Planned versus unplanned split—who codes stops?
Operators code at machine; planner validates weekly. Miscoded PM as breakdown distorts capital and staffing decisions.
ZBI Business Control Library
Downtime %
Downtime %: plain-English definition, formula, worked example, how to interpret the result, peer-based benchmark guidance, common mistakes, and management actions in the ZBI Business Control Library.
What is Downtime %?
Downtime percent is lost production hours divided by planned production hours—time the line was scheduled to run but did not. It includes breakdowns, changeovers beyond standard, material waits, and quality holds if they stop the clock. At PakProm d.o.o., 96 downtime hours against 1,600 planned production hours in May is 6% downtime. I split planned maintenance from unplanned stops because cutting PM to hit utilization targets converts 6% downtime into a 14-hour breakdown two months later.
Why Downtime % matters
Downtime is capacity you already paid for—salary, overhead, and customer promise time that produced nothing. At 6% on 1,600 planned hours, PakProm lost 96 hours on the constraint flexo line—roughly 4.8 shifts of output that sales already quoted into June delivery dates. Micro-stoppages under five minutes often never hit the log but sum to more lost time than one major breakdown on the report. Customers see downtime as late shipments and emergency freight. Maintenance sees deferred PM. Finance sees overtime to catch up—6% downtime plus 8% overtime is a margin squeeze ops explains as 'bad luck.'
Formula and variables
Downtime % = Downtime Hours ÷ Planned Production Hours × 100
Downtime hours — hours not producing when production was scheduled (define whether changeover overrun counts).
Planned production hours — scheduled run time on the calendar, excluding holidays not in the plan.
Excel: =IFERROR(B2/B3*100,0)
Real business example
PakProm d.o.o. May summary on flexo Line 2: 96 downtime hours logged (32 unplanned breakdown, 28 material wait, 22 changeover overrun, 14 quality hold); 1,600 planned production hours per the frozen monthly schedule. Downtime percent = 96 ÷ 1,600 × 100 = 6%. April was 4.2%—May's step-up traces to a bearing failure not on the PM list and three days waiting on a die delivery. Plant manager adds the bearing to critical spares and freezes changeover standard work review before approving June overtime.
How to interpret the result
Downtime percent measures schedule loss—focus on the constraint and split planned versus unplanned.
- 6% on the bottleneck caps throughput; plant average downtime can look fine while orders ship late.
- Micro-stoppages over two minutes should count or cumulative loss exceeds major events on the report.
- Material wait downtime feeds back to inventory and supplier OTIF—not only maintenance.
- Cutting planned PM to reduce downtime percent often raises unplanned hours within eight weeks.
Benchmark context
Many discrete packaging lines target 4–8% total downtime including planned changeovers; unplanned above 5% on the constraint for four weeks warrants escalation. Benchmark against your own trailing quarter on the same shift pattern—not world-class OEE posters. Job shops with daily engineering changes accept higher changeover downtime if on-time production still clears 94%.
Red flags
- Unplanned downtime above 8% on the constraint four weeks running—schedule misses and premium freight follow.
- Planned maintenance cut to hit utilization targets—breakdown hours exceed saved PM time within two months.
- Micro-stoppages not logged—five-minute events sum to more lost hours than major breakdowns on the report.
- Downtime low on non-constraints while bottleneck starves—plant average looks fine, orders ship late.
- 96 hours downtime month with no top-three reason code review—repeat failures next month guaranteed.
Common mistakes
- Logging only breakdowns over 30 minutes—micro-stops sum to more than major events.
- Planned maintenance cut to hit utilization—breakdown hours exceed saved PM within two months.
- Downtime measured plant-wide while bottleneck starvation drives late orders.
- Changeover overrun coded as 'planned' without standard time—true loss hidden.
- Material wait excluded from downtime—blame inventory planning never gets schedule recovery time.
What should management do next?
- Split planned and unplanned downtime on constraint; publish both weekly.
- Code micro-stoppages over two minutes; review cumulative weekly.
- Relate top three downtime codes to spare parts and PM schedule review.
- Escalate unplanned constraint downtime above 5% for four weeks to plant manager.
- Do not cut PM to hit utilization—track breakdown hours versus saved PM.
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FAQ
What unplanned downtime level triggers TPM review?
Constraint unplanned above 5% for four weeks or any single event over 8 hours on bottleneck.
Do micro-stoppages belong in downtime?
Yes if over two minutes or if cumulative micro-stops exceed 30 minutes per shift—otherwise you understate 6% toward 10%+ real loss.
Material wait counted as downtime or inventory KPI?
Both. Log as downtime for schedule recovery; root-cause to supplier or internal planning in the same review.
How does downtime link to spare parts stock?
Top three breakdown codes get spare parts review—MTTR reduction often beats adding more PM hours blindly.
Summary
Downtime percent shows how much scheduled production time you lost. Measure on the constraint, split planned and unplanned, and code small stops honestly—before overtime becomes the recovery plan.
Reviewed by ZBI Business Control Library · Last updated 2026-06-15