Uninsured motorist insurance and its companion, underinsured motorist coverage, protect you from having to pay for injuries or property damage caused by accidents you did not cause. This coverage is required in some states, but it is also available in others. In most cases, adding to your auto policy will not cost you much money. Here's what else you should know.

How uninsured motorist coverage works

An uninsured motorist is someone who does not have liability car insurance. When you are in an accident and the other driver is at fault, their insurance should cover your car repairs as well as medical expenses for you and your passengers. If the other driver does not have insurance and is unable to pay, you may be stuck with the bill.

When you are in an accident with an uninsured driver, the same thing can happen. Underinsured motorists have insurance, but not enough to cover all of the damage they've caused.

Uninsured/underinsured motorist coverage is intended to bridge the gap between your costs and the ability of the other driver to pay.

What does uninsured motorist coverage pay for?

Uninsured motorist coverage pays for injuries or damages suffered by you, family members in your household, or passengers in your vehicle as a result of an accident caused by an at-fault driver who does not have insurance. Underinsured motorist coverage is similar in that it pays out when the at-fault driver's insurance is insufficient to cover all damages.

Uninsured and underinsured motorist coverage comes in four varieties:

• Uninsured motorist bodily injury, or UMBI, pays for medical bills, pain and suffering, lost wages if you are unable to work as a result of an accident, and funeral expenses if the at-fault driver does not have car insurance. It may also protect you if you are hit while walking or riding your bike.
• Underinsured motorist bodily injury, or UIMBI, covers the same expenses as UMBI, but only in cases where the at-fault driver does not have enough insurance to cover all damages.
• Uninsured motorist property damage, or UMPD, pays for damage to your car or property caused by an at-fault driver who does not have car insurance. A deductible may be required.
• Underinsured motorist property damage, or UIMPD, covers car and property damage after an accident with a minimally insured at-fault driver after you pay your deductible.

If you require additional protection, you should look into full coverage insurance. Although a specific full coverage policy cannot be purchased, this term often refers to a combination of coverages such as comprehensive and collision insurance, as well as any state-mandated coverages such as liability insurance and uninsured and underinsured motorist coverage.

Which states require uninsured motorist coverage?

Uninsured motorist coverage is required in 18 states and the District of Columbia. Car insurance is not required in New Hampshire or Virginia, but if drivers in either state purchase it, policies must include uninsured/underinsured motorist coverage as well as property damage coverage. If you do not want the coverage, you may be required to reject it in writing in other states.

Even if uninsured and underinsured motorist coverage is not required in your state, you may want the added security they provide. According to the most recent data available, roughly 13% of drivers nationwide — or about 1 in 8 — are uninsured, according to a 2017 study by the Insurance Research Council.

Because uninsured motorist coverage may pay out if you are hit by an underinsured driver, it can also be beneficial if you are hit by someone who has only the bare minimum of car insurance. In some states, the minimum liability limit for bodily injury is as low as $15,000; injuries sustained in a car accident can easily exceed that amount.

Use the table below to find out what your state requires for uninsured/underinsured motorist coverage.

The cost of uninsured motorist coverage

Prices for uninsured motorist insurance are relatively low when compared to other types of coverage in an auto policy, but they may be higher in states with a higher percentage of uninsured drivers.

Because liability insurance is designed to protect your assets if you cause a collision, you would want the same financial security if someone else caused the collision. As a result, it is customary to purchase uninsured motorist coverage in amounts at least equal to your liability limits. The more assets you have and the more liability insurance you buy, the higher your uninsured motorist coverage costs are likely to be.

Even so, when purchased in the same amounts, uninsured and underinsured motorist insurance is less expensive than liability coverage — typically less than half the cost.

'Stacked' uninsured motorist coverage

You may be able to "stack" your uninsured motorist coverage depending on your state and insurance company. You can combine uninsured/underinsured motorist bodily injury limits for multiple vehicles — either under one policy or across multiple policies in your name — for an additional fee to increase overall coverage in an accident.

As an example, consider the following: Assume you have two cars covered by a single policy, each with $50,000 in uninsured motorist bodily injury coverage. If you choose to stack the coverage, any injury expenses incurred as a result of an accident with an at-fault uninsured driver will be covered up to the total stacked policy limit of $100,000.