Demurrage vs. Container Detention, Port Storage, and Chassis Fees

Demurrage generally means a container is still inside the port or terminal past the allowed free time. Container Detention — also called Per Diem — generally means a container has left the terminal but hasn't been returned on time. Port/Terminal Storage is a charge for occupying yard space. Chassis Fee relates to using, repositioning, or holding onto a chassis too long. None of these are the same thing as Driver Detention, which is the charge for a driver and truck waiting too long at a pickup or delivery site. The specific free time, when it starts, how it's billed, and who's responsible depend on the ocean carrier, terminal, rail ramp, chassis provider, and the contract in place.

Why "port storage fees" doesn't cover everything

Shippers often lump every port-related late fee together as "demurrage" or "storage," but containers and equipment can run late at different points in the supply chain, and each point has a different name, a different billing party, and a different point of responsibility. A container still sitting in the terminal is demurrage. A container that left the terminal but hasn't been returned empty is container detention / per diem. Occupying yard space is storage. Using or repositioning a chassis is a chassis fee. And a driver waiting at a warehouse or delivery point is an entirely separate charge — driver detention. Treating these as interchangeable makes it easy to dispute the wrong charge with the wrong evidence.

What is Demurrage?

Demurrage is the charge for a container remaining inside the port or terminal beyond the free time allowed by the ocean carrier or terminal. The point of responsibility is "the container wasn't picked up in time." Ocean carriers typically set their own free time period and billing structure in the bill of lading terms, and these rules differ by carrier, port, and commodity type — hazmat and reefer containers, for example, are often treated differently.

What is Container Detention / Per Diem?

Container Detention — often called Per Diem in rail and chassis-interchange contexts — is the charge for a container that has already left the terminal but wasn't returned empty within the allowed free time. The point of responsibility is "the equipment wasn't returned in time." Under the Uniform Intermodal Interchange and Facilities Access Agreement (UIIA), administered by IANA, free time generally begins the business day following interchange and excludes Saturdays, Sundays, and holidays; once free time runs out, detention/per diem is billed for every calendar day — including weekends and holidays — until the equipment is returned to the provider.

What is Port/Terminal Storage?

Storage is what a terminal or designated facility charges for occupying yard space with cargo or equipment, and it's typically billed separately from demurrage — though the two can stack. A container that's past its demurrage free time and still sitting at the terminal may generate both demurrage and storage at the same time. The exact billing structure depends on that terminal's own tariff.

What are Chassis Fee, Chassis Split, and Chassis Detention?

Chassis Fee covers the cost of using a chassis — rental, maintenance, and related charges. Chassis Split refers to the extra dispatch cost when the container and chassis aren't available at the same location and have to be matched up separately. Chassis Detention is the charge for holding a chassis past its allowed free time; the billing logic resembles container detention, but the billing party is the chassis provider, not the ocean carrier or terminal. The UIIA, administered by IANA, is currently the main U.S. industry agreement governing chassis and equipment interchange across most equipment providers and motor carriers.

Why Driver Detention is yet another, separate charge

Driver Detention is the charge for a driver and truck waiting too long — beyond the agreed or allowed time — at a pickup or delivery site such as a warehouse, terminal, or receiving dock. It happens on the drayage leg, and it's usually billed by the trucking company that actually performed that move. It's a completely separate line item from the demurrage an ocean carrier bills or the chassis detention a chassis provider bills — different point of responsibility, different billing party, different evidence required. Don't treat it as the same fee.

When does Free Time start?

Different stages of the process calculate free time differently. Container demurrage free time generally starts at a point agreed between the ocean carrier and terminal after discharge, and most ports calculate it in calendar days — but the exact rule depends on that carrier's and terminal's current tariff. Under the UIIA framework, chassis/container detention free time starts the business day after equipment interchange, excluding Saturdays, Sundays, and holidays — and once that free time is used up, billing switches to every calendar day, including weekends and holidays. These are two different calculation methods and shouldn't be applied interchangeably.

What timing, appointment, and release issues eat into Free Time

• Customs release or freight release (from the carrier or forwarder) not completed in time
• No pickup appointment available at the terminal, or the appointment gets pushed back
• Drayage and warehouse unloading schedules not coordinated before the last free day
• No confirmation in advance that the return location accepts that carrier's or that size of empty container
• Chassis shortages preventing pickup on schedule

A delay at any one of these points can mean the container or chassis isn't picked up, unloaded, or returned before free time runs out — which is what generates demurrage, detention, or storage.

Who can actually issue these invoices?

Worth repeating: ocean carriers, terminals, rail ramps, chassis providers, and ports don't share one set of rules. This article doesn't fix a specific free-time period in days, and doesn't promise weekends or holidays are excluded — check the contract and tariff that actually applies to your move.

For ocean carrier and marine terminal demurrage and detention specifically, 46 CFR §541.6 (effective May 28, 2024) sets federal requirements for what must appear on the invoice — including the container number, the dates used to calculate free time, the applicable rate, and the billing and billed parties — and requires vessel-operating carriers and terminal operators to issue the invoice within 30 calendar days of when the charge was incurred (NVOCCs have 30 days from receiving their own invoice). An invoice missing required elements doesn't have to be paid. This rule governs ocean carrier/terminal demurrage and detention — it doesn't cover drayage-side fees like chassis or driver detention.

How importers, forwarders, warehouses, and drayage carriers typically split responsibility

In practice, demurrage is usually billed by the ocean carrier or terminal to the bill-of-lading holder (or their designated forwarder). Container and chassis detention are usually billed by the equipment provider, under UIIA rules, to the trucking company responsible for the equipment interchange — which then settles with the cargo owner per their own contract. Storage is billed by the terminal or warehouse to whoever is occupying the space. Who ultimately absorbs each of these costs depends on the service agreements between the parties — it's worth nailing this down at quote and contract time, before a charge shows up and everyone points at someone else.

Pre-pickup checklist

• Ocean carrier name, Bill of Lading number, container number
• Available date
• Last free day (demurrage free-time deadline)
• Whether customs release and freight release are both complete
• Whether a terminal pickup appointment is confirmed, and the time window
• Warehouse address, unloading plan, delivery window
• Return location and requirements (does it accept that carrier's / that size of empty container?)
• Chassis source and availability

What records to keep when a charge is disputed

• Bill of lading, and proof of customs/freight release (screenshots or confirmation emails)
• Last free day notice and appointment confirmation
• Timestamps for pickup and return, along with signed receipts
• The terminal's or chassis provider's itemized invoice and the rule it cites
• Where applicable, check the invoice against the minimum-information requirements set out in 46 CFR Part 541

Summary

Demurrage, Container Detention, Port Storage, Chassis Fee, and Driver Detention are five distinct charges from five different points in the port-and-drayage chain, with different billing parties — they can't be summed up as a single "port storage fee," and there's no single industry-wide free-time period or fixed dollar amount. The Federal Maritime Commission's 2024 rule is currently the only charge in this group with actual federal regulatory backing — it sets minimum disclosure and invoicing-timeline requirements for ocean carrier and terminal demurrage/detention billing. Chassis interchange, by contrast, runs primarily on the UIIA industry agreement administered by IANA. The best way to cut down on disputes is to nail down who's responsible for what in advance, record the key timestamps accurately, and check every invoice line against the rule that actually applies to it.

Before arranging a U.S. port pickup, send us the ocean carrier, terminal, container number, available date, last free day, appointment status, customs release, freight release, warehouse address, unloading plan, and return location. ShipMay can help you coordinate the drayage, transload, and downstream legs, but the specific charges are still governed by the current rules of whichever service provider is involved. Start a quote.

Related reading

• Drayage vs. Transloading: what's next after your container arrives?
• Los Angeles drayage guide: pickup, delivery, and common delays
• Detention, Layover, TONU, Redelivery: What's the Difference?
• A complete guide to U.S. freight accessorial charges
• Port drayage
• Transloading

Sources

• Federal Maritime Commission (FMC) — official summary of the Demurrage and Detention Billing Requirements final rule
• Federal Register — 46 CFR Part 541, full rule text
• IANA — Uniform Intermodal Interchange and Facilities Access Agreement (UIIA), the industry agreement governing chassis and container interchange
• Port of Los Angeles, official site, for port free-time and demurrage rules
• Port of Long Beach, official site