Final September Manheim Index Falls 1.1% as Wholesale Conversion Softens

Conversion and three-year-old values weakened

Cox reported that the Three-Year-Old Index declined 1.7% during September, slightly more than its typical 1.5% depreciation for the period. Average MMR retention was 99.3%, down 0.2 percentage points from August but 0.3 points above the prior year.

Auction sales conversion averaged 55.2%, 1.1 percentage points below August and 1.9 points below the recent three-year September average. Lower conversion can indicate that seller expectations and buyer bids are not clearing as easily, although the national measure does not describe every lane, region or vehicle.

Why it matters

Used-vehicle departments entered October with more evidence that late-summer book values and acquisition targets need review. A national decline does not justify cutting every appraisal by the same percentage, but it does raise the cost of carrying an over-allowance or delaying a retail price decision.

Managers should compare their own 30-, 45- and 60-day inventory against current local transactions. The useful question is not whether the national market fell; it is which models, price bands and powertrains in the store's market are moving differently from the index.

EV and non-EV values moved in opposite directions

Cox's EV index increased 0.6% from August and 4.3% from a year earlier. Its non-EV index fell 1.7% month over month and 1.6% year over year. Compact cars also held up better than midsize cars, pickups and SUVs in the annual comparison.

Those category results are broad averages. Battery condition, incentive changes, model redesigns, lease returns, fuel prices and local demand can produce much larger differences for an individual vehicle. Stores should not substitute a national powertrain index for VIN-specific appraisal evidence.

The year-end forecast was reduced

Cox lowered its forecast for the December index to approximately 0.2% above the prior year, down from the 2% increase projected in July. That remains a forecast, not a guaranteed price path for the fourth quarter.

Wholesale supply ended September at 28 days, down 1.1 days from August but 2.4 days above the prior year. The combination of softer conversion and slightly higher annual supply supports tighter buying discipline without establishing a broad inventory surplus.

What dealerships should do now

Reconcile appraisals, aging reports and recent auction results by model and price band. Review unsold vehicles whose carrying assumptions still rely on August values, and separate market movement from condition or merchandising problems.

For EVs and diesel vehicles, use local supply, battery or mechanical condition and recent comparable sales rather than the national powertrain average. Record the reason for any major appraisal adjustment so the store can evaluate its buying decisions after the vehicle sells.

AI-assisted reporting disclosure

This article was researched and generated with AI-assisted systems using the Cox Automotive sources listed below. Dealership Tech Report applies automated accuracy and risk checks, but the Manheim index remains a proprietary national measure. Confirm local values and current transaction evidence before making inventory decisions.