Detention Rounding Increments: Recompute the Billing

Detention rounding increments decide more of your detention billing than the hourly rate does. A carrier billing hourly with any part of an hour rounded up collects a full hour for six extra minutes. The same load billed in 15-minute increments collects a quarter of that. Same dwell, same rate, same contract clause about free time, and a bill that differs by 45 minutes of detention on a single stop.

The recompute is simple arithmetic, and almost nobody does it, because the invoice presents a whole number of hours and whole numbers look like facts. What they really are is the output of a rounding convention that the invoice usually does not state, applied in an order of operations the invoice never states.

This post shows the three conventions, the order-of-operations trap that costs the most money, and how to recompute a detention line from raw timestamps in about two minutes.

The answer first: what actually governs the rounding

Nothing in federal regulation sets a detention rounding increment for domestic motor carriage. There is no rule that says quarter hours, no rule that says round up, no rule that says round at all. It is contractual, and it lives in one of three places:

1. The rate confirmation, if it is specific (most are not).
2. The transportation agreement or broker-carrier agreement.
3. The carrier’s rules tariff or accessorial schedule, incorporated by reference into one of the above.

If none of those three states an increment, then the carrier has applied a convention you never agreed to, and the honest position is that the elapsed time should be billed as it was actually measured. That is a reasonable dispute to raise, and it is a very reasonable clause to fix at renewal.

What regulation gives you is the right to see the arithmetic. Under 49 CFR 373.103, a freight or expense bill must show the exact rates assessed and the total charges due with the nature and amount of each charge. A line reading “DETENTION 300.00” states an amount but not its nature: no hours, no rate, no start or stop time. Asking for the hours, the rate and the rounding applied is a request with a rule behind it, and it is the right first move before you argue anything about merits.

The three conventions, and what each does to the same dwell

Take one stop. Free time is two hours. Detention is $75 per hour. The truck was on the property for 3 hours 6 minutes, so the chargeable dwell past free time is 1 hour 6 minutes.

Six minutes of dwell produced a $67.50 spread. On one stop that is noise. On a lane running 40 detention events a month, the convention alone is the difference between roughly $6,000 and roughly $3,300 a year in this illustration, before anyone argues about a single timestamp.

Note the direction of the error. All three conventions are defensible business practices, and rounding up on a started increment is not sharp practice: a carrier whose driver sat six extra minutes did lose six minutes it cannot resell. But the rounding is one-directional. Nobody rounds down. So a rounding convention applied to a stream of loads is a systematic transfer, not a wash, and the size of that transfer is set entirely by the increment size.

The order-of-operations trap

This is the expensive one, and it is invisible on the invoice.

There are two ways to combine free time and rounding, and they produce different numbers:

Order A, subtract then round. Total dwell, minus free time, then round the remainder up to the increment. Order B, round then subtract. Round the total dwell up to the increment, then subtract free time.

On a 3 hour 6 minute dwell with two hours free and hourly rounding, Order A gives 1:06 rounded up to 2 hours. Order B gives 3:06 rounded up to 4 hours, minus 2 free, which is also 2 hours. Same answer, so far.

Now change the dwell to 4 hours 2 minutes with two hours free:

• Order A: 4:02 minus 2:00 = 2:02, rounded up to 3 hours. $225.
• Order B: 4:02 rounded up to 5:00, minus 2:00 = 3 hours. $225.

Still the same. The divergence appears when free time is not a whole increment, which is common. Free time of 90 minutes, hourly rounding, dwell of 3 hours 10 minutes:

• Order A: 3:10 minus 1:30 = 1:40, rounded up to 2 hours. $150.
• Order B: 3:10 rounded up to 4:00, minus 1:30 = 2:30, and with a second rounding, 3 hours. $225.

A 50 percent difference on identical facts, from an ordering nobody wrote down. Order A is the reading most people assume and the one most rate confirmations imply, because free time is described as time you do not pay for. Order B effectively charges for part of the free time. If a carrier’s number is materially higher than yours and the timestamps agree, order of operations is the first place to look.

Freight invoices are full of this class of error: two operations that commute in the easy cases and diverge in the real ones. The same trap shows up in linehaul pricing, where discount and fuel can be applied in either sequence, worked through in the order of operations on a freight invoice.

The other modifiers that change the arithmetic

Rounding is one of five settings. Any of them can be present, and each one changes the number without changing the rate.

Minimum charge. “Detention billed at $75/hr, two-hour minimum once free time expires.” One minute past free time becomes $150. This is not rounding, it is a floor, and it is the single largest driver of surprise detention amounts on short overages.

Daily cap or maximum. “Detention capped at $500 per 24-hour period.” A cap helps you and it is worth knowing you have one, because carriers do not always apply their own caps correctly on multi-day dwell.

Increment after the first hour. Some schedules bill the first hour whole and then move to quarter hours. Two conventions on one charge, and the invoice shows a single number.

Per-stop versus per-load. On a multi-stop load, free time may be allocated per stop or pooled across the load. Pooled free time on a two-stop load with an hour of dwell at each is often zero detention. Per-stop free time on the same load is also often zero. But a carrier applying free time once and then billing both stops is a real error worth catching.

After-hours and weekend rates. A different rate for detention accruing outside standard hours, which means a dwell that crosses 5 p.m. has two rate segments and the invoice shows one blended number.

How to recompute a detention line in two minutes

You need four inputs. Three of them come off documents you already have.

1. Start and stop timestamps. From the POD, gate log, guard sign-in, appointment record, or the carrier’s own detention worksheet. If the POD is blank, reconstruct from what exists: the approach for that is in disputing a detention charge with no POD times, and the fuller evidence set is in the documents that win a detention dispute.
2. The clock trigger. Which event starts free time, per the agreement. This is upstream of all the arithmetic and it is where most disputes actually live: see when detention free time actually starts. If the timestamps themselves are contested between an ELD trace and a driver’s entry, reconcile that first using ELD dwell against driver-entered arrival times.
3. Free time and the rate. From the rate confirmation or accessorial schedule.
4. The rounding increment, the minimum, and the order. This is the input that is usually missing. If the documents do not state it, that absence is your dispute.

Then:

• Compute raw dwell: stop minus start.
• Subtract free time. If the result is zero or negative, there is no detention, regardless of what the invoice says.
• Round the remainder up to the stated increment. If no increment is stated, do not round.
• Apply any minimum, then any cap.
• Multiply by the rate. Compare to the invoice.

If your number and the carrier’s number differ, the difference will almost always be one of four things: a different trigger, a different stop time, an undisclosed minimum, or Order B.

A worked reconciliation

Illustrative. Free time two hours, rate $75/hr, quarter-hour increments stated in the accessorial schedule, no minimum.

Four loads, $281.25 of difference, and only one of the four (load C, billed detention on a stop that never exceeded free time) is an error anyone would call obvious. The other three are the carrier applying hourly rounding to an agreement that says quarter-hour. That is rarely fraud. Much more often it is a billing system configured with a default that nobody reconciled against this specific contract, which is what most detention overbilling turns out to be.

The dispute writes itself from that table: the contract says quarter-hour increments, here are four loads billed hourly, here is the arithmetic, please issue corrected invoices. A table beats a paragraph every time, because it lets the carrier’s billing team verify your claim without recomputing anything.

What to say, and what not to say

Say: the accessorial schedule states 15-minute increments, the invoice reflects whole-hour rounding, and the difference on these loads is $X. Ask for a corrected invoice and release the undisputed balance.

Say: the invoice does not state hours, rate, or rounding, and 49 CFR 373.103 requires the nature and amount of each charge, so please itemize before we process.

Do not say: that rounding up is improper. It is a normal commercial convention and it is defensible when the contract states it.

Do not say: that a regulation caps detention or sets the increment. Nothing does, for domestic truckload, and the claim will be corrected by someone on the carrier side who knows.

Do not treat a small delta as a reason to skip payment on the rest of the invoice. Pay the undisputed portion. It keeps the relationship intact and removes any past-due leverage while the corrected invoice is prepared.

Timing matters on both sides. Under 49 U.S.C. 13710, a carrier must bill charges additional to those originally billed within 180 days of your receipt of the original bill to preserve its collection rights, and you must contest a bill within 180 days of receipt to preserve your right to challenge. If you already paid, this is an overcharge claim rather than a dispute, and under 49 CFR 378.8 the processing carrier must pay, decline, or settle a written overcharge claim within 60 days of receipt absent a written agreement to extend. The rest of these clocks are collected in the freight billing deadlines reference.

Fix it at the contract, not on the invoice

Recomputing detention line by line is worth doing once, to size the problem. It is a bad permanent habit. The permanent fix is four sentences in the accessorial schedule.

Language worth having, written so that both sides can compute the same number:

• The increment. “Detention is billed in 15-minute increments, with any partial increment rounded up.”
• The order. “Free time is subtracted from total elapsed time before rounding is applied.”
• The minimum, or its absence. “No minimum detention charge applies,” or state the minimum plainly if one is agreed.
• The evidence. “Detention claims must be supported by arrival and departure timestamps from the facility record or signed delivery receipt.”

That last one mirrors what practitioners already treat as the minimum record set before a detention charge is contested: the rate confirmation with the free-time and clock language, the BOL or POD with facility timestamps, and the carrier’s own detention documentation. It is the clause that pays for itself, because it moves the burden to the point where the evidence is cheap to capture. A carrier that knows a claim needs timestamps attached usually attaches them.

Detention rounding is a small number that repeats. That is exactly the profile of the errors worth systematizing: not dramatic on any one bill, meaningful across a year, and completely invisible unless somebody recomputes.

The checklist

1. Find the stated increment. Rate confirmation, transportation agreement, then rules tariff. If it is not stated anywhere, note that.
2. Find the stated minimum and any daily cap.
3. Determine the order: is free time subtracted before rounding, or after.
4. Pull start and stop timestamps and confirm the trigger they represent matches the contract.
5. Recompute: dwell, minus free time, rounded up to the increment, then minimum and cap, then rate.
6. Compare against the invoice and isolate the cause of any difference.
7. Sample ten detention invoices from the last quarter before disputing one. A pattern is far more persuasive than a single load.
8. Put the increment, the order, the minimum and the evidence requirement into the accessorial schedule at renewal.

Sources

• 49 CFR 373.103, What a freight or expense bill must show (Cornell LII)
• 49 U.S.C. 13710, Billing and contesting windows (Cornell LII)
• 49 CFR 378.8, Overcharge claims resolved within 60 days (Cornell LII)
• Detention as a standard accessorial in practitioner taxonomy (Zipline Logistics)
• Documents needed before contesting a detention charge (Laneproof)
• DOT OIG Report ST2018019, Driver detention economics (U.S. DOT Office of Inspector General)