Machine downtime cost calculator: lost contribution, idle labour and restart scrap per hour of downtime, with cost per minute and the annual figure.
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Short answer
Downtime cost per hour is lost units times contribution margin, plus idled operators times their loaded rate, plus restart scrap. With 18.5 hours down across 14 stops on a 240-unit-per-hour line at $4.85 contribution, the period costs $31,793, which is $1,719 per downtime hour, or $28.64 a minute.
Downtime is only expensive if you can name the number. Once you can, a $4,000 sensor and a spare motor on the shelf stop being a capex argument and start being arithmetic.
Enter your downtime hours, the number of stops, the rate the line runs at and what a unit contributes. The calculator returns the cost for the period, the cost per downtime hour and per minute, the annualised figure, and how the total splits between lost output, idle labour and restart scrap.
It values lost output at contribution margin, not at sell price. Fixed cost is incurred whether the line runs or not, so counting it as lost overstates downtime, sometimes by a factor of three.
Your numbers
Used only to annualise the total.
Result
Downtime cost this period
$31,793
$1,718.54 per downtime hour · $28.64 per minute
Lost units4,440
Cost per stop$2,270.93
Average stop length1.32 h
Availability95.6%
Annualised downtime cost$381,516
Cost per minute$28.64
Fixed overhead and depreciation are excluded — they are incurred whether the line runs or not.
Cost component
Amount
Share
Per hour down
Lost contribution
$21,534
67.7%
$1,164.00
Idle labour
$1,887
5.9%
$102.00
Restart scrap
$8,372
26.3%
$452.54
Total
$31,793
100.0%
$1,718.54
lost units = 18.5 h × 240 units/h = 4,440
lost contribution = 4,440 × $4.85 = $21,534
idle labour = 18.5 h × 3 operators × $34.00 = $1,887
total = $31,793 → $1,718.54 per downtime hour → $28.64 per minute
95.6% availability is strong, though the stoppages still cost $381,516 a year at $28.64 a minute. This only holds if the lost units are genuinely lost — if you make them back later in the week without overtime, the real cost is closer to $10,259.
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Unplanned stoppage time inside scheduled production. Planned maintenance and unscheduled shifts do not belong here.
Output rate
Units per hour the line achieves when it is running. Use the demonstrated rate, not the nameplate rate.
Contribution per unit
Sell price minus variable cost. Not gross margin, and never the sell price — fixed cost is incurred whether the line runs or not.
Operators idled
People paid but unable to work. Zero if they are redeployed to productive work during the stop.
Loaded rate
Hourly wage plus payroll tax and benefits.
Restart scrap
Units lost bringing the process back to specification after each stop, valued at their standard cost.
Lost contribution is the honest measure only when the output is genuinely lost. If the machine is not your constraint and you make the units back later in the week, the real cost is the overtime and expediting you spent making them, not the contribution — which is usually much smaller.
Worked example
Downtime in the period
18.5 hours across 14 stops
Output rate when running
240 units/hour
Contribution per unit
$4.85
Operators idled
3 at $34.00/hour
Restart scrap
65 units per stop at $9.20
Result
$31,793 for the month · $1,718.54 per downtime hour · $28.64 per minute
18.5 hours at 240 units/hour is 4,440 lost units, worth $21,534 of contribution. Three operators idle for 18.5 hours at $34.00 adds $1,887. Fourteen restarts scrapping 65 units at $9.20 adds $8,372. Total $31,793, or $1,718.54 per downtime hour. Note that restart scrap is 26.3% of the total — it is driven by the number of stops, not their length.
The three components, and when each is zero
Most downtime cost claims are wrong because one of these three is counted when it should not be. The honest version tests each component separately.
Component
How to value it
When it is genuinely zero
Lost contribution
Lost units × (sell price − variable cost).
The machine is not the constraint and the output is made up later in the week without extra cost.
Always. These are incurred whether the line runs or not, so they are not caused by the stop.
Cost per stop against cost per hour
The two figures point at different fixes. Restart scrap is driven by the number of stops; lost contribution and idle labour are driven by their length. On the seeded numbers restart scrap is 26.3% of the total across 14 stops, which means seven short stops cost more than one long one of the same duration.
Lost contribution dominates — attack stop duration: spares availability, response time, operator authority to call maintenance.
Idle labour dominates — the fix is scheduling, not reliability. Give operators defined work for a stop.
Downtime is the same number as your availability loss
Availability in OEE is scheduled time minus downtime, divided by scheduled time. On the seeded inputs, 18.5 hours lost from 420 scheduled gives 95.6% availability. That ties the money in this calculator to the percentage on the shop-floor board, which is what makes the case land with operations rather than only with finance. Cross-check the full picture in the OEE calculator.
The same hours also surface in your labour efficiency variance, because operators waiting are hours charged with no output allowed against them. If the two numbers are similar in size, you have found the cause of your unfavourable variance without arguing about operator speed.
Turning the number into a decision
Cost per minute is the figure to carry into the maintenance conversation. At $28.64 a minute, a spare drive that saves four hours of waiting once a year pays for itself at $6,874 — and a repeat fault costing 90 minutes a month is a $30,931 annual line item that nobody has ever seen written down.
The hard part is getting reliable downtime data by asset and reason code, then valuing it at the right contribution per unit. With ERPray you ask for it: "unplanned downtime hours and stop count by work centre last quarter, with contribution per unit for the items each one runs" — computed from your own records, with the query shown so you can check which reason codes it counted as unplanned.
Frequently asked questions
How do you calculate the cost of machine downtime?
Add three things: lost units (downtime hours × output rate) valued at contribution margin per unit, idled operators × downtime hours × their loaded hourly rate, and restart scrap per stop valued at standard cost. Divide by downtime hours for cost per hour. At 18.5 hours the seeded example costs $1,718.54 per hour.
Should downtime cost use contribution margin or sell price?
Contribution margin: sell price minus variable cost. Fixed overhead and depreciation are incurred whether the machine runs or not, so including them counts cost the stop did not cause. Using sell price typically overstates downtime by three to four times and produces a business case the P&L will never confirm.
What is a good downtime percentage?
Read it as availability instead: scheduled time minus downtime, over scheduled time. Above 90% is respectable for most discrete manufacturing and 95% is strong. Continuous process plants expect higher. The trend and the stop count matter more than the level, because frequent short stops cost more than the hours suggest.
Does planned maintenance count as downtime?
Not in this calculation. Planned maintenance is removed from scheduled time in the OEE convention, so it is not an availability loss. Count it here only if it overran its window or was scheduled inside production time you had committed to an order. Mixing planned and unplanned makes the trend useless.
How do I include idle labour in downtime cost?
Only for people who are paid and genuinely cannot work: operators × downtime hours × loaded hourly rate. If they are redeployed to cleaning, training or another cell, the cost is zero and counting it double-counts. Loaded rate means wage plus payroll tax and benefits, not the base wage.
Why does restart scrap matter more than downtime hours?
Because it scales with the number of stops, not their length. A process that scraps 65 units on every restart loses the same on a two-minute stop as on a two-hour one. When restart scrap is a large share of the total, reducing minor stops beats reducing repair time, and the two need different fixes.
This calculator needs you to find the inputs first. ERPray pulls them from your own ERP account and computes the answer live — with the exact query shown so you can check it.