变动成本（Variable costs）是经济学的名词，与固定成本相对应，指在生产过程中可被增加或减少的生产因素（Production Factor）回报或称转移收入／转移收益（Transfer Earnings），例如劳工、工具的成本。换句话说，是指会随着产量或业务量变化而变化的成本，即是边际成本的总和。可变成本的相反是固定成本（Fixed Cost）。经常性成本即由变动成本和固定成本二者组成。

变动成本中又可分为直接成本和间接成本。

Variable costs are costs that change in proportion to the good or service that a business produces. Variable costs are also the sum of marginal costs over all units produced. They can also be considered normal costs. Fixed costs and variable costs make up the two components of total cost. Direct costs, however, are costs that can easily be associated with a particular cost object. However, not all variable costs are direct costs. For example, variable manufacturing overhead costs are variable costs that are indirect costs, not direct costs. Variable costs are sometimes called unit-level costs as they vary with the number of units produced.