Understanding your new bill
Working from dollars instead of kWh
Not everyone has their kWh usage handy, but almost everyone knows their monthly bill amount. A $150 monthly bill with an 85% offset saves about $127.50 a month, leaving a new bill of roughly $22.50. This shortcut skips the kWh math entirely and works directly from what's on your statement. The production figure behind this estimate comes from the monthly kwh output estimator, which models output for your location and roof.
Why your bill rarely hits exactly $0
Most utilities charge a minimum monthly service or connection fee that applies no matter how much solar you produce, often somewhere between $10 and $25. Even a system sized to fully offset your usage typically still shows a small residual charge each month. The zero dollar bill calculator looks specifically at what it takes to get as close to $0 as realistically possible. For the official overview, the US Department of Energy's homeowner's guide to going solar covers buying, leasing, and system sizing.
Where the offset percentage comes from
Installers calculate offset based on your system's expected production against your historical usage. If you want to estimate it yourself rather than rely on a quote, the bill offset percentage calculator builds that figure from your system size and usage directly. The system size by monthly kwh usage is the quickest way to check whether the system size behind this estimate fits your roof and usage.
Turning this into a full savings picture
This tool gives you a snapshot based on your current bill. For a version built from usage and utility rate instead, try the solar savings calculator, or see the annual bill reduction estimator for a yearly total in one step. The US Energy Information Administration's electricity data show how retail rates have moved, which is the starting point for any savings estimate.