Generator vs Utility Cost Calculator
The Generator vs Utility Cost Calculator estimates the monthly operating cost difference between producing electricity with a fuel-powered generator and buying the same amount of energy from your utility. It combines your estimated generator run time, fuel use, fuel price, and maintenance allowance, then compares that total with the cost of utility electricity.
The result can help readers of thebestgenerators.com compare running costs for a home, workshop, cabin, or other application. The default figures are illustrative assumptions, so replace them with values that reflect your generator and expected electrical load.
What the Generator vs Utility Cost Calculator does
This calculator estimates how much more or less you would spend each month to generate a specified amount of electricity instead of purchasing the same number of kilowatt-hours from your utility. Its result, labeled Monthly Cost Difference, is the estimated generator operating cost minus the estimated utility energy cost.
- A positive result means the generator is estimated to cost more per month.
- A negative result means the generator is estimated to cost less per month.
- A zero result means the two estimated energy costs are equal under the entered assumptions.
The comparison covers generator fuel and an hourly maintenance allowance. On the utility side, it uses the electricity rate you enter for each kilowatt-hour. It does not calculate the full cost of owning a generator or every charge that may appear on an electricity bill.
How to use the Generator vs Utility Cost Calculator
Enter estimates for the six fields below. The most useful comparison uses generator output and fuel consumption measured or estimated at the same expected operating load.
- Monthly electricity needed (kWh): Enter the amount of electricity you want to compare over one month. You might use a utility bill to estimate total consumption or add up the estimated consumption of selected appliances.
- Average generator output under load (kW): Enter the average electrical power the generator is expected to supply while running. Use the expected output under the relevant load, rather than assuming the generator continuously delivers its maximum rated output.
- Generator fuel consumption under load (gallons/hour): Enter the average amount of fuel the generator uses per hour at that same load. Generator documentation may provide consumption figures at different load levels.
- Fuel price ($/gallon): Enter the price you expect to pay per gallon for the generator’s fuel. Use a price in the same units as the consumption figure.
- Utility electricity rate ($/kWh): Enter the applicable marginal cost of buying an additional kilowatt-hour from your utility. This may differ from a bill’s total divided by consumption if the bill includes fixed charges or other fees.
- Generator maintenance allowance ($/hour): Enter an estimated maintenance cost for each hour the generator operates. This allowance can account for routine items such as oil, filters, and servicing.
Read the result as a monthly difference, rather than as the total cost of either option. You can change individual assumptions to see how fuel prices, operating load, or your utility rate affect the comparison.
How the Generator vs Utility Cost Calculator formula works
The calculator first estimates generator run time by dividing monthly electricity needed by average generator output. It then multiplies those hours by the combined hourly fuel and maintenance cost. Finally, it subtracts the cost of buying the same energy from the utility.
Monthly Cost Difference = (monthly electricity needed ÷ average generator output) × ((fuel consumption × fuel price) + maintenance allowance) − (monthly electricity needed × utility electricity rate)
Monthly electricity is measured in kilowatt-hours, while generator output is measured in kilowatts. Dividing kWh by kW gives estimated operating hours. Fuel consumption in gallons per hour multiplied by dollars per gallon gives a fuel cost per hour; adding the maintenance allowance gives the estimated total operating cost per hour.
Worked example using the default assumptions
Assume a household needs 300 kWh per month. The generator averages 3 kW of output and consumes 0.5 gallons per hour at that load. Also assume fuel costs $3.50 per gallon, maintenance costs $0.50 per operating hour, and utility electricity costs $0.16 per kWh. These are illustrative figures, not current price quotes.
- Estimated generator run time: 300 kWh ÷ 3 kW = 100 hours.
- Hourly fuel cost: 0.5 gallons × $3.50 = $1.75.
- Hourly fuel and maintenance cost: $1.75 + $0.50 = $2.25.
- Monthly generator operating cost: 100 hours × $2.25 = $225.00.
- Monthly utility energy cost: 300 kWh × $0.16 = $48.00.
- Monthly Cost Difference: $225.00 − $48.00 = $177.00 per month.
In this example, the positive result means the generator is estimated to cost $177.00 more per month for fuel and maintenance than buying the same 300 kWh at the assumed utility rate.
Use cases for the Generator vs Utility Cost Calculator
Planning for backup power: Estimate the running cost of supplying selected appliances during an extended outage. Enter the energy those appliances are expected to use over the period being modeled, rather than automatically using your entire normal household consumption.
Comparing a cabin or workshop: If both generator and utility power are available, compare the estimated operating cost of supplying the same monthly energy with each source. This can help you budget for the way the space is actually used.
Evaluating different loads: A generator’s output and fuel consumption can change together as the load changes. Try separate scenarios using matched output and consumption figures for each expected load to see how they affect the result.
Testing fuel-price assumptions: Change the price per gallon while keeping the other inputs consistent. This shows how a higher or lower fuel price affects the monthly operating estimate without requiring you to predict future prices.
Estimating the effect of maintenance: Compare a scenario with your planned hourly maintenance allowance against one with a different allowance. Use this as a budgeting exercise, recognizing that actual service costs may occur at intervals rather than evenly every hour.
Other factors to consider when calculating Monthly Cost Difference
The result is an operating-cost estimate, not a complete ownership comparison. It excludes the generator’s purchase price, installation, financing, and eventual replacement. It also excludes fixed utility charges and demand charges. Those costs can matter when deciding whether to buy a generator or change how you obtain electricity.
Fuel consumption and electrical output are unlikely to stay perfectly constant. Appliance cycles, partial loads, operating conditions, and generator efficiency can all change the amount of fuel used for each kilowatt-hour produced. A generator may also run at times when the connected load is low. Choose average figures that reflect your expected use and update them if you have better operating data.
The utility rate deserves attention as well. Electricity bills may include fixed fees, tiered energy prices, or time-dependent rates. For this calculator, use the rate that best represents the marginal cost per kWh for the energy you are comparing. The calculator does not separately model rate tiers, demand charges, or fixed monthly fees.
Finally, cost is only one part of a generator decision. Available capacity, reliability, fuel storage, noise, and maintenance requirements can affect whether a particular setup meets your needs. Follow the generator manufacturer’s operating instructions and applicable local requirements when planning its use.
Frequently asked questions about the Generator vs Utility Cost Calculator
What does a negative Monthly Cost Difference mean?
A negative result means the estimated generator fuel and maintenance cost is lower than the estimated utility energy cost for the same monthly kWh. It does not include generator purchase, installation, financing, or replacement costs, so it does not establish the total savings from owning a generator.
Should I enter the generator’s maximum rated output?
Enter the average output expected under load. Maximum rated output may overstate the power supplied during normal use and understate estimated run time. Match the output figure with the fuel consumption expected at the same load.
How can I estimate monthly electricity needed?
A utility bill can provide a starting point for total monthly household consumption. For selected equipment, estimate each device’s energy use in kilowatt-hours over the period and add the amounts together. Use the same energy quantity for both sides of the comparison.
Does the calculator include all generator expenses?
No. It includes fuel and the hourly maintenance allowance you enter. Purchase, installation, financing, and replacement costs are excluded, as are any other expenses not represented by those inputs.
Why might the estimate differ from my actual costs?
Actual load, fuel consumption, fuel price, maintenance expenses, and utility billing can vary from the assumptions entered. The calculation uses average generator output and consumption and a single utility rate, so it cannot capture every change during the month.