Detention vs. demurrage: what's the difference — and what you can actually check

The short version

Both are charges for using time you weren't supposed to use — the difference is where the container is when the clock runs past your free time.

• Demurrage is typically charged when a container sits inside the terminal past the allowed free time — for imports, the loaded box waiting to be picked up after it became available; for exports, cargo delivered to the terminal too early.
• Detention is typically charged when a container is outside the terminal past the allowed free time — you took the loaded import container out and kept it too long, or you're holding an empty past the date it was due back.

Carrier tariffs and service contracts define the exact terms, and some carriers bundle both under one label. What matters legally is that the FMC's billing rule (46 CFR Part 541) governs invoices for both — so the same content and timing checks apply whichever one you were billed for.

Why the distinction matters for a dispute

The FMC's separate interpretive rule, 46 CFR § 545.5, looks at whether a charge actually serves its purpose as an incentive to keep cargo and equipment moving. Where it can't serve that purpose, the charge is on weaker ground. In the rule's own words, practices that impose detention “when it does not serve its incentivizing purposes, such as when empty containers cannot be returned, are likely to be found unreasonable” absent extenuating circumstances.

That's a reasonableness standard, not an automatic waiver — it means the Commission weighs the circumstances, so the detention-vs-demurrage label matters: detention billed while an empty genuinely couldn't be returned, or demurrage counted through days the terminal wasn't operating, are exactly the situations the rule flags as questionable.

What to check on either invoice

Whichever charge it is, run the same three checks before paying.

1. Does the invoice contain everything § 541.6 requires?

The rule requires specific minimum information in four buckets — identifying (BOL and container numbers, port of discharge, why you're the liable party), timing (invoice and due dates, allowed free time, free-time start/end, availability or earliest-return date, and the specific dates charged), rate (total due, the tariff or contract rule the rate comes from, and the rate itself), and dispute (contact info, a URL to the dispute process, and defined timeframes). This is where the label matters again: the invoice has to state which charge it is and the rule it's based on. Under 46 CFR § 541.5, “failure to include any of the required minimum information in this part in a demurrage or detention invoice eliminates any obligation of the billed party to pay the applicable charge.”

2. Is the invoice on time?

A billing party must issue the invoice within 30 calendar days of the date the charge was last incurred; if it doesn't, “the billed party is not required to pay the charge” (46 CFR § 541.7(a)). An NVOCC passing a charge through gets 30 days from the invoice it received (§ 541.7(b)).

3. Is the math right — and do you have time to dispute?

Recompute the free time against your contract's terms: does the printed last free day equal the availability (or earliest-return) date plus your contractual free days, and do the billed days include weekends or closures when pickup or return wasn't possible? (Whether those days burn free time depends on your tariff/contract.) You have at least 30 calendar days from invoice issuance to request mitigation, refund, or waiver, and the billing party must attempt to resolve the request within 30 calendar days of receiving it, unless both sides agree to a later date (46 CFR § 541.8).

Bottom line

Demurrage vs. detention changes which argument fits your situation, but not whether you can check the bill: the same FMC content, timing, and reasonableness rules apply to both. The fastest way to see if a specific invoice has recoverable charges is to recompute the dates and check them against the § 541.6 requirements — which is exactly what the free audit below does.