Compact SUVs held the strongest retention value in April, increasing 2.8 percent in a month that saw overall depreciation largely unchanged from March levels, according to Black Book.

Overall vehicle depreciation has fallen 12.7 percent from a year ago to an average of $18,997. Domestic vehicle outperformed import vehicles with domestic trucks rising 1.5 percent to $20,891 during the month.

Five truck categories retained their value most during the month, including compact SUVs, full-size pickups (2.5 percent to $27,578), full-size SUVs (1.8 percent to $24,966), sub-compact SUVs (1.7 percent to $21,700) and minivan wagons (1.1 percent to $16,806).

Upper mid-size cars recorded the strongest retention among car categories, increasing 1 percent to $13,180 on average.

The flat month showed the last vestiges of spring tax buyers, according to Anil Goyal, Black Book's vice president of automotive valuation and analytics.

"The fact that we're looking at overall unchanged depreciation levels across used vehicle segments in late April is a testament to the stretched spring season we've had this year," Goyal said. "Looking ahead, it will be interesting to see if the remainder of the year will outperform market expectations."