Stacked vs. Single-Limit UIM Coverage in Washington

By the FigureMyTax Editorial Team · How we calculate

Stacking adds the underinsured limits of several policies together. Washington's statute lets a policy provide that, with other similar insurance, the total limits cannot exceed the higher of the applicable limits, and that its limit is the maximum for one accident regardless of the number of vehicles or premiums.

What stacking means

A household may have more than one policy with UIM. Stacking adds those limits after one injury, so $100,000 and $50,000 become $150,000. Single-limit coverage pays only the one limit that applies.

What Washington law says

RCW 48.22.030(5) says the policy may define its limit of liability as the maximum for all damages from any one accident regardless of the number of covered persons, claims, vehicles, premiums shown or paid, or vehicles involved. Subsection (6) says the policy may provide that if you have other similar insurance under other policies, the total limits of all coverages shall not exceed the higher of the applicable limits.

What it leaves open

The statute says a policy "may" include those clauses; it does not say what happens if yours does not. We did not read Washington court decisions on stacking, so read your policy for those clauses and ask an attorney.

A worked example

Suppose you have $100,000 and $50,000 of UIM under two policies, the other driver's insurer paid $25,000, and your damages are $250,000. With the higher-limit clause, UIM pays up to $100,000. Without it, it could be up to $150,000. Try your own numbers in the Washington UIM stacking calculator.

What to check

Look at the declarations page and the UIM section of each policy. See what RCW 48.22.030 says and how Washington UIM works.

This is general information, not legal advice, and the state comparisons above are illustrative, not an exhaustive survey. Confirm how Washington's rules apply to your specific case with a licensed Washington attorney.