To calculate downtime in production, divide total downtime minutes by total planned production time, then multiply by 100 to get a downtime percentage: Downtime % = (Total Downtime ÷ Planned Production Time) x 100.

For example, a machine scheduled to run 480 minutes in a shift that loses 60 minutes to stoppages has a downtime rate of 12.5%. Most manufacturers track this by machine, shift, and reason code rather than as a single plant-wide number, since that's what actually points to where the time is being lost.

The Production Downtime Formula

The basic formula is straightforward:

• Downtime Percentage = (Total Downtime Minutes ÷ Planned Production Time in Minutes) x 100

To use it, two numbers need to be accurate:

• Planned production time: the total time a machine is scheduled to run, excluding scheduled breaks, shift changes, and planned maintenance
• Total downtime: every minute the machine was scheduled to run but wasn't, for any reason, whether that's a jam, a changeover that ran long, a material shortage, or an unplanned repair

Example: A machine is scheduled for an 8-hour shift (480 minutes). It experiences a 25-minute jam, a 20-minute changeover overrun, and a 15-minute unplanned repair, totaling 60 minutes of downtime.

Downtime % = (60 ÷ 480) x 100 = 12.5%

Planned vs. Unplanned Downtime

Not all downtime should be counted the same way, since planned and unplanned downtime point to different problems.

• Planned downtime includes scheduled maintenance, tooling changes, shift breaks, and planned changeovers. This time is usually excluded from the "planned production time" used in OEE and downtime calculations, since it was never expected to be productive.
• Unplanned downtime includes breakdowns, jams, material shortages, quality holds, and any stoppage that wasn't scheduled. This is the number that matters most for improvement work, since it represents time the plant expected to have and lost.

Mixing the two into a single downtime figure hides the real problem. A plant with a lot of planned maintenance but very little unplanned downtime is in a fundamentally different position than one with the opposite mix, even if the total downtime hours look similar.

How Downtime Fits into OEE

Downtime feeds directly into the availability component of OEE (Overall Equipment Effectiveness), one of the three factors, along with performance and quality, used to calculate the metric.

• Availability = (Planned Production Time − Downtime) ÷ Planned Production Time

Using the earlier example: Availability = (480 − 60) ÷ 480 = 87.5%.

That availability score then multiplies with performance and quality to produce overall OEE. This is why downtime tracking and OEE tracking are usually built into the same system rather than calculated separately, since they rely on the same underlying data.

Tracking Downtime Manually vs. Automatically

Manual downtime tracking uses paper logs or spreadsheets, with an operator noting start and stop times along with a reason. It's workable at small scale but tends to break down for a few reasons:

• Short stops get missed or rounded. A two-minute jam that happens ten times a shift often doesn't get logged at all, but it can add up to more lost time than a single 20-minute breakdown.
• Timestamps aren't precise. An operator writing down "around 2:15" introduces error into every downtime calculation that follows.
• Reason codes get generalized. "Machine issue" doesn't provide enough detail for root cause analysis, even if the total downtime minutes are accurate.

Automated downtime tracking solves this by detecting machine state changes directly from the equipment, timestamping each event to the second, and prompting for (or automatically assigning) a reason code. Platforms like Caddis's downtime tracking report stoppages within five seconds of occurrence, which is precise enough to catch short stops that manual logs consistently miss.

What to Do with Downtime Data Once You Have It

Calculating a downtime percentage is only useful if it leads to action. A few ways plants use the number:

• Rank downtime by reason code to find the single biggest contributor to lost time, rather than treating all downtime as one undifferentiated problem
• Compare downtime across shifts to spot whether a specific shift, crew, or handoff period consistently loses more time than others
• Track downtime trends over weeks or months to confirm whether an improvement initiative, like a new changeover procedure, is actually working
• Set downtime alerts so a supervisor or maintenance technician is notified the moment a machine goes down, rather than finding out at the end of the shift

Frequently Asked Questions

How do you calculate downtime in production?

Divide total downtime minutes by planned production time in minutes, then multiply by 100. A machine scheduled for 480 minutes that loses 60 minutes to stoppages has a downtime rate of 12.5%.

What is a good downtime percentage in manufacturing?

There's no universal benchmark, since it depends heavily on the industry and equipment type, but many discrete manufacturers target unplanned downtime under 10%. What matters most is tracking the trend over time and identifying the specific causes driving it.

Does planned maintenance count as downtime?

Planned maintenance is typically excluded from the planned production time used in downtime and OEE calculations, since that time was never expected to be productive. It should still be tracked separately for maintenance planning purposes.

What's the difference between downtime and availability?

Downtime is the raw time lost to stoppages. Availability is the percentage of planned production time that remained after subtracting downtime, and it's one of the three components used to calculate OEE.

How can manufacturers reduce unplanned downtime?

Reducing unplanned downtime starts with accurate reason code data to identify the biggest contributors, followed by targeted fixes, whether that's a maintenance schedule change, a changeover process improvement, or predictive maintenance based on machine condition data.

Get Started

Calculating downtime by hand works for a single machine on a single shift. It stops working the moment a plant runs multiple machines, multiple shifts, or wants to catch the short stops that manual logs miss. Automated downtime tracking handles the calculation in real time and shows exactly where the time is going.

To see automated downtime tracking on your own machines, book a free demo with Caddis Systems.