In a standard cost system, accountants apply the manufacturing overhead to the goods produced using a standard overhead rate. They set the rate prior to the start of the period by dividing the budgeted manufacturing overhead cost by a standard level of output or activity. Total budgeted manufacturing overhead varies at different levels of standard output, but since some overhead costs are fixed, total budgeted manufacturing overhead does not vary in direct proportion with output.

Managers use a flexible budget to isolate overhead variances and to set the standard overhead rate. Flexible budgets show the budgeted amount of manufacturing overhead for various levels of output.

Look at Beta Company's flexible budget below. Note that Beta's flexible budget shows the variable and fixed manufacturing overhead costs expected to be incurred at three levels of activity: 9,000 units, 10,000 units, and 11,000 units. For product costing purposes, Beta must estimate the expected level of activity in advance and set a rate based on that level. The level chosen is called the standard volume of output. This standard volume of output (or activity) may be expressed in terms of any of the activity bases used in setting standard overhead rates. These activity bases include percentage of capacity, units of output machine-hours, and direct labor-hours, among others.   Machine-hours are budgeted at 2 machine-hours per product.  In our example, standard volume is assumed to be 10,000 units produced. Management expects to use 20,000 machine-hours of services.  These will be used as our budgeted amounts.

 BetaCompany Flexible manuf.  overhead budget Machine-hours 18,000 20,000 22,000 Units of output 9,000 10,000 11,000 Variable overhead: Indirect materials $7,200$8,000 $8,800 Power 9,000 10,000 11,000 Royalties 1,800 2,000 2,200 Other 18,000 20,000 22,000 Total variable overhead$36,000 $40,000$44,000 Fixed overhead: Insurance $4,000$4,000 $4,000 Property taxes 6,000 6,000 6,000 Depreciation 20,000 20,000 20,000 Other 30,000 30,000 30,000 Total fixed overhead$60,000 $60,000$60,000 Total Overhead (variable + fixed ) $96,000$100,000 $104,000 Standard overhead rate ($100,000/20,000 hours) $5 Assume that Beta applies manufacturing overhead using a rate based on machine-hours. According to the flexible manufacturing overhead budget, the expected manufacturing overhead cost at the standard volume (20,000 machine-hours) is$ 100,000, so the standard overhead rate is $5 per machine-hour ($100,000/20,000 machine-hours).

Knowing the separate rates for variable and fixed overhead is useful for decision making.  We will be using the company's expected volume of 10,000 units.  The variable overhead rate is $2 per machine hour ($ 40,000 variable OH/20,000 hours), and the fixed overhead rate is $3 per hour ($ 60,000/20,000 hours). If the expected volume had been 18,000 machine-hours, the standard overhead rate would have been $5.33 ($96,000/18,000 hours). If the standard volume had been 22,000 machine-hours, the standard overhead rate would have been $4.73 ($104,000/22,000 hours).

Note that the difference in rates is due solely to dividing fixed overhead by a different number of machine-hours. That is, the variable overhead cost per unit stays constant ($2 per machine-hour) regardless of the number of units expected to be produced, and only the fixed overhead cost per unit changes. Since fixed overhead does not change per unit, we will separate the fixed and variable overhead for variance analysis. Continuing with the Beta Company illustration, assume that the company incurred$ 108,000 of actual manufacturing overhead costs ($46,000 in variable OH and$62,000 in fixed OH) in a period during which 11,000 units of product were produced. The actual costs would be debited to Manufacturing Overhead and credited to a variety of accounts such as Accounts Payable, Accumulated Depreciation, Prepaid Insurance, Property Taxes Payable, and so on. According to the flexible budget, the standard number of machine-hours allowed for 11,000 units of production is 22,000 hours. Therefore, $110,000 of manufacturing overhead is applied to production ($ 5 per machine-hour times 22,000 hours) by debiting Work in Process Inventory and crediting Manufacturing Overhead for $110,000. These show that manufacturing overhead has been overapplied to production by the$ 2,000 ($110,000 applied OH -$108,000 actual OH). Because of its fixed component, manufacturing overhead tends to be over applied when actual production is greater than standard production.  Now, we will separate the variable and fixed components for analysis.

Although various complex computations can be made for overhead variances, we use a simple approach in this text. In this approach, known as the two-variance approach to variable overhead variances, we calculate only two variances—a variable overhead spending variance and a variable overhead efficiency variance.

Variable Overhead Spending Variance The variable overhead spending variance shows in one amount how economically overhead services were purchased and how efficiently they were used. This overhead spending variance is similar to a price variance for materials or labor. We compare the Variable OH rate for budget and actual using the actual amount of our variable overhead base (machine-hours, direct labor dollars, direct labor hours, etc.)

Variable OH Spending Variance = (Actual Variable OH per base - Std Variable OH per base) x Actual OH base

OR

Variable OH Spending Variance = (Actual OH base x Actual Variable OH per base) - (Actual OH base x Std Variable OH per base)

For Beta Company, overhead is applied based on machine hours.   The Variable OH rate per machine hour is $2 (calculated above) and actual variable overhead was$46,000 for 22,000 actual machine hours giving an actual rate of $2.0909 rounded ($46,000 / 22,000 actual machine hours).  We can calculate the variable OH spending variance using either of these two methods below:

Variable OH Spending Variance = (Actual Variable OH per base - Std Variable OH per base) x Actual OH base

= ($2.0909 per machine hour -$2.00 per machine hour) x 22,000 actual machine hours

= $0.0909 x 22,000 machine hours =$2,000 (rounded) Unfavorable

OR

Variable OH Spending Variance = (Actual OH base x Actual Variable OH per base) - (Actual OH base x Std Variable OH per base)

=  $46,000 actual variable OH - (22,000 actual machine hours x$2 standard OH per machine hour)

= $46,000 - 44,000 =$2,000 unfavorable

The variance is unfavorable because actual variable overhead costs were $46,000, while according to the flexible budget for 11,000 units, they should have been$44,000 meaning Beta spent more on variable overhead than they had planned.Variable Overhead Efficiency Variance The variable efficiency overhead variance is caused by producing at a level other than that used in setting the standard overhead application rate. The variable OH efficiency variance shows whether plant assets produced more or fewer units than expected.

Variable OH Efficiency Variance = (Actual OH base - Std OH base) x Standard Variable OH per base

OR

Variable OH Efficiency Variance = (Actual OH base x Std Variable OH per base) - (Std OH base x Std Variable OH per base)

For Beta Company, the Variable OH rate per machine hour is $2 (calculated above) and actual variable overhead was$46,000 for 22,000 actual machine hours.  Management expected to use 20,000 hours for 10,000 units produced.  We can calculate the variable OH spending variance using either of these two methods below:

Variable OH Efficiency Variance = (Actual OH base - Std OH base) x Standard Variable OH per base

= (22,000 actual machine hours - 20,000 standard machine hours ) x $2 per machine hour = 2,000 machine hours x$2 per machine hour

= $4,000 unfavorable OR Variable OH Efficiency Variance = (Actual OH base x Std Variable OH per base) - (Std OH base x Std Variable OH per base) = (22,000 actual hours x$2 per machine hour) - (20,000 standard hours x $2 per machine hour) =$44,000 - 40,000

= $4,000 unfavorable The efficiency variance is unfavorable because we used more machine hours than we had budgeted. Of course, this is because we produced 11,000 units when the budget planned for 10,000 units. Fixed Overhead Variance Because fixed overhead is not constant on a per unit basis, any deviation from planned production causes the overhead application rate to be incorrect. We can calculate a fixed overhead variance by comparing: Fixed Overhead variance = Actual fixed overhead - Budgeted fixed overhead In the Beta Company illustration, the budgeted fixed overhead was$60,000 (notice the level of production does not matter since fixed costs remain the same regardless of volume) and the actual fixed costs were $62,000. Fixed Overhead variance = Actual fixed overhead - Budgeted fixed overhead =$62,000 actual fixed - $60,000 budgeted fixed =$2,000 unfavorable variance

This variance is unfavorable since we spent more on fixed costs than we had planned.

Summary of overhead variances To easily determine the accuracy of the overhead variances, Beta would compare the sum of the variances with the difference between the costs of actual manufacturing overhead and budgeted manufacturing overhead. For Beta Company, the difference between actual and budgeted overhead (budget is based on the expected level of volume of 10,000 units) was:

 Actual manufacturing overhead incurred $108,000 Budgeted overhead (at 10,000 units) 100,000 Total overhead variance (unfavorable)$ 8,000
 Variable OH Spending Variance $2,000 U Variable OH Efficiency Variance$ 4,000 U Fixed OH Variance $2,000 U Total overhead variance (2,000 U + 4,000 U + 2,000 U)$8,000 Unfavorable