One container can become an expensive accounting problem before it becomes a logistics problem. A few days of terminal storage, an equipment-return delay, or a disputed “per diem” charge can turn into thousands of dollars—but the invoice may arrive after the shipment is closed, separated from the bill of lading, and routed to the wrong person.
That is why demurrage and detention invoices deserve their own control process. They are not ordinary freight bills. You need to connect each charge to a container, a free-time calculation, a contract or tariff, and the operational event that supposedly caused the fee.
The Federal Maritime Commission (FMC) has collected quarterly data from nine major ocean carriers for years. Those carriers collected roughly $15.4 billion in detention and demurrage charges between April 2020 and March 2025. The amount has fallen from its pandemic-era peak, but the scale makes one point clear: these charges are large enough to affect margins, inventory cost, and cash flow even for a small importer.
This guide explains what to check before paying, how to dispute a questionable bill, and how to build the evidence trail into your bookkeeping.
Demurrage and detention are different charges
The terms are often bundled together, but they describe different uses of a container.
- Demurrage generally relates to keeping an import container in a marine terminal beyond the allowed free time.
- Detention generally relates to keeping the carrier’s equipment outside the terminal longer than the allowed period, including a delay in returning an empty container.
Your invoice may use “per diem” or another carrier-specific label. Read the underlying tariff, service contract, or negotiated arrangement rather than relying only on the description in an accounts-payable inbox.
The distinction matters because each charge has its own clock. For demurrage, you may need to establish when the cargo was actually available and when free time ended. For detention, you may need the pickup date, the permitted use period, the appointment history, and proof of when the empty equipment was returned or when a return was first made available.
What the current FMC invoice rule gives you
Part 541 of Title 46 of the Code of Federal Regulations establishes minimum information for demurrage and detention invoices issued by an ocean common carrier, marine terminal operator, or non-vessel-operating common carrier (NVOCC).
Three protections are especially useful to an importer:
- The bill must contain enough accurate information for you to understand the container, dates, rates, and dispute process.
- The billing party generally has 30 calendar days to issue the invoice after the date the charge was last incurred. For an NVOCC passing through a carrier invoice, the timing rule uses the date the NVOCC received the underlying invoice.
- You must receive at least 30 calendar days from the invoice date to request mitigation, a refund, or a waiver.
If a bill omits required minimum information, the rule says the billed party is not obligated to pay the applicable charge. Treat that as a reason to open a documented dispute—not as a reason to silently delete the invoice.
Do not rely on outdated “proper party” summaries
Older explanations of the rule often say that an invoice may be sent only to one of two categories of party. The current eCFR marks that specific section as reserved, so an importer should not treat that old summary as a complete statement of the law.
Instead, verify the commercial facts:
- Who contracted for the ocean transportation or storage?
- Who is identified as consignee or ultimate recipient in the shipping documents?
- Did a freight forwarder or NVOCC issue a separate invoice under its own agreement?
- Does the invoice explain why your business is the billed party?
- Are you being billed once, or are multiple parties being asked to pay the same charge?
If the answer is unclear, ask the billing party for the contractual and shipment-document basis for the charge. For a significant amount, get advice from a maritime- or trade-law professional before making a legal conclusion.
The invoice review: five controls before approval
A good review is faster when every invoice passes through the same sequence.
1. Match the identity of the shipment
The invoice should let you identify the shipment without guessing. At minimum, look for:
- Bill of lading number
- Container number or numbers
- Port of discharge for an import
- The basis for treating your business as the party responsible for the charge
Compare those fields to your freight-forwarder file and receiving records. A single transposed container digit can make an otherwise detailed invoice belong to another shipment.
If the invoice covers several containers, require a line-by-line breakdown. Never approve a lump sum when you cannot tell which containers generated it.
2. Rebuild the free-time calculation
The bill should identify:
- Invoice date
- Due date
- Allowed free time in days
- Start date of free time
- End date of free time
- Actual container availability date for imports
- Earliest return date for exports, when relevant
- Specific date or dates charged
Now compare those dates with your operating evidence. For an import, “vessel arrived” is not automatically the same as “cargo became available.” Check the terminal notice, customs-release status, holds, appointment records, and pickup logs.
For detention, compare the carrier’s dates to the equipment interchange record, drayage appointment, empty-return receipt, and any notice that the terminal or depot was closed or unable to receive equipment.
A useful review asks two separate questions:
- Did the charge start on the correct date?
- Did the business have a realistic opportunity to perform the action that would have stopped the charge?
3. Recalculate the amount
The invoice must show the total amount due, the applicable rule or contract basis, and the specific rate or rates used.
Recalculate the amount with a simple schedule:
charge = chargeable days × daily rateThen test whether the rate changes by day or by threshold. Many tariffs use tiers, so multiplying every day by the first displayed rate can be wrong.
Record the currency, tax or fee treatment, and any credits separately. If an NVOCC adds its own service charge, do not bury that amount inside the carrier’s demurrage or detention line. The underlying carrier charge and the intermediary’s fee have different evidence and dispute paths.
4. Check the dispute instructions
A compliant invoice should identify:
- A contact method for questions or requests for mitigation, refund, or waiver
- A public digital destination—such as a URL or QR code—explaining what documentation the billing party needs
- The deadline for submitting a request
- The timeframe in which the billing party will resolve it
Save a PDF of the invoice and a copy of the dispute instructions when you receive them. Websites and customer portals change; a screenshot or downloaded page can be important if the instructions later disappear.
5. Confirm the required certifications
The invoice should include statements that the charge is consistent with FMC rules and that the billing party’s own performance did not cause or contribute to the underlying charge.
Those statements do not decide every dispute. They do, however, give your review a clear question: what operational event supports the charge, and what evidence shows that the billing party did not create the delay?
Build an evidence packet before the deadline
Do not wait until the last day to reconstruct the shipment. Create a packet for each disputed invoice with:
- Invoice and all attachments
- Bill of lading
- Booking confirmation and service contract or tariff excerpt
- Arrival, availability, and customs-release notices
- Terminal gate hours, closure notices, and appointment records
- Trucking dispatch messages and no-show or rejected-appointment evidence
- Equipment interchange or empty-return receipt
- Emails requesting free-time relief, mitigation, refund, or waiver
- Proof of payment if the business paid under protest
- A short calculation showing the amount you believe is valid and the amount disputed
A clear packet is more persuasive than a long email thread. Put the container number and invoice number in every filename, and keep a one-page timeline at the front.
The FMC specifically identifies invoices, bills of lading, proof of payment, screenshots of denied appointments, gate-closure evidence, and relevant emails as useful supporting documents for a charge complaint. Those are also the records your internal reviewer needs.
Make the accounting entry match the dispute status
Demurrage and detention can affect several parts of your books. A practical chart of accounts might separate:
- Import demurrage expense
- Equipment detention expense
- Freight-forwarder or NVOCC service fees
- Recoverable carrier credits
- Disputed logistics charges
- Inventory or landed-cost allocations, if your accounting policy capitalizes qualifying costs
The exact financial-statement treatment depends on your accounting framework and policy. The operational control is universal: distinguish an accepted charge from a disputed charge.
For example, suppose a carrier invoices $4,800 for a container. Your review supports $1,200 but disputes $3,600 because the availability date appears wrong. Your records should preserve that split:
- Record the payable or expense for the amount you accept.
- Track the disputed amount in a clearly labeled review or dispute schedule.
- Record the request for waiver or refund and its deadline.
- When the carrier issues a credit, tie it to the original invoice rather than recording an unexplained reduction in current-period freight expense.
If the charge is part of inventory cost under your policy, flag the disputed portion before a month-end or year-end close. Otherwise, a later credit can distort gross margin or the cost basis of goods sold.
A plain-text ledger makes this relationship visible. You can link the invoice, container timeline, and dispute message in a transaction narration or supporting-document index, then review every open item with a normal text search. See the Beancount documentation for the underlying ledger approach and Fava for browser-based views of your financial data.
A 30-day dispute workflow
Use the invoice date as the starting point for your internal clock, even if the billing portal displays a different “due” date.
Day 0: Log and acknowledge
Save the original invoice, assign an internal owner, and record:
- Invoice date
- Last date charged
- Dispute-request deadline
- Amount billed
- Container and bill of lading
- Current accounting status
If the invoice is incomplete, write to the billing contact promptly and state that you are requesting the missing information and reserving your position on payment.
Days 1–10: Reconcile
Pull the operational records and rebuild the dates and rates. Ask the freight forwarder for the underlying carrier invoice and a complete breakout of any charges it has passed through. Keep the request in writing.
Days 11–20: Submit the request
Send a concise mitigation, refund, or waiver request. Identify each disputed day, the reason it is disputed, the evidence supporting your position, and the amount you accept, if any.
Do not send only “please waive this.” A reviewer should be able to reproduce your calculation from the packet.
Days 21–30: Escalate and preserve
Confirm receipt and save the acknowledgement. If the billing party has not resolved the matter, follow its published escalation path. Keep the disputed amount visible in your accounts-payable report until the outcome is documented.
If the dispute concerns a charge assessed by a common carrier and you believe it may violate the Shipping Act, the FMC provides a Charge Complaint process. The agency asks for the carrier’s identity, an explanation of the suspected violation, and supporting records. Other disputes may be appropriate for informal assistance or a formal claim, depending on the parties and the remedy sought.
Common mistakes that make valid disputes harder
Paying first and asking questions later
Payment can be commercially necessary to release cargo, but mark the payment as disputed when that is your position and retain proof. A payment record without a dispute record is difficult to interpret months later.
Treating vessel arrival as cargo availability
A container cannot be picked up merely because a vessel arrived. Holds, terminal operations, appointment availability, and actual release status belong in the timeline.
Mixing detention with trucking expense
A drayage invoice, a carrier detention invoice, and a terminal demurrage invoice are different obligations. Separate them so you can identify the responsible party and apply the right contract.
Losing the free-time terms
The number of free days is not always obvious from a commercial invoice. Save the relevant service-contract section, tariff rule, or negotiated arrangement with the shipment file.
Letting the portal become the only record
A customer portal is a delivery channel, not an archive strategy. Download invoices, confirmations, dispute instructions, and final resolutions to storage controlled by your business.
A compact approval checklist
Before approving a demurrage or detention invoice, answer yes to these questions:
- Can I identify the bill of lading, container, and port?
- Does the invoice explain why this business is the billed party?
- Is the invoice within the applicable 30-day issuance window?
- Are the availability, free-time, charged-day, and due-date fields present?
- Can I reproduce the rate calculation?
- Does the invoice identify a real dispute contact and process?
- Does the evidence show that the charge was not caused by the billing party?
- Have I saved the shipment timeline and supporting documents?
- Is the accepted, disputed, or pending amount reflected correctly in the books?
- Is the dispute deadline assigned to a person and calendar?
If any answer is no, pause approval and open a documented exception.
Simplify Your Financial Management
Port-charge disputes are easier when every invoice, timeline, and credit has a visible place in your records. Beancount.io offers plain-text accounting that is transparent, version-controlled, and AI-ready, so your logistics costs and open disputes remain understandable instead of trapped in a black box.