How a Depreciation Curve Is Built

A vehicle's value does not decline at a fixed percentage every single year despite how often that shorthand gets repeated in casual conversation. Depreciation curves are built from real resale transaction data and vary significantly by model, condition, and the broader market conditions in place at the time of a given resale.

This piece covers how these curves are actually constructed from underlying data, who builds and publishes them, and why a single flat rule of thumb does not describe most individual vehicles accurately.

How the Curve Is Modeled

Valuation firms build depreciation curves by aggregating actual sale prices for specific vehicle models across different mileage bands and age brackets, then fitting a statistical curve to that observed data rather than assuming a shape for it in advance of collecting the numbers.

The steepest depreciation for most vehicles occurs in the first one to two years of ownership, after which the rate of decline typically slows considerably, producing a genuine curve rather than a straight line — a vehicle rarely loses the same dollar amount of value in year five that it lost in year one, even if the percentage decline were somehow similar between those two years.

A curve is typically rebuilt on a recurring basis rather than fixed once and left unchanged, since new transactions keep arriving and market conditions for a given model can shift meaningfully within a single year, particularly during periods of unusual supply or demand for that vehicle segment, which is why a curve pulled several years apart for the same model can look meaningfully different from one pull to the next.

Seasonal patterns also feed into the model in a smaller way — certain vehicle types sell at somewhat different price points depending on the time of year, which a well-built curve accounts for rather than averaging away entirely.

Who Publishes These Figures

Independent valuation firms compile this underlying data from auction results, dealer trade-in reports, and private-party sale listings collected across a wide geographic footprint, then publish estimated values that lenders, insurers, and dealerships all reference when a figure is needed for a specific vehicle.

No single party controls the curve itself; it reflects an aggregate of many real transactions rather than a figure set unilaterally by any one company, which is part of why different valuation firms can publish somewhat different figures for the same vehicle depending on which transactions fed into each firm's underlying dataset that quarter.

Where a Flat Estimate Breaks Down

A commonly repeated estimate that a vehicle loses a fixed percentage of its value every year does not hold consistently across models — some vehicles retain value well past what the average curve would predict, while others depreciate noticeably faster than average due to reliability reputation, fuel type, or a shift in broader market demand for that segment.

Applying a flat, averaged estimate to one specific vehicle can significantly misstate its real resale value in either direction, which is why a genuine model-specific curve is a meaningfully different and more useful tool than a rule-of-thumb percentage repeated across every vehicle regardless of make or model or condition.

A vehicle with an unusually strong reliability reputation can hold value well past the point where the average curve for its broader class would predict, which is why a model-specific curve, rather than a class-wide average, is the more accurate tool for estimating any single vehicle's likely resale trajectory.

What a Valuation Report Actually Shows

A valuation report for a specific vehicle typically shows a range of values rather than a single flat number, reflecting differences in condition, mileage, and regional market variation, along with a description of the data window the estimate was built from.

The width of that range is itself informative on its own terms — a wide range indicates more market variability for that particular vehicle than a narrow range would, which is useful context a single-number estimate would otherwise hide entirely from whoever is reading the report.

The curve is built from real, ongoing transactions, which means it moves as the market itself moves, rather than following a fixed schedule fixed in advance and applied uniformly to every vehicle regardless of what is actually happening in that segment of the market. A curve pulled recently will reflect current conditions more accurately than one carried forward unchanged from an earlier valuation cycle.

Note: This explains how a process works. It is not financial or legal advice, it is not specific to any vehicle or lender, and terms vary by state, lender, and dealership. Check the cited sources before making a purchase decision.