How to Audit and Dispute Detention and Demurrage Charges
To audit a detention or demurrage invoice, rebuild the charge yourself: take the free time and rates from the tariff rule or contract that actually applies, take the event dates from terminal and gate records, recompute day by day, then dispute each difference in writing with its evidence. On US trades, the Federal Maritime Commission's billing rule adds two checks before any arithmetic: an invoice missing required information, or issued more than 30 days after the charge was last incurred, does not have to be paid.
- Published
- Sources checked
- Reading time
- 12 min
- Written by
- Mirage Metrics team
Scope: ocean container detention and demurrage billed by carriers, terminals, NVOCCs or forwarders. The regulatory parts apply to US trades only and were checked on September 24, 2026. Elsewhere, the bill of lading, the tariff, the contract and local law govern. Trucking detention (a driver's waiting time) is a different charge and is not covered.
Decision snapshot
- Best suited to
- Freight managers, accounts payable teams, forwarders and shippers who receive detention and demurrage invoices and want to pay only what the terms support.
- Inputs needed
- The invoice, the bill of lading, the applicable tariff rule or contract section, availability notices, terminal and gate event records, appointment and depot records, holds, and any free time extension.
- What can be automated
- Reading invoices and terms, extracting dates, rates and container numbers, pulling event dates from records, recomputing the charge, checking US invoice contents and dates, preparing the reconciliation and the dispute pack.
- What requires human approval
- Deciding which terms apply when documents conflict, arguing closures and refusals, choosing what to dispute and what to pay, sending the dispute, and any escalation.
- When this approach is insufficient
- When event records are missing or contradictory, when the amounts justify legal advice, when the dispute turns on contract interpretation, or outside US trades where no billing rule sets invoice contents or deadlines.
Detention and demurrage, defined
The words are used differently across carriers and regions, so start from the definition in the terms that bind you. Common usage is below. For US trades, the FMC's billing rule defines demurrage and detention together as charges, including per diem, related to the use of marine terminal space or shipping containers, excluding freight charges (46 CFR 541.3).
| Term | What it charges for | Dates it depends on |
|---|---|---|
| Demurrage | The container, usually full, stays in the marine terminal after its free time. On imports: between availability and gate-out. On exports: a full container delivered before the terminal's receiving window, where the terms charge it | Discharge or availability date, last free day, gate-out date |
| Detention | The container stays outside the terminal, in the merchant's hands, after its free time. On imports: from gate-out full to empty return. On exports: from empty pickup to full gate-in | Gate-out date, last free day, empty return (import) or full gate-in (export) |
| Per diem | A name used mainly in the United States for charges on the use of equipment, often what others call detention | Same as detention; check the definition in the terms |
| Combined free time | Some tariffs give one free period covering both, instead of two | Which events start and end the combined period |
Who bills whom, on which terms
The first audit question is whether the right terms are being applied by the right party. A charge billed under a carrier's public tariff when your service contract gives more free time is a wrong-terms error, and no day count will reveal it.
| Billing party | Usually bills | Terms that govern the charge |
|---|---|---|
| Ocean carrier | Merchant named on the bill of lading, or its agent | Bill of lading terms, the carrier's tariff rule, or the service contract section that applies |
| Marine terminal operator | The party the terminal's schedule names, often the consignee or its trucker | The terminal's published schedule |
| NVOCC | Its own customer, often passing on a carrier or terminal charge | The NVOCC's own tariff or arrangement with you, plus the underlying charge |
| Forwarder or customs broker | Its client, passing on a charge it paid or was invoiced | Your agreement with the forwarder; ask for the underlying invoice |
US trades: who may be billed
The FMC rule originally included a section setting who may receive a detention or demurrage invoice. The D.C. Circuit set that section, 46 CFR 541.4, aside on September 23, 2025; the FMC states that the rest of the rule remains in effect (FMC). The invoice must still state the basis for why you are the proper party (541.6(a)(4)).
Documents to gather
| Document | What you take from it | Where it comes from |
|---|---|---|
| The invoice | Every line, the container numbers, dates billed, rates, tariff or contract reference | Billing party |
| Bill of lading | Parties, carrier or merchant haulage, port of discharge | Your file or the carrier portal |
| Tariff rule, service contract section or negotiated arrangement | Free days, calendar or working days, holidays, tiers, start and end events | Carrier or NVOCC; your contract file |
| Free time extensions | Any extra days you negotiated, in writing | Email or contract amendment |
| Arrival notice and availability notice | When the container was declared available, and to whom | Carrier, terminal, forwarder |
| Terminal event records | Discharge, availability, holds, gate-out, gate-in, with timestamps | Terminal portal, equipment interchange receipts |
| Appointment records | Appointments requested, offered, refused; terminal closures | Terminal appointment system, trucker records |
| Empty return instructions | Designated depot, refusals, depot closures | Carrier notices, trucker records |
| Holds and inspections | Customs or other government holds, with dates | Customs broker |
Dates and timestamps to verify
Nearly every dispute comes down to dates. Take each one from a record the billing party did not produce when you can, and note the time zone of every timestamp.
| Date | Meaning | What to watch |
|---|---|---|
| Discharge | When the container left the vessel | Usually not the start of free time on its own; check the terms |
| Availability (imports) | When the container could actually be collected: discharged, released, no holds | The date most often argued; for US imports it must appear on the invoice |
| Last free day | The end of free time as computed from the terms | Recompute it; do not copy it from the invoice |
| Gate-out full (imports) | Container leaves the terminal | Ends demurrage, starts detention in many terms |
| Empty return (imports) | Container returned to the designated depot | Ends detention; check refusals before this date |
| Earliest return date (exports) | First day the terminal accepts the full container for that vessel | For US exports it must appear on the invoice |
| Time zone of each timestamp | Terminal local time, carrier system time, UTC | A late-evening event can move a whole day |
Free time, calendars and time zones
Extract the rule into a small table before recomputing anything. If a field is not stated in the terms, write "not stated" rather than assuming the usual practice, and raise it in the dispute if it changes the result.
| Field | What to look for | Example value (invented) |
|---|---|---|
| Number of free days | Separate for demurrage and detention, or combined | 4 demurrage, 4 detention |
| Day type | Calendar days, or working days excluding weekends and listed holidays | Calendar days |
| Start event | Discharge, availability, the day after, or gate-out | Day after availability; day after gate-out |
| End event | Gate-out, empty return, full gate-in, and whether that day is charged | Day of gate-out and day of return are charged |
| Rates and tiers | Daily rate by container type and size, tier boundaries | Days 1 to 3 at one rate, day 4 onward at a higher one |
| Exclusions | Terminal closures, government holds, strikes, as the terms define them | Not stated: read the rule and the FMC interpretive rule for US trades |
US trades: what the invoice must show
For invoices from ocean common carriers, marine terminal operators and NVOCCs, the FMC's rule sets minimum contents (46 CFR 541.6) and states that an invoice missing any required item eliminates the obligation to pay that charge (541.5). Check these before recomputing:
- Identification: bill of lading number, container numbers, port of discharge for imports, and the basis for billing you
- Timing: invoice date, due date, free time in days, start and end dates of free time, the availability date for imports or the earliest return date for exports, and the specific dates charged
- Rates: total due, the tariff rule, terminal schedule or contract section applied, and the specific rates
- Disputes: a contact for questions and mitigation requests, a link or code to a public page describing what to provide, and the dispute timeframes
- Certifications: that the charges comply with the FMC's rules, and that the billing party's own performance did not cause or contribute to them
- Issued within 30 calendar days of the date the charge was last incurred (30 days from the invoice received, for an NVOCC passing a charge on)
Two further rules frame the dispute: you must have at least 30 calendar days from the invoice date to request mitigation, refund or waiver, and the billing party must try to resolve a request within 30 days of receiving it, unless you both agree otherwise (541.8). The FMC's interpretive rule (46 CFR 545.5) adds the grounds it considers when judging reasonableness: whether the charge still works as an incentive to move cargo, cargo availability, empty return, notice of availability, government inspections, and clear terminology.
The reconciliation table
Put the invoice, the terms, the events and the evidence side by side, one row per element. Each difference gets a status and, if disputed, a reference to its evidence.
| Element | Invoice says | Contract and records say | Difference | Status |
|---|---|---|---|---|
| Container number | MSKU1234565 | B/L and gate records | Same | Match |
| Rule applied | Tariff rule 12 | Service contract section 7 applies to this B/L | Different terms | Wrong terms |
| Free time start | Discharge date | Contract: day after availability | Two days later | Dispute |
| Days billed | 6 | 4 after recomputation | 2 days | Dispute |
| Terminal closure | Charged | Terminal notice: closed that day | 1 day | Argue |
| Invoice issued | 21 days after last charge | 30-day limit, US trade | Within limit | OK |
Worked example: one import container
Illustrative example, invented figures: a 40-foot import container, US trade
Assumptions, all invented. The terms below come from a fictional service contract. The carrier's invoice counts demurrage free time from the discharge date and detention free time from the gate-out day itself, instead of the day after availability and the day after gate-out.
| Term | Value |
|---|---|
| Demurrage free time | 4 calendar days, starting the day after availability; the gate-out day is charged |
| Demurrage rate | $150 a day for charged days 1 to 3, $250 from day 4 |
| Detention free time | 4 calendar days, starting the day after gate-out; the return day is charged |
| Detention rate | $100 a day for charged days 1 to 3, $180 from day 4 |
| Date | Event | Evidence |
|---|---|---|
| Mon Mar 2 | Discharged from the vessel | Terminal record |
| Tue Mar 3 | Available: released, no holds | Terminal record, availability notice |
| Mon Mar 9 | Terminal closed all day | Terminal closure notice |
| Tue Mar 10 | Gate-out full | Equipment interchange receipt |
| Mon Mar 16 | Empty return refused: depot full | Appointment refusal, trucker's record |
| Wed Mar 18 | Empty returned | Equipment interchange receipt |
| Charge | Invoice: days | Invoice | On the terms: days | On the terms | Position after disputes | Position |
|---|---|---|---|---|---|---|
| Demurrage | Mar 7 to 10, 4 days | $700 | Mar 8 to 10, 3 days | $450 | Mar 8 and 10 (Mar 9 closure disputed) | $300 |
| Detention | Mar 14 to 18, 5 days | $660 | Mar 15 to 18, 4 days | $480 | Mar 15 only (Mar 16 to 18 return refused) | $100 |
| Total | $1,360 | $930 | $400 |
How the figures are reached
- Demurrage on the terms: free days Mar 4 to 7, charged Mar 8, 9 and 10, three days at $150, so $450. The invoice started free time at discharge, charged Mar 7 to 10, four days, 3 × $150 + 1 × $250, so $700.
- The terminal was closed on Mar 9, so the container could not be collected that day. Disputing that day on the availability ground leaves two days, $300.
- Detention on the terms: free days Mar 11 to 14, charged Mar 15 to 18, four days, 3 × $100 + 1 × $180, so $480. The invoice started free time on the gate-out day, charged Mar 14 to 18, five days, 3 × $100 + 2 × $180, so $660.
- The depot refused the empty on Mar 16, with a record. Disputing Mar 16 to 18 on the empty return ground leaves one day, $100.
The dispute therefore has two layers: $430 of calculation error ($1,360 invoiced against $930 on the terms), which the terms alone settle, and $530 of argued days ($930 against $400), which depends on the closure notice, the refusal record and, on a US trade, the grounds in 46 CFR 545.5. Also check the invoice itself: had it omitted the availability date, 541.5 would apply to the demurrage line before any of this.
Dispute steps and the tracking register
- Check the invoice before the arithmetic. On US trades: required contents and the 30-day issuance limit. Anywhere: the right party, the right container, the right terms.
- Rebuild the charge from the terms and the records, day by day, in a table you can send.
- Classify each difference: calculation error, wrong terms, events outside your control (closures, refused returns, holds), or missing data on either side.
- Send one dispute per invoice to the contact and through the channel the invoice names, inside its window, with the recomputation and each piece of evidence attached and referenced.
- Pay the undisputed part if your contract or policy requires it, and say so in the dispute.
- Track the response window. On US trades the billing party must attempt resolution within 30 days of your request unless you agree otherwise.
- Escalate when the answer does not address the evidence (see below).
| Field | Example |
|---|---|
| Dispute ID and invoice | D-2026-031, invoice 44810 |
| Billing party and contact | The address or portal the invoice names for disputes |
| Containers | One line per container |
| Amount invoiced, recomputed, disputed | $1,360, $930, $960 |
| Grounds | Wrong start of free time; closure day; empty return refused |
| Evidence attached | Terminal records, closure notice, refusal record, contract section |
| Sent on, deadline to respond | Date sent; the billing party's response window |
| Undisputed amount paid | Per your contract and policy |
| Status and next step | Open, answered, credited, refused, escalated |
When data is missing
A recomputation is only as good as the dates it uses. Be explicit about what you do not have:
- No gate records: you cannot recompute detention. Ask the trucker and the terminal before disputing.
- Terminal and carrier dates disagree: record both, cite the terminal record as the physical event, and ask the billing party which one it used.
- Timestamps without a time zone: do not guess. A late-evening event in local time can be the next day in UTC.
- Terms not found: a dispute that cannot cite the rule applied is weak. Ask for the tariff rule or contract section first.
- Evidence held by your forwarder: request it in writing early, since dispute windows keep running.
When to escalate to a specialist
- The amount, or the pattern across many containers, justifies legal cost.
- The dispute turns on interpreting the contract or the bill of lading, not on dates.
- The billing party ignores the evidence or the response window.
- On a US trade, you are considering a charge complaint to the FMC under 46 U.S.C. 41310 (FMC guidance), or a formal complaint, where under the rule effective September 1, 2026 the carrier bears the burden of showing the charges are reasonable.
- Outside US trades, where local law and the forum clause decide what is possible.
Where Mirage fits
The detention and demurrage calculator does the day-count arithmetic once you have the terms and dates. Mirage's freight invoice audit workflow goes further: it reads carrier invoices, rate tables and contracts, recomputes detention and demurrage against free time terms and gate records when they are available, and shows each discrepancy with its source for your team to approve or dispute. It is built on the document pipeline running at Transwin. Mirage has not published a dispute outcome from this workflow, and it does not send disputes or file complaints on your behalf.
Questions readers ask
What is the difference between detention and demurrage?
In common usage, demurrage is charged while a container stays in the terminal beyond its free time, and detention while it stays outside the terminal, in the merchant's hands, beyond its free time. Carriers define the terms, and sometimes combine them, in their tariffs and contracts, so read the definition that applies to your bill of lading. The US Federal Maritime Commission's rules treat both, including per diem, as charges for the use of terminal space or containers.
Do I have to pay a demurrage invoice that arrives late?
For charges covered by the FMC's billing rule (46 CFR Part 541), which applies to invoices issued by ocean common carriers, marine terminal operators and NVOCCs, an invoice issued more than 30 calendar days after the charge was last incurred does not have to be paid. An NVOCC passing on a charge has 30 days from the invoice it received. Outside US trades, the tariff, the contract and local law decide.
How long do I have to dispute a detention or demurrage charge?
Under 46 CFR 541.8, the billing party must give you at least 30 calendar days from the invoice date to request mitigation, refund or waiver, and must try to resolve a request within 30 days of receiving it, unless both sides agree otherwise. The invoice itself must state the dispute timeframes and where to send a request. Outside US trades, check the carrier's terms.
Can I be charged detention when the depot refuses the empty container?
For US trades, the FMC's interpretive rule (46 CFR 545.5) says that, absent extenuating circumstances, practices that impose detention when empty containers cannot be returned are likely to be found unreasonable. Keep the evidence of the refusal: the appointment system record, the depot's notice, the trucker's log.
Where do I complain if the carrier will not resolve a US dispute?
The FMC accepts charge complaints under 46 U.S.C. 41310 from shippers, consignees, truckers or others who paid or were invoiced, by email to chargecomplaints@fmc.gov, with the invoices, bills of lading and proof of payment. A final rule effective September 1, 2026 confirms that a charge complaint can also follow the traditional complaint routes, where the carrier bears the burden of showing its demurrage and detention charges are reasonable. For large or repeated amounts, involve a maritime lawyer.
Sources and scope
Checked on . Scope: US federal rules for ocean detention and demurrage billing and disputes. The eCFR text used is the version in force on September 1, 2026. Non-US trades are governed by the terms and local law and are not covered here.
- 46 CFR Part 541, Demurrage and Detention (eCFR): definitions, required invoice contents, 30-day issuance, 30-day mitigation window, consequence of missing information
- FMC, U.S. Court of Appeals issues decision on demurrage and detention billing practices: 46 CFR 541.4 (who may be billed) set aside on September 23, 2025; the rest of the rule in effect
- 46 CFR 545.5, Unjust and unreasonable practices with respect to demurrage and detention (eCFR): incentive principle, empty container return, notice of availability, government inspections, clear terminology
- FMC, Guidance on Charge Complaint Interim Procedure: who may file, how, supporting documents, remedies
- Federal Register, Charge Complaint Procedures, final rule effective September 1, 2026: traditional complaint route and the carrier's burden on reasonableness
This guide describes an audit and dispute procedure. It is not legal advice, and for significant amounts a maritime lawyer should review the terms and the dispute.
Related on this site
- Detention and demurrage calculator: compute a charge from free time and tiers
- Freight invoice audit: every carrier invoice checked before payment
- Logistics: all freight document workflows
- Carrier onboarding document verification: the other logistics guide
Send us a batch of detention and demurrage invoices
With the contract terms and the gate records for the same containers, we will return the recomputed charge for each line and the differences with their evidence, so you can decide what to dispute.
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