"Stacked" coverage increases the limits on your uninsured motorist bodily injury coverage if you have multiple cars. Your UM limits typically cannot be higher than those on your liability coverage, but if you have two cars and stack your limits, your coverage is effectively doubled. It is cheaper to get more protection against uninsured motorists without buying higher liability limits for yourself. Stacking will increase your premium, but not by as much as higher liability limits would. Not all states allow stacked coverage.