An offset percent answers the question every solar customer asks: how much of my power does the system actually cover? Divide the kWh produced by the kWh used, month by month.
900 kWh produced against 1,000 kWh used is a 90% offset — the grid covers the last tenth.
The example
Three months, each with kWh produced and kWh used.
| A | B | C | D | |
|---|---|---|---|---|
| 1 | Month | Produced kWh | Used kWh | Offset % |
| 2 | May | 800 | 1,000 | 80.0% |
| 3 | June | 900 | 1,000 | 90.0% |
| 4 | July | 1,150 | 1,250 | 92.0% |
The formula
One division turns two meter reads into an offset:
How it works
Offset is production as a share of usage:
B2is the kWh the array produced that month, from the inverter or monitoring app.C2is the kWh the home used, from the utility bill.- Dividing and formatting as a percent shows the share solar covered.
Track it monthly — a system can hit 110% in June and 60% in December and still net to full annual offset.
Try it: interactive demo
Enter the kWh produced and the kWh used.
Variations
Cap the display at 100%
Stop the reading at full offset for a cleaner dashboard.
Annual offset
Net a whole year with total production over total usage.
Pitfalls & errors
Compare the same billing period on both meters; a production month that does not line up with the usage month skews the offset.
Judge offset over a year, not a month — net metering banks summer surplus to cover short winter days.
Practice workbook
Frequently asked questions
What does 100% offset mean?
Why track it monthly?
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