Deductible Rating and Retrospective Rating Plans
How deductible credits are calculated and how retrospective rating plans adjust premiums based on loss experience.
Deductible Rating Fundamentals
Large deductible programs allow commercial insureds to retain a portion of each loss, typically ranging from $1,000 to $250,000 or more per occurrence. The insurer pays the full claim and then bills the insured for the deductible amount (a "billing deductible" structure), or the insured pays losses below the deductible directly. The deductible credit reflects the expected savings from shifting losses below the deductible to the insured. These programs are popular with large commercial accounts that want to retain predictable, manageable losses while transferring catastrophic risk to the insurer.
From the insurer's perspective, a large deductible program reduces expected loss costs but introduces credit risk because the insured must reimburse the insurer for the deductible portion of each claim. Collateral requirements (letters of credit, surety bonds, or trust funds) are typically imposed to mitigate this credit risk. The actuary must price both the expected loss reduction from the deductible and the credit risk associated with the insured's obligation to reimburse.
Loss Elimination Ratios
Actuaries calculate deductible credits using loss elimination ratios (LERs), which measure the proportion of expected losses eliminated by the deductible. The LER at deductible level D equals the limited average severity at D divided by the unlimited average severity. For example, if the average claim severity is $20,000 and the average claim cost capped at a $10,000 deductible is $7,000, the LER is 7,000 divided by 20,000, or 35%. This means 35% of expected losses fall within the deductible, and the deductible credit would be approximately 35% of the base premium (before adjustments).
LERs depend heavily on the severity distribution of the underlying coverage. Lines with many small claims and few large ones (like auto physical damage) will have high LERs at moderate deductible levels because most losses are eliminated. Lines with heavier tails (like general liability) will have lower LERs because a larger proportion of losses exceeds any given deductible. Higher deductibles produce diminishing marginal credits because each incremental layer of retention contains less expected loss than the layer below it.
Retrospective Rating Plans
Retrospective rating adjusts the final premium based on the insured's actual loss experience during the policy period. Unlike guaranteed cost programs where the premium is fixed at inception, retro plans allow the premium to vary within a predetermined range. This approach rewards good experience with lower premiums while capping the insured's exposure through a maximum premium. Retrospective rating is most common in workers compensation and general liability for large accounts.
The standard retro premium formula is: Retro Premium = (Basic Premium + Converted Losses + Excess Loss Premium) multiplied by the Tax Multiplier, subject to the Minimum and Maximum Premium. Each component serves a specific purpose. The basic premium covers the insurer's fixed expenses and the cost of providing the minimum and maximum premium guarantees. Converted losses equal the insured's actual incurred losses multiplied by a loss conversion factor (LCF) that loads for loss adjustment expenses. The excess loss premium charges for losses expected to exceed a per-occurrence loss limit within the plan.
Retro Plan Parameters
The key parameters of a retro plan include the entry ratio (which determines the basic premium as a proportion of standard premium), the loss conversion factor (typically 1.05 to 1.20, covering allocated loss adjustment expenses), the per-occurrence loss limit (capping the contribution of any single claim to converted losses), the minimum premium (the floor, typically 25% to 50% of standard premium), and the maximum premium (the ceiling, typically 100% to 150% of standard premium). The tax multiplier accounts for premium taxes and assessments.
These parameters interact to define the risk-sharing arrangement. A narrow spread between minimum and maximum premiums means the insured bears less risk, but the basic premium will be higher to compensate. A wider spread gives the insured more upside from good experience but also more downside from bad experience. The actuary selects parameters that balance the insured's risk tolerance with the insurer's need for adequate compensation.
Calculating Retro Table Entries
The minimum and maximum premium constraints create an insurance charge and a savings charge. The insurance charge represents the expected cost to the insurer when losses are so high that the retro premium would exceed the maximum (the insurer absorbs the excess). The savings charge represents the expected benefit to the insurer when losses are so low that the retro premium would fall below the minimum (the insurer keeps the difference). These charges are calculated from the expected distribution of aggregate losses and are published in retro rating tables by NCCI and other rating bureaus.
Common Pitfalls
A frequent mistake in deductible rating is applying a deductible credit that does not account for the specific severity distribution of the risk being priced. Using an industry-average LER for a risk with unusual claim characteristics can produce inaccurate credits. Another pitfall is ignoring the credit risk inherent in large deductible programs. If the insured becomes financially unable to reimburse the insurer for deductible amounts, the insurer bears the full cost of claims.
For retro plans, a common error is selecting plan parameters without adequately considering the insured's aggregate loss distribution. If the maximum premium is set too low, the insurer may not collect enough premium to cover adverse loss scenarios. Actuaries should also ensure that the loss conversion factor accurately reflects the relationship between allocated loss adjustment expenses and indemnity for the specific risk.
Study Tips
For exam preparation, practice calculating loss elimination ratios from a given severity distribution. Understand how the deductible credit varies with deductible size and severity distribution shape. Be comfortable with the retro premium formula and know the purpose of each component. Practice calculating retro premiums for different loss scenarios and verify that the minimum and maximum constraints apply correctly. Review how insurance charges and savings charges are derived and how they relate to the aggregate loss distribution. Finally, understand the trade-offs involved in selecting retro plan parameters from both the insured's and insurer's perspectives.