A damaged car is declared a total loss on financial grounds rather than engineering ones. The decision compares the cost of repair against the value of the vehicle and what its remains are worth.
The comparison is economic, not structural
An insurer's liability is broadly the vehicle's market value immediately before the incident, so any repair costing more than that value is uneconomic by definition.
Salvage value shifts the threshold lower. If the wreck can be sold for parts or resale, the insurer nets that amount, so repair becomes uneconomic well before cost reaches full value.
The consequence is that identical damage produces different outcomes on different cars. An older vehicle is written off by an impact that a newer one would survive commercially.
Repair estimates include more than visible damage
Assessors work from published repair times and parts prices, adding paint, consumables and the labour needed to strip and reassemble panels to reach the damaged area.
Hidden damage is common, and modern vehicles require calibration of cameras, radar and sensors after structural or windscreen work, which adds cost that is invisible on inspection.
Because these additions are substantial, an estimate frequently rises after teardown, and a repair authorised initially can be reclassified as a total loss part way through.
Categories describe what may happen next
Most markets classify write-offs into categories reflecting whether the vehicle may return to the road, may be used only for parts, or must be destroyed entirely.
The distinctions turn on structural damage and safety-critical components rather than on the size of the repair bill that triggered the decision.
Category definitions, their names and the rules attached to them differ by jurisdiction and have been revised over time, so a term used in one country may not translate to another.
A recorded write-off follows the vehicle
Write-offs are recorded against the vehicle identity in registers that buyers and insurers can search, and the record persists after any repair.
A repaired write-off therefore sells for less than an equivalent car without the record, because future buyers face the same disclosure and the same discount.
Insurers may also apply different terms to such vehicles, which is one reason the discount persists rather than fading as the repair recedes into the past.
Valuation is where disputes arise
Because the settlement is based on pre-incident market value, the dispute is usually about that figure rather than about the decision to write the car off.
Owners can present evidence of comparable vehicles advertised locally, documented condition and any specification that raises value above a generic guide figure.
Retaining the salvage is sometimes possible, with the settlement reduced by its value, though whether this is permitted depends on the category and on local rules.