |
| kWh in Tier 3 | =MAX(B1-B4,0) |
| Energy charge ($) | =B7*B3+B8*B5+B9*B6 |
Table for the total bill and effective rate
| Energy charge ($) | 162 |
| Other per-kWh charges ($/kWh) | 0.03 |
| Electricity used (kWh) | 1200 |
| Customer charge ($) | 12 |
| Total bill ($) | =B1+B2*B3+B4 |
| Effective rate ($/kWh) | =B5/B3 |
Table for the kWh a budget allows
| Budget ($) | 165 |
| Customer charge ($) | 12 |
| Rate ($/kWh) | 0.14 |
| Other per-kWh charges ($/kWh) | 0.03 |
| kWh you can use | =(B1-B2)/(B3+B4) |
The formulas use only basic arithmetic and the MIN and MAX functions, 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 plan's values.
How to calculate it in Python
kwh = 1200 # Electricity used (kWh)
base_fee = 12 # Customer charge ($/month). 0 if none
extra_per_kwh = 0.03 # Other per-kWh charges ($/kWh). 0 if none
# Tiered rate: (limit in kWh, rate) from the cheapest tier. The last tier has limit None (no limit)
# For a flat rate, write just one tier, such as [(None, 0.14)]
tiers = [(500, 0.12), (1000, 0.14), (None, 0.16)]
# kWh and charge for each tier (stack the usage from the cheapest tier)
energy_charge = 0
previous_limit = 0
for limit, unit_price in tiers:
if limit is None:
part = max(kwh - previous_limit, 0)
else:
part = max(min(kwh, limit) - previous_limit, 0)
previous_limit = limit
energy_charge += part * unit_price
print(f"{part:.2f} kWh x ${unit_price}/kWh = ${part * unit_price:.2f}")
total = energy_charge + extra_per_kwh * kwh + base_fee
print(f"Energy charge ${energy_charge:.2f} / other charges ${extra_per_kwh * kwh:.2f} / customer charge ${base_fee}")
print(f"Total bill ${total:.2f} / effective rate ${total / kwh:.4f}/kWh")
# Working backward: kWh a budget allows (fill the tiers in order)
budget = 210
remaining = budget - base_fee
available_kwh = 0
previous_limit = 0
for limit, unit_price in tiers:
price_with_extra = unit_price + extra_per_kwh
if limit is None:
available_kwh += remaining / price_with_extra
break
cost_to_fill = (limit - previous_limit) * price_with_extra
if remaining <= cost_to_fill:
available_kwh += remaining / price_with_extra
break
available_kwh += limit - previous_limit
remaining -= cost_to_fill
previous_limit = limit
print(f"kWh you can use with a ${budget} budget: {available_kwh:.2f} kWh")
It runs with the standard library only. Change the kWh, customer charge and other charges at the top, and the list of tiers, to your own plan's values and run it. For a flat-rate plan, make tiers a single tier, "[(None, rate)]". The second half works backward; change budget to see the kWh you can use.
How to write it in LaTeX and other math languages (copy and paste)
Bill with a flat rate
C = E × (u + a) + B
C = E \times (u + a) + B
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>C</mi>
<mo>=</mo>
<mi>E</mi>
<mo>×</mo>
<mo>(</mo>
<mi>u</mi>
<mo>+</mo>
<mi>a</mi>
<mo>)</mo>
<mo>+</mo>
<mi>B</mi>
</mrow>
</math>
C = E * (u + a) + B
cost = energy*(unitPrice + extra) + baseFee
C := E*(u + a) + B;
C = E*(u + a) + B;
C = E×(u + a) + B
Energy charge with tiered rates (sum of the tiers)
F = E₁×u₁ + E₂×u₂ + E₃×u₃
F = E_1 u_1 + E_2 u_2 + E_3 u_3
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>F</mi>
<mo>=</mo>
<msub><mi>E</mi><mn>1</mn></msub>
<msub><mi>u</mi><mn>1</mn></msub>
<mo>+</mo>
<msub><mi>E</mi><mn>2</mn></msub>
<msub><mi>u</mi><mn>2</mn></msub>
<mo>+</mo>
<msub><mi>E</mi><mn>3</mn></msub>
<msub><mi>u</mi><mn>3</mn></msub>
</mrow>
</math>
F = E_1 u_1 + E_2 u_2 + E_3 u_3
energyCharge = e1*u1 + e2*u2 + e3*u3
F := E1*u1 + E2*u2 + E3*u3;
F = E1*u1 + E2*u2 + E3*u3;
F = E_1 u_1 + E_2 u_2 + E_3 u_3
Total bill and effective rate
C = F + a × E + B, ū = C ÷ E
C = F + aE + B, \quad \bar{u} = \frac{C}{E}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>C</mi>
<mo>=</mo>
<mi>F</mi>
<mo>+</mo>
<mi>a</mi>
<mi>E</mi>
<mo>+</mo>
<mi>B</mi>
<mo>,</mo>
<mspace width="1em"/>
<mover><mi>u</mi><mo>¯</mo></mover>
<mo>=</mo>
<mfrac><mi>C</mi><mi>E</mi></mfrac>
</mrow>
</math>
C = F + a E + B, bar u = C / E
total = energyCharge + extra*energy + baseFee; effectivePrice = total/energy
C := F + a*E + B; ubar := C/E;
C = F + a*E + B; u_bar = C/E;
C = F + aE + B, u̅ = C/E
kWh a budget allows (working backward)
E = (P − B) ÷ (u + a)
E = \frac{P - B}{u + a}
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>E</mi>
<mo>=</mo>
<mfrac>
<mrow><mi>P</mi><mo>−</mo><mi>B</mi></mrow>
<mrow><mi>u</mi><mo>+</mo><mi>a</mi></mrow>
</mfrac>
</mrow>
</math>
E = (P - B) / (u + a)
energy = (budget - baseFee)/(unitPrice + extra)
E := (P - B)/(u + a);
E = (P - B)/(u + a);
E = (P − B)/(u + a)
How to have ChatGPT do the calculation
You are an electric bill 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). The electricity used is 1,200 kWh. The plan has tiered rates: $0.12/kWh for the first 500 kWh, $0.14/kWh above 500 kWh up to 1,000 kWh, and $0.16/kWh above 1,000 kWh. The customer charge is $12 a month, and other per-kWh charges (such as a fuel adjustment charge) total $0.03/kWh. For the tiered rate, stack the usage from the cheapest tier and add up "kWh in each tier × that tier's rate" to get the energy charge. Then add "other charges × kWh" and the customer charge to get the total. Find each of the following. 1. The kWh and charge ($) in each tier 2. The energy charge, the total of the other charges, the customer charge and the total bill ($) 3. The effective rate (total ÷ kWh, in $/kWh, to 4 decimal places) 4. With the same plan, how many kWh you can use to keep the bill under $180 (spend the budget minus the customer charge from the cheapest tier upward) Show the formulas you used and the numbers from the output.
How to Use
-
1Enter your numbersType the numbers you want to calculate with into the input fields
-
2CalculatePress the "Calculate" button
-
3Check the resultThe result appears on the spot. The same page also explains the idea behind the calculation and the formula
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