How to audit freight invoices: carrier and accessorial charges

For shippers, brokers and 3PLs of roughly 20 to 200 people in the US, a carrier invoice can look right and still be wrong. The linehaul matches the quote, the total is close to what the lane usually costs, and a line for detention or a lumper fee sits near the bottom with nothing attached to it. Accounts payable (AP) approves it because nothing obviously fails, while the evidence sits in a gate log and a scanned proof of delivery.

What does a freight invoice audit involve?

A freight invoice audit, often called a freight audit, is the comparison of a carrier's bill with the agreement and the shipment records behind it, to confirm you are paying the agreed rate for the service that was delivered. The reference document depends on how the freight moved: the rate confirmation (the document that records the agreed rate and terms for one load) for brokered truckload, the contract or tariff for less-than-truckload (LTL), and the accepted quote where one exists.

Timing splits audits into two kinds. A pre-payment audit runs before AP approves the invoice, so an overcharge is corrected instead of recovered. A post-payment audit reviews invoices already paid, looking for duplicates, uncontracted charges and unsupported accessorials, and then asks the carrier for a credit. Pre-payment is the better place to do the work. Post-payment catches what slipped through, while the dispute window is open.

How long do you have to dispute a freight bill?

In the US, a shipper has 180 days from receipt of a motor carrier bill to contest it, and a separate credit rule sets when the bill is due. These are the US motor carrier rules that matter for the audit clock:

Your contracts may set their own terms, so confirm with counsel which clock applies. Start a contest clock for every invoice on the day it is received, and set an internal filing date well inside the 180 days.

How do you audit a freight invoice step by step?

Audit one invoice in six steps:

1. Match the invoice to the load by PRO number, BOL number or load number, and confirm you tendered that shipment.
2. Compare the base rate, minimum charge and discount with the rate confirmation or contract.
3. Check the fuel surcharge against the agreed fuel table and the correct week.
4. Check each accessorial, such as detention, lumper, liftgate or truck ordered not used, against the tender, the BOL notes, the POD times and any receipt.
5. Check for duplicates by comparing carrier, PRO number, BOL number and amount with earlier invoices.
6. Route every exception to its owner with a deadline, and hold payment on the disputed lines.

Which fields must match when you audit a freight invoice?

Most freight overcharges hide in a handful of places. Run these comparisons first.

The National Motor Freight Classification (NMFC) class is the freight class LTL carriers use to rate a shipment, so a changed class or weight changes the charge. The fuel surcharge deserves its own check because it moves every week. The U.S. Energy Information Administration states that it "does not calculate, assess, or regulate diesel fuel surcharges", that they are "negotiated privately by shippers and by transportation companies", and that many shippers and carriers use its weekly retail diesel price in their formulas (EIA). The audit question is whether the carrier applied your agreed table to the right week.

A charge you cannot tie to anything is a charge you can ask about. Section 13710 requires a motor carrier of property to provide, on request, "a written or electronic copy of the rate, classification, rules, and practices, upon which any rate applicable to its shipment or agreed to between the shipper and carrier is based."

Where do freight audit documents and rate data come from?

An audit pulls from at least four places, and they rarely sit together. The invoice arrives as a PDF in the AP inbox or a carrier portal, or as an EDI 210 message. SPS Commerce describes the EDI 210 as the transaction a carrier sends to a shipper "to request payment of freight charges", typically one per shipment, with segments for the invoice number and payment terms (B3), reference numbers such as the purchase order (N9), dates (G62), line-item weights, rates and charges (LX and L1) and the invoice total (TDS) (SPS Commerce).

The rate confirmation lives in the TMS or in the email thread where the load was booked. The BOL and the proof of delivery (POD) come back as scans or photos from the carrier, the driver or the warehouse. Detention evidence sits with the dock: gate logs, appointment times and the receiver's signature times. Reading a PDF invoice is a document processing problem, covered in AI document processing for invoices, contracts and forms, and the delivery paperwork is the set discussed in shipping document verification.

How can AI automate a freight invoice audit?

A workflow can pick up each invoice as it arrives, match it to the load by PRO, BOL or load number, and read it into a common set of fields: lines, charges, weights and dates. It then compares those fields with the rate confirmation or contract in the TMS, the POD and BOL in your document store, and the carrier's earlier invoices, applying the tolerances you set. Each charge ends in one of three states: supported, mismatched with both values shown, or unsupported because the evidence is missing.

AI earns its place in the reading and the writing. It can extract a line-item table from a scanned invoice, recognize that "DET", "Detention" and "Wait time" are the same charge, read arrival and departure times off a POD photo and pull the amount from a lumper receipt. The comparison itself is ordinary arithmetic and rules, which keeps it easy to audit. Duplicates surface by matching carrier, PRO number, BOL number and amount across invoices, even under a new invoice number.

The last step is drafting and timekeeping. For each exception the workflow can prepare a dispute note that names the line, the billed amount, the agreed amount and the attached evidence, ready for an analyst to review and send. It can also run a clock for every invoice from its date of receipt, so nothing ages out of its contest window unnoticed.

Who should receive each exception?

Route by the kind of problem, to the person who can resolve it, with a deadline tied to a date that matters.

1. Accounts payable: places the hold on any invoice with an open exception and tracks the payment due date against the credit terms in the contract or the 15 day default. The hold has to be in place before that due date.
2. Transportation or freight analyst: owns rate, fuel and accessorial disputes with the carrier, with the rate confirmation and evidence attached. Set an internal filing date well inside the 180 day contest window, so the right to contest is never at risk.
3. Operations or dock supervisor: confirms what happened at the door, including arrival and departure times, whether a lumper was requested and who signed. Ask for an answer within one business day, while gate logs are fresh.
4. Procurement: owns gaps in the rate agreement itself, such as a lane with no rate, an accessorial the contract does not define or an out of date fuel table. The deadline is the next rate review, or sooner if the gap repeats on the next invoice.
5. Finance: handles accruals for disputed amounts, GL coding corrections and month-end cutoffs, on the close calendar.

A mismatch found before payment costs a phone call, while the same mismatch found after the 180 day contest window may no longer be disputable. Invoice matching on the AP side, including receiving records, is covered in three-way match automation.

Which freight audit decisions should stay with a person?

A freight audit prepares a decision about money and a relationship, and it should not make the decisions that bind the company.

Dispute, short pay or accept. Every exception has a commercial cost. A small difference on a carrier that covers a hard lane every week may not be worth a dispute, while a repeated detention charge probably is. A named analyst weighs the amount, the relationship and the contract.

Negotiating with carriers. Disputes involve rate history, capacity and goodwill, which a workflow cannot weigh.

Approving payment. The person with authority under your payment policy approves the invoice. The workflow records the evidence behind the decision.

Changing rate agreements. Procurement decides whether a recurring accessorial becomes a contracted rate.

Loss and damage claims. Cargo claims are a separate process with their own documents and deadlines. The audit can flag a shortage or damage noted on the POD so it reaches the claims owner.

Legal interpretation. Which dispute window or contract term governs a given carrier or broker is a question for counsel.

Illustrative example: Consider a food distributor that books brokered truckload freight through its TMS. For one load, the rate confirmation shows $1,650 linehaul, a $240 fuel surcharge from the agreed table and two hours of free time at each stop. The carrier's PDF invoice bills $1,650 linehaul, $240 fuel, $225 detention and a $150 lumper fee, for $2,265 in total. A workflow ties the invoice to the load by PRO number and finds that linehaul and fuel match. The POD shows arrival at 8:10 and departure at 9:05, inside the free time, and no lumper receipt is attached. AP places a hold and the contest clock starts from the invoice receipt date. The freight analyst asks the carrier for the receipt and disputes the $225 detention with the POD times attached. The analyst decides to pay the $1,890 that is supported inside terms and leave the other two lines open.

How do you know freight invoice audit automation is working?

Judge the audit by the money and disputes it protects, not by how many invoices it processes.

Overcharges caught before payment, against those recovered after shows whether the audit sits in the right place.

Disputes filed inside the contest window tracks how many valid disputes were filed in time, and how many were still open as the 180 days approached.

Duplicates stopped counts repeat bills caught before payment.

Accessorials paid without supporting evidence should fall for detention, lumper and layover charges. It is the clearest sign that the evidence step is working.

Days from invoice receipt to approval shows whether exceptions are routed or sitting in an inbox.

Pull a baseline from the last few months of paid invoices before you start.

How do you start automating freight invoice audits?

1. Choose one freight mode and one group of carriers, for example brokered truckload from your busiest carriers, with enough volume to measure.
2. List the checks your AP team and freight analysts run by hand today, and agree which mismatches are hard stops (a duplicate, an uncontracted accessorial, a charge with no evidence) and which are tolerances (a small fuel rounding difference, for instance).
3. Gather a sample of real invoices with their rate confirmations, BOLs and PODs, including the messy ones and some that are already paid, to test reading accuracy and see what the manual process missed.
4. Let the workflow and your analysts audit the same invoices for a set period, then compare what each one caught.
5. Add routing, deadlines and drafted dispute notes once the findings hold up, and name the owner of each exception type.
6. Extend to LTL, accessorial heavy lanes or a post-payment look-back only when the first group is stable. How to rank candidates is covered in Which business processes to automate first.

How Kastling approaches freight invoice audits

Kastling treats an invoice audit as a workflow to understand before anything is built, as part of the AI Integration & Automation service. It starts with a free discovery call. A separately scoped paid audit is common next for logistics teams, reviewing the carrier invoices you receive, where rate agreements and shipment records live, and where overcharges and late disputes cost money today.

The checks connect to the TMS, ERP and AP tools you already use. Comparison rules are agreed with the analysts who handle disputes, exceptions go to named owners, and the decisions to dispute, short pay or approve stay with your people. We agree up front how success will be measured and test the workflow on your real invoices before it touches live payments.