Cost Accounting

Machine Depreciation in Product Cost: Straight-Line vs. Units of Production

Depreciation method changes what each routed part carries for equipment burden. This guide shows when straight-line or output-based logic gives the cleaner cost signal for quoting and margin review.

Machine depreciation becomes a product cost when it is included in the machine hour rate used to price and cost each operation in a routing. Machine hour rate = (annual depreciation + annual maintenance + annual energy + annual tooling + annual facilities burden) / planned production hours per year. If a $480,000 5-axis machining center is depreciated straight-line over 10 years with $10,000 salvage, annual depreciation is ($480,000 - $10,000) / 10 = $47,000. At 3,200 planned run hours per year and $28,000 in total other annual costs, machine hour rate = ($47,000 + $28,000) / 3,200 = $23.44 per hour. A part with a 4.5-minute cycle time on that machine carries $23.44 x (4.5/60) = $1.76 in machine burden. When a quoting tool uses this rate, depreciation is recovered proportionally to actual machine use.

Units-of-production depreciation ties annual depreciation expense to actual output rather than time. Annual depreciation = (cost - salvage) x (units produced this year / total expected lifetime units). For the same $480,000 machine with a 200,000-part expected lifetime, a year producing 18,000 parts incurs depreciation of ($480,000 - $10,000) x (18,000 / 200,000) = $42,300. A year at 24,000 parts incurs $56,400. This method loads more depreciation cost into high-volume periods and less into low-volume periods, which is a more economically accurate representation of how the asset is consumed. The trade-off is that it introduces variability into the cost base, which complicates budgeting and variance reporting if the finance team expects a stable monthly depreciation charge.

The practical quoting implication of depreciation method is largest when utilization varies significantly across product lines or time periods. Under straight-line depreciation absorbed through a fixed machine hour rate, a machine running at 50% utilization compared to the planned 80% utilization still recovers the same depreciation per part produced. The underutilization shows up as unabsorbed overhead at period end rather than in individual part costs. Under units-of-production logic, the cost per part rises when fewer parts run because annual depreciation is spread over fewer units. This is more accurate but can make quotes look uncompetitive in slow periods. Understanding this dynamic is critical when renegotiating long-term supply agreements, since the customer is effectively bearing some of the volume risk if the contract price embeds a units-of-production rate.

Capital justification for new equipment almost always requires a cost-per-part projection that specifies which depreciation method will be used and what utilization assumption underlies the calculation. A $1.2 million investment justified at 85% utilization produces a very different machine hour rate than at 65% utilization. The justification rate = ($1.2M / 10-year life) / (4,000 hr/yr x utilization). At 85%: $120,000 / 3,400 = $35.29/hr. At 65%: $120,000 / 2,600 = $46.15/hr. A 20-percentage-point utilization miss raises the depreciation component of machine hour rate by 31%. Capital requests that present only the 85% scenario are the ones that produce budget surprises when the machine takes 18 months to ramp. Sensitivity analysis around utilization should be a standard section in every capital justification model.

Full absorption costing requires that depreciation be allocated to inventory and cost of goods sold, which means depreciation method affects reported margins on unsold inventory. In periods when inventory builds, more fixed overhead (including depreciation) is capitalized into inventory value under full absorption, smoothing reported profit. In periods when inventory is drawn down, that previously capitalized depreciation flows through to COGS, suppressing margins. For operations with seasonal production patterns or significant build-ahead inventory, understanding the absorption effect of depreciation method prevents incorrect conclusions from monthly P&L reviews. The best practice is to run a machine hour rate model that shows total depreciation recovery at multiple utilization levels so operations and finance can agree in advance on how under-recovery will be reported.

Published 2026-05-28.