Kentucky's UIM works on top of the other driver's limits, and stacking turns on how you were charged
Kentucky's rules are in KRS 304.39-320 (underinsured coverage and settlement notice) and 304.20-020 (uninsured coverage and rejection). The no-fault threshold is in 304.39-060, the minimum limits in 304.39-110 and the tort deadline in 304.39-230.
Read how stacked and single-limit coverage differ in Kentucky, check what the statutes say and leave open, or see how UM and UIM work under Kentucky no-fault.