Overhead costs are all the costs that do not get included on estimates. You can estimate time and equipment and salt for jobs, but you cannot estimate costs like rent or office supplies on a job-by-job basis. The prices of your bill-able work (labor, equipment, subs, materials) must be enough to recover your company's overhead. This is the first step in confident cost & pricing.
Open the Snow Overhead Calculator spreadsheet. Use last year's P&L for reference, but remember to forecast expense totals for next year.