Black Book's latest Used Vehicle Retention Index for June (115) shows a 0.6% increase from May (114.4), which reflects an incremental improvement in used vehicle values.

Analysts said the strong spring season continued into the first month of summer with majority of segments strengthening in June. Full-size vans (up 1.43%) and premium sports cars (1.25%) performed exceptionally well.

"The uptick in the seasonally adjusted index shows that the strength of the used-vehicle values is steady," said Anil Goyal, executive vice president of operations. "The strength is broadly seen across all mainstream vehicle segments, while luxury brand segments registered a decline."

The index is calculated using Black Book’s published wholesale average value on two- to six-year-old used vehicles, as percent of original typically equipped MSRP. It is weighted based on registration volume and adjusted for seasonality, vehicle age, mileage, and condition.