Cost Formulas

How to Calculate Standard Cost Variances, Overhead Absorption, and WIP Value

The core cost-accounting formulas worked end to end: variance decomposition, overhead absorption, and WIP value, with real inputs and where each one comes from.

Every standard-cost calculation starts from one identity: total variance equals actual cost minus standard cost. Say a machined part carries a $40.00 standard and 8,000 good units ran at a $3.20 per-unit overrun on 100% of output, plus a $1,200 period true-up. The Standard Cost Variance formula gives 8,000 x $3.20 x 100% + $1,200 = $26,800 unfavorable, or $3.35 per unit once the fixed adder spreads across the run. The units come from confirmed good output on the production report, the per-unit gap from actual ledger cost minus the frozen standard, and the adjustment from any reclass booked to variance at close.

Material variance splits into price and usage, and you never blend them. Set the standard first: at a 12 units per hour draw over an 8 hour run, expected consumption is 96 units, and at a $3.50 per unit standard the Material Variance baseline run cost is $336. Now compare. Usage variance is (actual quantity minus 96) times the $3.50 standard price, so drawing 104 units costs (104 - 96) x $3.50 = $28.00 unfavorable. Price variance is (actual price minus $3.50) times actual quantity. Hold price at standard when you compute usage, and hold quantity at standard when you compute price, or you double-count the interaction term.

Labor variance follows the same two-part logic on hours and rate. Build the standard from a time study: 120 units at 12 units per minute is 10.0 base hours, and a 10% allowance for setup and handling lifts it to 11.0 standard hours per the Labor Variance method. Efficiency variance is (actual hours minus 11.0) times the standard wage. At a $28.00 per hour rate, clocking 12.5 hours yields (12.5 - 11.0) x $28.00 = $42.00 unfavorable. Rate variance is (actual wage minus $28.00) times actual hours. Standard hours earned only credit good units, so scrapped pieces earn nothing and inflate the efficiency gap correctly.

Overhead absorption converts a budgeted indirect pool into a rate the product carries. First derive the rate: budgeted overhead divided by the absorption base. A cell budgeting $260,000 over 4,000 machine hours yields $65.00 per machine hour. Then apply it with Overhead Absorption: 4,000 hours x $65.00 x 95% utilization + a $10,000 fixed facility floor totals $257,000 absorbed, or $64.25 per machine hour all in. Absorb at practical capacity near 80% to 95%, not theoretical 100%, so idle-capacity cost is expensed to the period rather than buried in inventory value where it silently overstates the balance sheet.

The gap between absorbed and actual overhead is the volume and spending variance you must clear each month. If the cell above absorbed $257,000 but actual overhead landed at $271,000, you are $14,000 under-absorbed, a debit that hits the income statement. Split it: the spending piece is actual overhead minus budgeted overhead at actual hours, and the volume piece is the fixed rate times the hours you missed versus plan. Miss 300 of the 4,000 planned hours at, say, a $22.00 fixed component and volume variance alone is 300 x $22.00 = $6,600 under-absorbed before any spending overrun.

Cost center rates make product costing accurate when cells differ. Rather than one plant-wide rate, the Cost Center Rate and Burden Rate tools build a rate per department: a labor-intensive assembly cell might carry $38.00 per labor hour while a CNC cell carries $65.00 per machine hour. Pick the base that drives the cost. Use machine hours where equipment time dominates, such as injection molding, and labor hours where manual content dominates. A single blended rate cross-subsidizes, making the capital-heavy part look cheap and the labor-heavy part look expensive by 10% to 30% depending on the mix.

WIP valuation rolls these pieces into a balance-sheet number. For each stage, value material issued plus labor applied plus absorbed overhead, scaled by percent complete. A batch that is 100% material complete and 60% through conversion carries full material plus 60% of the standard labor and overhead. If material is $336, standard conversion is $500, and the batch is 60% converted, WIP value per the WIP Valuation and Inventory Valuation Impact logic is $336 + 0.60 x $500 = $636. Getting conversion percentage wrong by 10 points on a large batch swings reported inventory by thousands, so tie the percentage to routing operations completed, not a floor estimate.

Chain these correctly and the numbers reconcile. Total variance from Actual vs Standard Cost should equal the sum of your material price, material usage, labor rate, labor efficiency, and overhead volume and spending variances. If it does not tie, you have a unit error, a sign flip, or a missing pool. On the $22,175 confidence-weighted gap from a 5,000-unit reconciliation at a $4.75 per-unit gap and 90% confidence plus an $800 allocation delta, every dollar should trace to a named cause. A variance you cannot decompose is not a variance, it is a data problem to fix before close.

Published 2026-07-01.