Check a demurrage or detention invoice against 46 CFR part 541

One invoice

The dates that decide it

Invoice / reference number Date the charge was last incurred required Date the invoice was issued required Date the charge was first incurred

Who billed you

The biller is Billing party name Your company (the billed party) You were billed as Move direction

The invoice itself all optional

Total amount billed Only ever echoed back to you. This page never estimates what you might recover. Daily rate Dates charged Days the invoice allows you to dispute Container number Bill of lading

Required elements — 46 CFR 541.6

Mark each one against the invoice in front of you. If you are not sure, leave it on “not sure” — an unsure answer never counts against the carrier. It goes on a list of things to check on your document.

Anything you can evidence — 46 CFR 545.5 optional

These are reasonableness arguments, not billing defects. They only appear in your letter if you assert them, and each needs evidence you can produce. Leaving one blank neither alleges it nor waives it.

Result

Your 46 CFR 541.8 request letter

Many invoices at once

Point this at a CSV export from your TMS or accounts-payable system. It is read in your browser like everything else — the file is never uploaded. Columns it recognises include invoice_number, invoice_date, charge_last_incurred, container, bill_of_lading, total_due and the rest of the 541.6 elements. A column your export does not have is treated as an element the invoice omits, so check a flagged row against the paper invoice before relying on it.

What this cannot tell you

It reads the face of the invoice only. It cannot check that the free time, daily rate or tariff rule printed on the invoice match your service contract, the terminal schedule or the carrier's filed tariff. That needs your contract, and it is where most substantive overcharges hide.
Present is not the same as true. 541.6 requires each element to be present and accurate. This checks presence. An element that is there but wrong will pass.
It never estimates a recovery. The only money shown is money you typed in.
It is not legal advice and creates no attorney-client relationship. The 30-day windows are read as inclusive of day 30; day 31 is the first late day.
Part 541 covers US import/export ocean moves. Nothing here addresses rail, air, or non-US charges.

What the FMC found in Docket CC-002, and what this checker reproduces →

The rules engine and this page are open source: github.com/maximusrufus/fmc-541-check (Apache-2.0). If the checker misreads a carrier layout, open an issue with a redacted invoice.