In a standard costing system, under-applied or over-applied fixed overhead is equal to the sum of the fixed overhead budget variance and the fixed overhead volume variance.

In a standard costing system, the total variance for fixed overhead indeed consists of the fixed overhead budget variance (which compares the actual fixed overhead costs to the budgeted fixed overhead costs) and the fixed overhead volume variance (which measures the difference between the budgeted fixed overhead allocated based on standard hours allowed for actual production and the actual fixed overhead incurred).