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Bill offset percentage calculator
See exactly what percentage of your electric bill your solar system offsets, with a plain-language category from minor to full offset.
How it works
One step to your offset percentage
Step 1
Enter your production and usage
Use figures from the solar panel calculator if you haven't worked these out yet.
Step 2
Get your offset percentage and category
The tool divides production by usage and caps the result at 100%, with a plain-language category explaining what the number means. For usage-tier examples, see the high usage home savings calculator.
Understanding bill offset percentage
How the calculation works
Offset percentage is your system's annual production divided by your annual electricity usage, capped at 100%. A 9,490 kWh system against 12,000 kWh of annual usage works out to a 79.1% offset, categorized as a majority offset, the same figure shown on the 1000 kWh a month calculator. The US Department of Energy's homeowner's guide to going solar walks through the same decision step by step.
What the categories mean
Full offset is 100% or more, near-full offset is 80% to 99%, majority offset is 50% to 79%, partial offset is 25% to 49%, and minor offset is anything below 25%. These are rough, plain-language labels rather than industry-standard terms, meant to give quick context to the raw percentage. Renters and shaded roofs have another path, and the community solar 100 percent offset calculator explains how shared solar subscriptions work.
Why the percentage caps at 100%
In terms of raw production versus usage, the ratio can exceed 100%, but the offset applied to your bill caps at that point since a utility generally won't pay you more than your bill was worth through simple offset alone. Any production beyond 100% becomes excess, subject to your utility's net metering policy, similar to the scenario covered in the low usage home savings calculator and the zero dollar bill calculator. For background on how solar power is generated, the solar explainer from the US Energy Information Administration is a solid starting point.
Offset percentage isn't the same as dollar savings
Offset percentage measures coverage relative to your own usage, not the dollar value of your savings. A small system offsetting 100% of a low bill can save less in absolute dollars than a larger system offsetting 60% of a much bigger bill, so it's worth looking at both figures together rather than optimizing for percentage alone. The system size by electric bill amount is the quickest way to check whether the system size behind this estimate fits your roof and usage.
Questions
Frequently asked
Offset percentage is your system's annual production divided by your annual electricity usage, capped at 100%. A 9,490 kWh system against 12,000 kWh of annual usage works out to a 79.1% offset, categorized as a majority offset.
Full offset is 100% or more, near-full offset is 80% to 99%, majority offset is 50% to 79%, partial offset is 25% to 49%, and minor offset is anything below 25%. These are rough, plain-language labels rather than industry-standard terms.
In terms of raw production versus usage, yes, but the offset applied to your bill caps at 100% since a utility generally won't pay you more than your bill was worth through simple offset alone. Any production beyond 100% becomes excess, subject to your utility's net metering policy.
Offset percentage measures coverage relative to your own usage, not the dollar value of your savings. A small system offsetting 100% of a low bill can save less in absolute dollars than a larger system offsetting 60% of a much bigger bill.
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