Why do overtime hours exceed shortfall divided by rate?

Output per overtime hour runs below the regular shift: fatigue, fewer support staff and more handovers. An 85% allowance turns 40 units at 20 an hour into 2.35 hours instead of 2. Update the allowance from your own overtime runs.

What is a realistic overtime efficiency?

Measure good units made on overtime divided by overtime hours over several weeks. First overtime hours often hold near 90%, and long weeks slide toward 80%. Enter the rate you actually see, not the one you hope for.

Should the shortfall include rework and scrap?

Yes if they are units you owe and cannot ship. Rework units often pass twice, so they may need time on top of the shortfall. Convert every extra pass into the units the line must produce.

When is a second shift better than overtime?

When required hours sit above your limit week after week, or when overtime output per hour keeps falling. A second shift adds capacity without fatigue compounding, though it brings hiring, handover and supervision costs.

Lean Manufacturing & Operations calculator

Overtime Hours Requirement Calculator

Work out the overtime hours a production shortfall needs, allowing for the lower output an extra shift actually delivers. Enter the shortfall, the regular-shift rate, overtime efficiency and the limit you will authorize.

What this calculator does

Overtime hours to recover a shortfall, with the fatigue loss and the hours past your limit.

Formula used

Hours at regular rate = production shortfall ÷ regular-shift rate
Required overtime hours = hours at regular rate × 100 ÷ overtime efficiency
Hours lost to overtime fatigue = required overtime hours − hours at regular rate
Hours above your limit = MAX(0, required overtime hours − overtime limit)

Inputs explained

Production Shortfall: Good units the shift still owes against its plan or order.
Regular-Shift Rate: Good units the regular shift makes per run hour.
Overtime Efficiency: Expected overtime output as a percent of the regular rate.
Overtime Limit per Shift: The most overtime you will authorize in one shift.

How to use the result

Best suited to planning weekend catch-up, checking a shortfall against policy, comparing overtime with a second shift.
Repeated or long overtime drops efficiency further, so rerun the numbers after two weeks. The limit recovers units at the overtime rate; schedule support and material before you rely on it.

Current U.S. benchmarks

U.S. manufacturing runs at 75.7% of capacity (Federal Reserve, Aug 2026). New factory orders are up 8.5% year over year (Census).

Common questions

Why do overtime hours exceed shortfall divided by rate? Output per overtime hour runs below the regular shift: fatigue, fewer support staff and more handovers. An 85% allowance turns 40 units at 20 an hour into 2.35 hours instead of 2. Update the allowance from your own overtime runs.
What is a realistic overtime efficiency? Measure good units made on overtime divided by overtime hours over several weeks. First overtime hours often hold near 90%, and long weeks slide toward 80%. Enter the rate you actually see, not the one you hope for.
Should the shortfall include rework and scrap? Yes if they are units you owe and cannot ship. Rework units often pass twice, so they may need time on top of the shortfall. Convert every extra pass into the units the line must produce.
When is a second shift better than overtime? When required hours sit above your limit week after week, or when overtime output per hour keeps falling. A second shift adds capacity without fatigue compounding, though it brings hiring, handover and supervision costs.

Related guides

Last reviewed 2026-10-01.