Uninsured and underinsured motorist coverage
A coverage on your own policy that pays when the at-fault driver carries no insurance, or not enough.
Collision Bureau is not a law firm and this is not legal or medical advice. It is general information about what happens after a crash. For advice on your situation, talk to an attorney licensed in your state or a treating clinician.
What it means
Uninsured motorist coverage, usually written as UM, is the part of your own policy that pays when the driver who caused the crash has no insurance. Underinsured motorist coverage, written as UIM, is the part that pays when the at-fault driver has insurance but the limits do not cover the full file. Together, these coverages exist for the common situation in which the other side cannot pay for the losses it caused. The payer in both cases is your own insurer, not the other driver's.
How it works
The mechanism is a claim against your own policy that borrows the structure of a liability claim. Your insurer stands in the shoes of the missing or inadequate policy, within the limits you bought. Notice goes out early, the file assembles through the same records a liability claim would use, and the resolution runs through the same kinds of conversations. In many states UIM only applies after the at-fault policy's limits have been exhausted, which means the sequence of events matters. Any resolution against your own carrier generally has to account for the subrogation interests of any coverage that paid earlier, including PIP and MedPay.
Why it comes up
It comes up when a crash file hits a wall. The other driver's policy limit is lower than the losses, or there is no policy at all. Without UM or UIM, the claim stops where the at-fault coverage stops. With it, the claim continues into a second phase against your own insurer, up to the limit on your own policy. The point to understand before any crash is that this coverage sits on your declarations page or it does not, and the number next to it is the ceiling. The National Association of Insurance Commissioners keeps consumer material on auto coverages that can help with the vocabulary before you look.
What it is not
UM and UIM are not liability coverage, and they are not a payment from the at-fault driver's insurer. They are coverages on your own policy that convert your carrier into the payer when the other side cannot. They are also not the same as collision coverage, which pays to repair your car regardless of fault but has nothing to say about injuries. Property damage from an uninsured driver generally lives under collision rather than UM. Which pieces apply to your file, and in what order, is a question for the insurer handling the claim and, when the dollars warrant it, a licensed attorney in your state.
Questions people actually ask
01What is the difference between UM and UIM?
UM applies when the at-fault driver carries no insurance at all, including a hit and run in states that treat it that way. UIM applies when the at-fault driver has insurance but the limits are not enough to cover the losses the file supports. Many policies carry the two together as a combined coverage. Which specific flavor applies to your claim is a question for the insurer and, when it is contested, for an attorney in your state.
02Does using UM or UIM raise my premium?
In general terms, no. These coverages exist precisely for a crash that was not your fault, and insurers treat not-at-fault claims differently from at-fault claims. Specific policy and state rules vary. The practical point is that leaving the coverage unused when the other driver cannot cover the losses is often the costlier choice. What makes sense for your file is a question for a licensed attorney in your state, with your declarations page in front of them.
03How does UM or UIM interact with the at-fault driver's policy?
UIM generally pays the gap between the at-fault policy limits and the full value of the file, up to your own UIM limit. UM steps in when the other side has no policy at all. The sequence runs through notice, exhaustion of the at-fault limits where applicable, and then a claim against your own carrier. The specifics are set by state law and policy language, and the order is not a question to improvise. An attorney walks it with you.