Ocean procurement often stops at the base freight and a few named surcharges. Then the container sits at the terminal — or the chassis sits at your warehouse — and a second bill arrives: detention, demurrage, or both. Those lines are not “gotchas.” They are time-priced equipment charges that belong on the same all-in worksheet as ocean, bunker, and duty.
As of August 26, 2026, this post is operational literacy for shippers and 3PLs — not customs, legal, or carrier-contract advice. Free-time clocks and fee schedules vary by carrier, port, and contract. Always reconfirm the tariff that sits on your booking.
Detention vs demurrage (plain language)
| Term | What it usually prices | Clock starts when… | Who typically pays |
|---|---|---|---|
| Demurrage | Container sitting inside the terminal / CY after free time | Gate-in / availability / discharge free time expires | Shipper / consignee (varies by Incoterm) |
| Detention | Container outgated (on chassis / at facility) after free time | Outgate free time expires | Same — often the party that controls the box |
Many terminals and carriers also use combined free time or local names (storage, CY rent). The principle is the same: calendar days after the free window cost money per day per box.
For glossary definitions that match how we talk about surcharges elsewhere, see the surcharge glossary.
Why demurrage belongs next to the ocean line
A $6,800 Shanghai–LA print looks fine until port dwell stretches free time. Example (illustrative — replace with your carrier tariff):
| Line | Amount |
|---|---|
| Ocean all-in (base + known bunker/PSS) | $6,800 / 40HC |
| Free time at destination | 4 calendar days |
| Expected dwell before pickup | 7 days |
| Excess days | 3 |
| Demurrage | $150 / day × 3 = $450 |
| All-in for this box | $7,250 (+7%) |
Three days of demurrage is a rate move — equivalent to a mid-single-digit spot bump — without any change to Drewry or SCFI.
Detention works the same way after outgate: warehouse delays, appointment shortages, or chassis scarcity convert into $/day until empty return.
Free time is a planning input, not a courtesy
Treat free time like a cutoff:
- Ask for the clock — calendar vs working days; weekends/holidays included?
- Ask for the rate schedule — day 1–4 vs day 5+ step-ups are common.
- Ask who controls the clock — CY availability notification vs physical gate-in.
- Model the dwell you actually expect — not the marketing average.
If your destination port is printing multi-day vessel waits or appointment backlogs (as Shanghai-side congestion did in late August 2026 wraps), bake extra demurrage days into the quote before you commit inventory to that sailing.
A simple all-in stack that includes time
Use the landed-cost worksheet for duty math you already know, and add a time block beside freight:
| Block | Include |
|---|---|
| Ocean | Base + named surcharges on the quote |
| Fuel / emergency | BAF, EFS, WRS if on the invoice |
| Time | Expected demurrage days × schedule + expected detention days × schedule |
| Accessorials | Chassis, exam, reefer plugs (if any) |
| Duty | Your known HTS % — do not invent classification here |
Rule of thumb: if time risk exceeds 5% of ocean, print it as a separate line on the internal quote so sales and ops see the same number.
What load planning has to do with detention
Detention often starts because the warehouse cannot strip fast enough. Mixed-SKU loads without a clear door-first sequence, overweight axle surprises, or missing VGM paperwork all burn free time after outgate.
Before you chase another carton into the cube:
- Confirm strip sequence matches warehouse labor capacity.
- Confirm weight distribution will not fail road limits at the gate.
- Confirm empty return appointments are available in the free window.
Compare two packing scenarios when a denser plan adds a day of strip time — the cheaper ocean print can lose to detention.
Checklist before you accept the “all-in”
| Check | Pass if… |
|---|---|
| Free time (origin + destination) | Written on quote or contract schedule |
| Demurrage / detention rates | Day tiers known |
| Expected dwell | Modeled ≥ realistic port/warehouse days |
| Incoterms | Clear who pays demurrage vs detention |
| Strip plan | Labor + sequence match free window |
| Empty return | Appointment capacity checked |
Bottom line
Ocean indexes do not price your free-time miss. Detention and demurrage are part of the freight product. Put them on the same quote as the box rate, stress-test dwell, and only then decide whether the sailing is “cheap.”
Next step: run your SKUs through the Palletizr calculator so the strip plan matches the free window you just modeled.