Guide
Documenting a supplement so it reads as evidence
A supplement is a second document, not a second opinion. It succeeds on the same terms the first estimate did: specific lines, sourced parts, and a reason attached to each one. The corpus is unusually clear about which column is worth arguing.
Last reviewed . Every figure below is read from the measured corpus at build time, so it moves when the corpus does.
A real supplement, in the carrier's own ledger
$1,333.27
added to an original allowance of $7,668.92
One document. It is published as an illustration of a ledger, not as a typical supplement size, because one is not a sample.
The column that did not move
$56.00
identical across 59 Progressive documents
Body, refinish and frame at the same figure on 45 of 59 documents. Where it moves it moves on supplement: one document shows body going from $52.00 to $95.00 between the original estimate and Supplement 1.
Arguing the right column
The rate on a carrier estimate is closer to a constant than most shops treat it as. Progressive printed the same body rate on 59 separate documents, and printed it identically for refinish, frame and glass on the same documents. Hours and parts are where a supplement has room to work, and they are also where the evidence lives: an hour is defensible with a procedure and a part is defensible with a number. A rate is defensible with nothing except a conversation somebody already had.
The rate is not a constant everywhere, and that matters too
The counterexample is on this site. On the 2024 Ferrari Purosangue, Auto-Owners Insurance allowed $125.00 an hour on body and paint, which is what that shop charges a direct customer, and the two estimates finished about one percent apart on the repair itself. That is one document against the volume carriers' many, and it is the reason this site does not describe its central rate figure as a market rate. What holds is that the high-volume carriers hold their number. What does not hold is that every carrier does.
What actually gets added at teardown
The components that turn up on supplements are the ones a photograph could never have reached. In this corpus they are also the ones adjusters replaced without exception once they were visible, which is the useful half: the supplement is not arguing whether the part is repairable, it is establishing that the part is there and damaged.
| Component | Replaced | Decisions |
|---|---|---|
| radiator/condenser | 100% | 55 |
| bumper impact bar | 96% | 25 |
| fender liner | 100% | 24 |
| bumper absorber | 100% | 20 |
The record the first shoot leaves
Once the cover is off, the condition the car arrived in exists only in the photographs. That is the single cheapest piece of supplement evidence there is and it has to be created before the work starts, which is the only reason it gets missed. Six weeks later, in an argument about whether a bracket was already bent, the first shoot is the only thing in the file nobody disputes.
- Photograph the intact assembly before anything is removed, including the fasteners
- Photograph the concealed component in place, before it comes out, with the surrounding structure in frame
- Note the operation that revealed it. "Found on removal of bumper cover" is a different sentence from "additional damage"
- Put the part number on the added line. A supplement line without one invites the same conversation twice
Not every gap is a disagreement
Two documents can differ by thousands and agree about the car completely. On the 2024 Ferrari Purosangue the shop and the carrier were about one percent apart on labor and parts, and the printed totals still differed by $2,314.26. All of it was fee and tax structure: the shop applies EPA and shop-supply percentages and a single tax rate, the carrier books paint supplies per unit and applies tiered tax. Writing that gap up as a supplement would have been arguing accounting under the heading of damage, and it would have cost credibility on the lines that were real.
The supplements worth preventing
A supplement for hidden damage is the process working. A supplement for something that was visible in the first frame and never got written is the first estimate failing, and it is expensive twice: once in cycle time and once in how carefully the next document from that shop gets read.
- A part number right for the model and wrong for the trim
- A blend into the adjacent panel, never written
- One-time fasteners, clips and seals, left off as though they were free
- A calibration the vehicle requires after a windshield or a bumper is disturbed
How this was measured
- The supplement figure is transcribed from a carrier estimate of record published as a case study on this site, with the vehicle identified by year, make and model only and no claim number, VIN or date of loss.
- Labor rates come from the rate table each carrier prints on its own estimate, with the document count beside each figure so a rate seen once is visibly seen once.
- Concealed-component replace rates come from 912 adjuster repair-or-replace decisions, aggregate only, with panels seen fewer than 6 times excluded.
- Only the shop that assembled this corpus has its own jobs published as case studies. No customer shop's estimates are published, sold, or used as examples.
What this page cannot tell you
Published for the same reason the sample sizes are. A guide that never names its own limits is asking to be trusted rather than checked.
- One published supplement is one document. Nothing on this page is a typical supplement size, a typical supplement rate, or a claim about how often supplements are approved. None of those has been measured.
- The corpus contains carrier estimates and supplements, not the correspondence around them. Whether a given line was argued, conceded or ignored is not in the data.
- There is no measurement here of whether better documentation improves approval. It is the working belief of every estimator asked and it remains untested by this corpus.
- Rate findings rest on 89 documents across 8 carriers collected in one market, and one of those carriers appears once. Treat the consistency as the finding and the level as local.
Before you ask
Is it worth arguing the labor rate on a supplement?
On this evidence, rarely. The deepest sample in the corpus is 59 documents from one carrier printing the same rate on nearly every one, across four labor categories. It is near-flat rather than flat, and the exceptions all sit on supplements. Hours and parts are still where a supplement has the most evidence to bring.
What makes a supplement line survive review?
The same things that make an original line survive it. A specific description of the failure, a part number where a part is involved, a photograph taken at the moment the damage became visible, and the operation that revealed it. Round numbers and vague descriptions are what draw the pen.
Does a longer estimate get approved less often?
A longer estimate gets read more carefully, which is not the same problem. Specific, sourced, priced lines survive a careful reading. Omitting a defensible line to look reasonable gives the line away for nothing, because a line that was never written cannot be paid.
Should the first estimate include an allowance for hidden damage?
Not as an invented line. Note where hidden damage is likely and price it when it is found. This corpus shows concealed components being replaced almost without exception once they are exposed, which is a good argument for looking and a poor one for guessing.
Check the evidence
Nothing on this page is worth more than what it rests on. These are the pages the figures came from.
The data
Carrier labor rates, measured
The rate analysis behind the column a supplement cannot move.
A real repair
2017 Porsche 718 Boxster S, Progressive
The transcribed ledger, including the second claim on the same vehicle.
Written for
For independent body shops
Supplements, rate discipline and what it costs to try this.
Related
Why estimates come back
The avoidable supplements, and what to capture on the first pass.
Run it on damage you have already written
Accounts are created by hand, usually within a business day. Bring your own photographs and a repair order you have already closed, so you can see how close it lands before you decide. No card, no trial timer.