Downtime is any period when an asset, production line or facility is unavailable to do its job. Equipment downtime refers to a single machine or device. Facility downtime or operational downtime refers to a whole site, building or process being stopped, for example a plant shutdown or a data centre outage. How much downtime you have, and why, is one of the clearest measures of maintenance performance.
Planned vs unplanned downtime
| Item | Planned downtime | Unplanned downtime |
|---|---|---|
| Cause | Scheduled work: servicing, calibration, upgrades, changeovers | Breakdowns, faults, accidents, power or supply failures |
| Notice | Days or weeks | None, or minutes |
| Cost | Mostly labour and parts, at a time you choose | Lost output, idle staff, rush parts, overtime, missed deadlines, sometimes safety risk |
| Control | High: you decide when | Low: you react |
| Goal | Keep it short and well timed | Reduce it, mainly by turning it into planned work |
Planned downtime examples
- A quarterly preventive maintenance service on a compressor over a weekend.
- An annual shutdown to inspect a boiler or reline a kiln.
- Taking a scale or gauge out of use for calibration.
- A changeover between product runs on a packaging line.
- A scheduled IT maintenance window for a server or network upgrade.
Common causes of unplanned downtime
- Equipment failure from wear, poor lubrication or missed servicing.
- Waiting: for a technician, for spare parts, for an outside vendor or for a permit.
- Utility failures: power, water, compressed air, network.
- "Can't find it" time. A shared device that exists but cannot be located is, in practice, unavailable.
How to measure downtime and availability
Availability is the share of planned operating time an asset was actually available to run:
From repair history you can also estimate inherent availability as MTBF ÷ (MTBF + MTTR). Decide whether planned downtime counts against availability in your reports. Many teams leave it out of planned operating time, so the figure reflects breakdowns only. Whichever you choose, apply it consistently.
Cost of downtime: a worked example
The true cost of an hour of downtime is usually far more than the repair bill. A simple model adds lost margin and idle labour per hour, then the repair cost:
If lost output can be made up later, use the cost of the overtime needed instead of lost margin. Try your own figures in the free downtime cost calculator.
How to reduce downtime
- Record every downtime event with a cause: breakdown, waiting for parts, waiting for a technician, planned service.
- Move work from unplanned to planned with preventive maintenance on critical assets.
- Cut MTTR: critical spares on hand, clear procedures, and assets that are easy to find and identify.
- Learn from failures to raise MTBF: fix root causes, not only symptoms.
- Time planned downtime well, for example between shifts.
Common mistakes
- Counting only repair time and ignoring waiting time, which is often the larger part.
- Keeping a downtime log that never links to the asset or the work order.
- Mixing calendar and operating time in availability.
- Treating all assets equally. An hour lost on a bottleneck costs far more than an hour on a machine with a standby.
Spreadsheet vs software
A downtime log in Excel or Google Sheets (asset, start, end, duration, cause) is a sensible start and makes the availability formula easy. It breaks down when the log is filled in from memory and durations are not tied to the repair job. Recording downtime minutes on each work order keeps the number with the job and the asset it belongs to.
Downtime in Asetavo
In Asetavo maintenance (Business plan), every work order records downtime minutes alongside parts and labour cost, and each asset's Maintenance tab shows downtime per job and in total. You can export the work-order history to Excel or CSV to calculate availability. Tags and location records cut the time spent looking for equipment. Built-in maintenance KPI reports are on the roadmap.
