Case Reserves vs. IBNR: What’s the Difference?

Insurance companies maintain liabilities for unpaid claims. These liabilities fall into two broad categories: case reserves, which are established for claims that have already been reported, and IBNR (incurred but not reported), which covers claims that have occurred but haven't yet been reported to the insurer.

Though both appear on the balance sheet as reserves, they are set differently, by different people, using different information. This article explains how each works and how they relate to each other, plus why reserving accuracy matters for insurers.

Quick Comparison: Case Reserves vs IBNR

Case reserves are estimates of the amount an insurer expects to pay on individual claims that have been reported but not yet settled. A claims adjuster or claim handler typically establishes them on a case-by-case basis, using the specific facts of that claim — the nature of the injury, legal exposure, medical prognosis, and any other information available at the time. Case reserves are therefore claim-specific and forward-looking.

IBNR, by contrast, is an estimate of claim dollars outstanding for events that have already happened but have not yet been reported to the insurer. Because the insurer doesn't know which claims will emerge, IBNR cannot be set on a case-by-case basis. Instead, it's estimated in the aggregate using statistical methods that project ultimate losses based on historical patterns.

What Are Case Reserves?

A case reserve is an estimate of the ultimate settlement or adjudication amount for a specific claim that has been reported to the insurer. When a claim comes in, a claims professional reviews the available information: the nature of the loss, policy coverage, potential legal exposure, and any other relevant facts. They then assign a dollar figure representing what the company expects to pay. That figure becomes the case reserve.

Case reserves are dynamic. As new information emerges — medical reports come in, litigation progresses, or settlement negotiations advance — the reserve is adjusted up or down to reflect the updated estimate. In aggregate, case reserves represent a significant portion of an insurer's total liabilities on the balance sheet.

Strengths of Case Reserves

Here are the primary strengths of case reserves:

• Claim-specific: Each reserve reflects the unique facts and circumstances of an individual claim.
• Adjustable: Reserves can be updated as new information becomes available.
• Actionable: Claims staff can manage individual files based on reserve levels.
• Transparent: The basis for each reserve is documented in the claim file.

Limitations of Case Reserves

Here are key limitations of case reserves:

• Subjective: Estimates rely heavily on the judgment and experience of the claim handler.
• Inconsistent: Different adjusters may reserve differently for similar claims.
• Volatile: Reserves can change significantly as claims develop.
• Labor-intensive: Maintaining case reserves on thousands of individual claims requires substantial staff time.

What Is IBNR (Incurred But Not Reported)?

IBNR is a reserve for claims that have occurred but have not yet been reported to the insurance company. Reporting delays arise for many reasons. For example, policyholders may not know they have a claim, medical bills may take time to arrive, or legal claims may take months or years to emerge. IBNR also includes provisions for future development on known claims — sometimes called IBNER (incurred but not enough reported) — though the term "IBNR" is often used broadly to encompass both.

How Case Reserves and IBNR Work Together

Case reserves and IBNR together make up an insurer's total reserve for unpaid claims. They serve different purposes and cover different populations of claims, but they're not independent:

• Distinct coverage: Case reserves cover reported claims. IBNR covers unreported claims and future development on reported claims.
• Combined total: The sum of case reserves and IBNR equals the total carried reserves for unpaid claims.
• Interdependence: Inaccurate case reserves increase the need for IBNR, because the actuary must compensate for under- or over-reserving at the case level.
• Shared data: Actuarial IBNR estimates often rely on incurred loss data that includes case reserves as a component.

How Actuaries Estimate IBNR

Actuaries estimate IBNR using statistical methods applied to historical claims data. The most common approach is the chain ladder method, which uses run-off triangles of paid losses and incurred losses to project ultimate claim amounts. Other methods include the Bornhuetter-Ferguson method, which blends historical development patterns with an a priori estimate of ultimate losses. The completion factor method is another, which estimates what percentage of incurred claims have already been reported.

Key inputs to IBNR estimation include:

• Historical paid loss and incurred loss triangles
• Loss development factors derived from past experience
• Assumptions about future claim reporting and settlement patterns
• Industry data when company-specific data is insufficient

Common Challenges in Claims Reserving

Reserving is never exact, and several challenges make it difficult to get right. Inaccurate or inconsistent case reserving is a common problem. When claim handlers reserve too high or too low, or when reserving practices vary across handlers, the aggregate case reserve becomes unreliable. That unreliability flows through to IBNR estimates that depend on incurred loss data, which includes case reserves.

Insufficient historical data can also undermine reserve accuracy. Statistical methods like chain ladder require several years of credible data to produce reliable projections. Newer lines of business or recently acquired books of business often lack the data depth needed for robust estimates.

Changing claims environments introduce another layer of difficulty. Legal rulings, regulatory changes, medical inflation, and shifts in claims handling practices can all alter loss development patterns. When the past no longer predicts the future, historical methods lose their footing.

Over- and under-reserving risks are the direct consequence of these challenges. Over-reserving ties up capital unnecessarily. Under-reserving leaves the company exposed to unexpected losses that can threaten solvency.

Why Accurate Reserving Matters for Insurers

Reserving accuracy benefits the entire enterprise:

• Solvency and financial health: Reserves are the largest liability on most insurers' balance sheets. If reserves are materially wrong, the company's reported surplus is wrong too. That can mask true financial condition until claims actually develop, sometimes with catastrophic results.
• Regulatory compliance: Insurance regulators require companies to hold adequate reserves. Inaccurate reserves can trigger regulatory action, including financial examinations, increased capital requirements, or even supervision.
• Strategic decision-making: Core strategic functions (from product development to capital management) depend on an accurate view of the company's loss exposure. If reserves are inaccurate, every decision built on them carries added risk.

Accurate Reserving Starts With Lewis & Ellis

Since 1968, Lewis & Ellis has helped insurers across life, health, and property & casualty lines set reserves they can rely on. With over 40 actuaries and offices nationwide, we bring the expertise to tackle complex reserving challenges, from case reserve reviews to IBNR estimation and regulatory compliance.

Contact our team today to learn how we can support your reserving needs.