Calculating solar panel cost comes down to one formula: system size in watts multiplied by the installed price per watt, plus extras, minus incentives. This guide walks through five steps, from finding your annual electricity use to sizing the system with NREL’s PVWatts tool. It includes a worked example using the 2026 US benchmark of $3.36 per watt, a cost table for 4 kW to 12 kW systems, and a breakdown of what the price actually pays for. It covers batteries, roof work, and the end of the federal homeowner tax credit, so you can check any installer’s quote.