Downtime Percentage

Excel Formulas › Manufacturing & Operations

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Downtime percentage is unplanned stop time over planned production time — the lost-availability metric behind OEE. It quantifies how much potential run time disappears to breakdowns and changeovers.

Quick formula: downtime from stop time and planned time:
=downtime_minutes / planned_minutes
Unplanned stop minutes over planned minutes, as a percentage. Availability is its complement.

The example

48 min down of 480 planned.

AB
1ItemValue
2Downtime48
3Planned480 → 10%

The formula

The formula:

=B2 / B3 // downtime ÷ planned time

How it works

How it works:

  1. Sum unplanned stop time (breakdowns, jams, waiting) over the period.
  2. Divide by planned production time for the downtime percentage.
  3. Availability — the OEE factor — is 1 - downtime%.
  4. Pareto downtime by reason code with SUMIF to target the biggest losses.

Reason codes turn downtime into an action list. Logging each stop with a reason (changeover, jam, material-out, breakdown) and totalling minutes per reason with SUMIF reveals where availability really leaks. Usually a couple of reasons dominate — quick changeover (SMED) or a recurring jam fix recovers most of the lost time.

Try it: interactive demo

Live demo

Downtime and planned minutes.

Downtime · Availability

Variations

Availability

OEE factor:

=1 - downtime_minutes / planned_minutes

MTBF

Mean time between failures:

=run_time / number_of_failures

Downtime by reason

Pareto:

=SUMIF(reason, "Changeover", minutes)

Pitfalls & errors

Unplanned only. Exclude planned maintenance and no-demand from downtime if measuring availability.

Same period. Downtime and planned time over the same window.

Log reasons. Without reason codes you can’t act on the number.

Practice workbook

📊
Download the free Downtime Percentage practice workbook
A downtime sheet with the availability, MTBF, and by-reason variants, plus 4 challenges with answers. No sign-up required.

Frequently asked questions

How do I calculate downtime percentage in Excel?
Divide unplanned stop minutes by planned minutes: =downtime_minutes / planned_minutes. 48 of 480 is 10%.
How does downtime relate to availability?
Availability (the OEE factor) is its complement: =1 - downtime% .
How do I find the biggest downtime cause?
Total minutes per reason code with SUMIF and sort — a few reasons usually dominate.

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