How UIM Offset Calculations Work in Illinois
Mon 23 Feb, 2026 / by Robert Parker / Uninsured / Underinsured Motorist Claims
How UIM Offset Calculations Work in Illinois
One of the most misunderstood aspects of underinsured motorist coverage is the offset. Many policyholders assume their UIM limits stack on top of the at-fault driver’s liability limits — that if the at-fault driver has $50,000 in coverage and you have $100,000 in UIM, your total available recovery is $150,000. That is usually wrong. Most Illinois UIM policies use a setoff provision that reduces your UIM recovery by the amount you collected from the at-fault driver.
This article is part of our complete guide to UM/UIM claims in Illinois.
The Standard UIM Setoff
Under a standard setoff provision, your UIM insurer pays only the difference between your UIM limits and the at-fault driver’s liability limits — not your full UIM limits on top of the at-fault driver’s payment.
Example: You have $100,000 in UIM coverage. The at-fault driver has $50,000 in liability coverage. Your UIM insurer owes you a maximum of $50,000 ($100,000 minus $50,000 setoff) — not $100,000. Your total maximum recovery from both sources is $100,000, not $150,000.
When this matters most: If your UIM limits equal the at-fault driver’s limits, the setoff reduces your UIM recovery to zero. If you carry $50,000 UIM and the at-fault driver has $50,000 liability, you get nothing from your own UIM policy even though you paid premiums for that coverage.
Why Higher UIM Limits Matter
This is exactly why we tell clients to carry UIM limits well above the state minimum. A $250,000 or $500,000 UIM policy provides a meaningful recovery even after the setoff. The premium difference between $50,000 and $250,000 in UIM coverage is typically modest — often just $50-100 per year — but the difference in protection is enormous.
Exceptions and Variations
Not all policies use the standard setoff. Some policies pay UIM benefits on a “damages minus liability” basis rather than a “limits minus limits” basis. Under this approach, the insurer calculates your total damages, subtracts what you received from the at-fault driver, and pays the remainder up to your UIM limits. This is generally more favorable to you.
Additionally, if you can stack your UIM coverage across multiple vehicles, the stacked total is compared against the at-fault driver’s limits for the setoff calculation — which can significantly increase your recovery.
Settlement Coordination
Before settling with the at-fault driver’s insurer, always notify your UIM carrier. Most UIM policies require you to get your insurer’s consent before accepting a settlement from the at-fault driver. If you settle without consent, your UIM insurer may argue you prejudiced their subrogation rights and deny your UIM claim entirely.
Frequently Asked Questions
Does my UIM coverage stack on top of the at-fault driver’s insurance?
Usually not. Most Illinois UIM policies have a setoff provision that reduces your UIM recovery by the amount of the at-fault driver’s liability coverage. Your total recovery is typically capped at your UIM limits, not the sum of both policies.
What if my UIM limits are the same as the at-fault driver’s limits?
Under a standard setoff, you would receive nothing from your UIM coverage. This is why carrying higher UIM limits than the state minimum is important — it ensures your UIM coverage actually provides additional recovery.
Do I need my insurer’s permission before settling with the at-fault driver?
Yes. Most UIM policies require you to notify your insurer and obtain consent before accepting a settlement from the at-fault driver. Settling without consent can jeopardize your UIM claim.
Talk to a Peoria UM/UIM Attorney
Call (309) 672-9000 or contact us online for a free consultation. At Parker & Parker Attorneys at Law, we handle UM/UIM claims on a contingency fee basis — you pay nothing unless we recover compensation for you.
If you were injured by a driver without adequate insurance, the experienced Peoria personal injury lawyers can help you explore all available options.
Need a lawyer? This article is part of our Peoria Uninsured Motorist Lawyer practice area. Call Parker & Parker at 309-673-0069 for a free consultation.