How to calculate production shortfall during a shift

Separate the current gap from the projected shortfall

A target-versus-actual board can compare accumulated planned good output with completed good output at the same time. Vorne’s production-target guide describes that comparison. For example, 700 good units planned by 2 pm and 640 completed gives a current gap of 60 units.

That does not tell you the final shift shortfall. There may still be enough time to catch up, or a planned changeover may make the eventual gap larger. Use the remaining time and rate to estimate the shift-end position separately.

Collect six inputs with the same production scope

• Shift target: the whole good-unit count required from this line or process.
• Good units completed: accepted output already made against that target.
• Gross running rate: units per hour while running, before future scrap.
• Hours remaining: clock time until shift end, including remaining stops.
• Remaining planned stops: minutes with zero production still ahead.
• Expected future scrap: the proportion of upcoming gross output you expect will not become good units.

Keep the unit and product scope consistent. Do not combine counts of unlike products as if their production rates were interchangeable.

Use the production shortfall formula

Keep intermediate values at full precision. If you are counting complete units, round the final projected output down before subtracting it from the whole-unit target. The MagicWand shift-shortfall calculator uses that convention.

Worked example: 115 good units short

This is an illustrative single-line scenario, not a customer result.

Productive time is 3 − 30 ÷ 60 = 2.5 hours. Additional gross output is 100 × 2.5 = 250 units. At 98% expected yield, additional good output is 250 × 0.98 = 245 units.

Projected shift-end output is 640 + 245 = 885 good units. The projected shortfall is 1,000 − 885 = 115 good units.

Calculate the running rate required to close the gap

First find the remaining good units needed: maximum of zero and (target − completed good units). Divide this by productive hours and expected yield:

Required gross running rate = remaining good units needed ÷ [productive hours × (1 − future scrap percentage ÷ 100)].

In the example, 360 ÷ (2.5 × 0.98) = about 146.94 gross units/hour. Rounded up to the next 0.1 unit/hour, that is 147.0 units/hour. It is a mathematical requirement. Check it against the line’s demonstrated capacity, quality requirements and approved operating limits before treating it as an achievable plan.

If no productive time remains, or expected yield is zero, there is no finite running rate that can make the remaining good units. If the target is already achieved, the required additional rate is zero.

Compare pace and stop-time scenarios separately

Keeping the 2% future scrap assumption, these hypothetical changes produce different outcomes:

The combined scenario still misses the target. The arithmetic helps make that visible before an operating decision. It does not establish that a faster pace or shorter stop is feasible.

Avoid double-counting losses

• Do not apply scrap twice. If the rate already measures good output after scrap, deducting scrap again understates the projection.
• Do not subtract stops twice. A shift-average rate that includes downtime is different from a rate measured only while running.
• Do not deduct past stops from future time. Enter only stops still ahead.
• Do not re-estimate completed units. Keep accepted output as recorded; future scrap applies to future production.
• Do not keep one rate through a known product change without checking it. Calculate separate segments when future products have different rates.

Use the result to frame the next shift conversation

Share the target, completed good count, remaining productive time, running rate and scrap assumption with the gap. Add the time at which those assumptions were recorded. Ask which assumption could change and who can confirm it.

Calculate and share your own shift scenario. The tool uses constant-rate arithmetic rather than live factory data. For the product workflow, explore MagicWand shift forecasting and recovery. To understand the causes behind lost output, read production downtime versus speed loss.

Keep a consistent shift review record

Use the same fields each time you revise a scenario. This blank worksheet records a timestamp, target, completed good units, gross running rate, remaining stops, scrap assumption, evidence and an owner.