Under variable costing, only variable production costs are treated as product costs. Under variable costing, variable selling and administrative costs are included in product costs. Absorption costing treats all manufacturing costs as product costs. In the preparation of financial statements using variable costing, fixed manufacturing overhead is treated as a period cost. Absorption costing treats fixed manufacturing overhead as a period cost. When the number of units in work in process and finished goods inventories increase, absorption costing net operating income will typically be greater than variable costing net operating income. Net operating income computed using absorption costing will always be greater than net operating income computed using variable costing. When production exceeds sales for the period, absorption costing net operating income will exceed variable costing net operating income. Absorption costing net operating income is closer to the net cash flow of a period than is variable costing net operating income. Variable costing is not permitted for income tax purposes, but it is widely accepted for external financial reports. Variable costing is better suited to cost-volume-profit calculations than absorption costing