The shape of depreciation

Ask how fast a truck loses value and the honest answer has three parts: a normal rate, a curve that flattens, and a cliff. Miss any one and the valuation is wrong for a whole cohort of trucks.

The normal rate

In a year without a shock, J.D. Power puts monthly depreciation, the average fall in selling price from one month to the next for a fixed group of benchmark trucks, at about 2 percent for three-to-five-year-old sleepers at retail. It called 2.2 percent a month for 2024 "historically typical." At auction, four-to-six-year-old sleepers ran 0.8 percent a month in 2024 and 1.8 to 2.2 percent through 2025. FleetOwner's September 2026 guide gives dealers' rule of thumb as 1.5 to 2 percent a month. In the bad months of 2023 the figure was closer to 6 percent, three times normal, and in late 2021 it was negative: trucks appreciated 7 percent a month at auction.

The curve

Two percent a month compounds into a steep ladder in the early years and flattens later. J.D. Power's December 2025 edition, the last to print dollar figures, gives the ladder directly for its benchmark sleeper.

Read down the auction column and the curve is visible: 58,800 to 44,000 to 37,200 to 24,100 to 21,900. The first three steps are large; the last is small. After five or six years a truck has shed most of what it will shed, and its price is set by remaining life and condition more than by the calendar. ACT Research's Steve Tam frames the whole curve with one number: used pricing "runs in a very tight band of about 30 to 35 percent of the new truck price." PACCAR Financial, which has to guess these values years ahead when it writes a lease, sets its residuals between 30 and 60 percent of original cost.

The cliff

Age is only half the story because a truck can be four years old with 300,000 miles or with 600,000. Somewhere around 400,000 miles and four years, a tractor stops being a substitute for a new one, still under factory warranty and inside its first engine life, and becomes a maintenance project priced on what is left. J.D. Power spent 2025 observing that "lower-mileage trucks remain scarce and continue to bring premium money." An independent dealer described the old rule of thumb to FleetOwner this month as "4 years old, 400,000 miles, 40,000 dollars," and added that "that benchmark is gone": in a scarce market, clean trucks of that vintage bring 5,000 to 10,000 dollar premiums.

At the far end there is a second flattening. Price Digests states its policy plainly: a base on-highway truck "typically lasts about 10 years before a major component is replaced or the odometer flips," and after that point "mileage adjustments have a negligible impact on the used value." Past ten years, a truck is priced on what has been rebuilt, not on what the odometer says.

Depreciation is a slope in year one, a curve by year three, a cliff at 400,000 miles, and a plateau after year ten. One rate cannot describe it.