Setup amortization
Spread a defined setup cost over an explicit batch quantity while separating resource burden, supplier fees, yield, and repeated setups.
Tags: costing, manufacturing, batch-costing
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Why small batches cost more per part
A setup cost is shared by the parts produced from that setup. With an unchanged $300 setup, 100 accepted parts carry $3 each; 400 carry $0.75 each. Four separate 100-part runs still require four setups if each run needs the same preparation. These are illustrative assumptions, not shop rates.
Use this page to compare batch sizes and avoid counting a setup fee twice. Start with the complete manufacturing estimate to place setup beside material, runtime and outside services. Compare the supplier's quantity constraints before treating annual demand as one production batch.
What setup amortization means
Setup amortization, as used here, means spreading the cost of preparing a production run across the units assigned to that run. The basic relationship is setup cost per unit = setup cost / assigned unit quantity. Manufacturing cost-estimation guidance from Boothroyd Dewhurst treats setup separately from cycle time, materials, and tooling, with batch size determining its per-part burden. This is a costing allocation, not automatically the financial-statement amortization of an asset. Boothroyd Dewhurst, Machining Cost Estimator
The denominator and cost boundary are as important as the division. State which setup, operation, revision, and production lot the cost covers, and whether units mean planned starts, actual starts, or accepted output.
Define the setup being costed
In machining, setup can include preparing fixtures, loading programs, establishing offsets, and checking the first part. SolidCAM's guidance expressly separates setup-related cost per accepted part and asks whether programming, fixture preparation, offsets, first-part inspection, and prove-out are included. Different inclusions produce different rates even for the same machine. SolidCAM, Reduce CNC Machining Costs
Separate labor effort from machine downtime. The Lean Enterprise Institute's SMED guidance distinguishes internal operations requiring a stopped machine from external operations possible while it runs. Moving preparation outside downtime can release machine capacity without eliminating the preparation work. Avoid charging an hour of external preparation as an hour of stopped-machine time merely because both are called setup. Lean Enterprise Institute, Single Minute Exchange of Die
For a cost model, define:
- Setup labor hours, people involved, and the included labor burden.
- Machine-occupied hours and the included machine cost components.
- Consumables or other costs attributable to the event.
- Any separately modeled programming, fixture, or inspection costs.
- The event count and quantity receiving each event's cost.
These are model fields to establish locally, not universal charge categories. A combined shop rate may already include labor or support costs; adding them again would duplicate the same resource.
Batch-level assignment and repeat production
A setup pool can also be assigned through activity-based costing. ACCA's example divides a setup-cost pool by the number of setups, assigns setup cost to batches, and spreads each batch's cost over its units. Small batches then receive more setup cost per unit than large batches under an equal-cost-per-setup assumption. ACCA, Ken Garrett, Activity-based costing
Count the events actually required. An annual order for 400 units does not establish whether production needs one setup or four. Several operations may each need preparation; a retained fixture may reduce one task without removing the others. If setups vary substantially in effort, an equal event rate needs refinement rather than silently treating all events as identical. This is a limitation of the chosen model, not a reason to assume one setup per purchase order.
Worked example: plan, actual output, and reconciliation
Invented internal-costing example, USD. Assume one setup for one operation. One technician spends three hours, including one hour preparing off-machine and two hours while the machine is stopped. The labor rate is $40/hour. The machine rate is $60/hour and explicitly excludes that technician's labor. Setup consumables cost $60 and are excluded from both rates. No programming, reusable-fixture acquisition, tax, profit, or other support costs are included.
| Setup component | Basis | Cost |
|---|---|---|
| Technician labor | 3 hours × $40/hour | $120 |
| Machine occupation | 2 hours × $60/hour | $120 |
| Setup consumables | Separately measured | $60 |
| Total setup burden | Sum | $300 |
The planned run is 100 accepted parts, so the planned burden is $300 / 100 = $3/accepted part. Suppose the run actually starts 100 parts and produces 90 accepted parts plus 10 rejected parts. The following are alternative management views of the same $300, not additive charges:
| Denominator | Setup burden per unit | Reconciliation |
|---|---|---|
| Planned accepted output: 100 | $3.00 | 100 × $3 = $300 planned recovery |
| Actual starts: 100 | $3.00 | $270 on 90 accepted starts + $30 on 10 rejected starts |
| Actual accepted output: 90 | $3.333… | 90 × ($300/90) = $300 |
Use unrounded values for reconciliation. The accepted-output view concentrates the full burden on good units; it does not determine whether rejected-product costs may be included in financial-reporting inventory. The starts view exposes the $30 assigned to rejected units. Keep yield treatment explicit when comparing the two.
If a planned $3 standard is retained for 90 accepted parts, $270 is assigned and a $30 shortfall remains to explain. Do not erase that difference by calling the planned denominator actual output. Conversely, a quote explicitly based on a 100-part lot does not automatically change when the supplier's actual yield differs.
Batch size, invoices, and double counting
For a separate invented sensitivity, assume 400 accepted parts, no rejects, and $300 for every setup. One uninterrupted batch incurs $300/400 = $0.75/part; four batches of 100 incur $1,200/400 = $3/part. Their difference is three additional setup events costing $900. This assumes unchanged event cost and no inventory, scheduling, or delivery effects. It does not establish an optimal batch size.
A quoted setup fee is a price term, while the $300 example is a modeled resource burden. If a fictional supplier instead quotes a $500 setup fee plus $20 per part for 100 parts, the invoice is $500 + $2,000 = $2,500, or $25/part for comparison. Adding another $5/part setup allocation to that same $2,500 would double count the fee. Reconcile either separate fee plus recurring unit price, or an explicitly inclusive equivalent unit price.
Nor does reducing an allocated setup burden prove a cash saving. ACCA's relevant-cost guidance distinguishes changed future cash flows from reallocation of existing fixed costs. Released machine or salaried labor capacity needs a separate assessment of alternative use, avoided overtime, or spending changes. ACCA, Relevant costs
Inventory-reporting boundary
Australian AASB 102 paragraph 13 bases fixed production overhead allocation on normal capacity and prevents increasing unit allocation simply because of low production or idle plant. Paragraph 16 excludes abnormal wasted production costs from inventory; paragraph 21 requires standard-cost techniques to approximate cost and be reviewed. The cited compilation was issued December 20, 2021, for periods beginning January 1, 2022 through before January 1, 2027. A setup-per-good-unit sensitivity is therefore not a complete inventory-valuation policy. AASB 102, paragraphs 13, 16, and 21
Related: Cost structure and cost bases · Activity-based costing · Non-recurring engineering charges.