Freight

Detention Cost Exposure

Calculate real monthly detention cost exposure using free-time-netted billable hours, not the full dwell time a naive estimate would charge.

Average dwell timehours a trailer sits at the dockFree time allowancehours before detention startsDetention rate$/hour once billableShipments per monthshipments/month at this dwell pattern

Moderate exposure$6,000/mo

Billable hours2 hr

Cost per shipment$150

Resources

Reference Landed Cost: The Duty Line Everyone Underestimates A $10 unit cost, $8 freight, 25% duty rate. Duty on cost alone: $2.50. Duty on the real dutiable base, cost plus freight: $4.50. The $2 gap is not a rounding error, it is a fixed mistake in what the duty rate applies to.

How this works

Detention charges apply only to dwell time beyond the carrier's free time allowance, not to the full dwell time. Billable hours times the detention rate gives cost per shipment, multiplied by monthly shipment volume gives total monthly exposure.

Key terms

Free time: the grace window before detention charges start accruing.
Billable detention hours: dwell time beyond the free time allowance, the only hours actually charged.

Assumptions

Free time and rate are uniform across all shipments on the lane

Limitations

One lane, one carrier's terms, not a multi-carrier accessorial audit

Sources

Standard carrier detention/demurrage billing practice.

Worked example

A naive estimate that charges the full 10-hour dwell time against a $75/hour rate reports $750/shipment, $30,000/month, a 5x overstatement. The free-time-netted calculation correctly bills only the 2 billable hours past the 8-hour free time allowance, $150/shipment, $6,000/month.

Common use cases

Estimating real detention cost exposure before negotiating carrier terms
Deciding whether dock-scheduling changes are worth the investment
Comparing detention risk across freight mode or carrier options