Operating expenses are the costs associated with running a business – such as payroll, inventory and supplies, marketing, utilities, and rent. These are the expenses that keep your business up and running, day-to-day. Non-operating expenses, on the other hand, are costs related to any investments or income not related to business activities. Examples include gains and losses from investing in stocks, and one-off costs like legal fees or writedowns. Whether operating or non-operating, every expense needs to be carefully managed to ensure your business stays profitable and cash flow remains positive.