New on FinoLib · Volume III: Finance Encyclopedia
I have added a new article to FinoLib, my finance education website: Insurance Underwriting and Loss Reserving Explained, part of Volume III: Finance Encyclopedia. This page gives you the core of the topic in expert but plain language; the full article goes much deeper.
1.4 Reserving — Provisioning for Claims Not Yet Paid
The idea in plain words
When an insurer sells a policy, it doesn’t yet know what it will owe, so it sets money aside, called reserves. Case reserves cover claims already reported. IBNR, short for incurred but not reported, covers losses that have happened but have not been reported or fully valued. Actuaries estimate these by tracing how claims developed in past years using loss triangles, with methods like the chain ladder, cross-checked by Bornhuetter-Ferguson. Every dollar change in reserves changes pre-tax profit by a dollar.
Key points
■In the worked triangle, chain-ladder IBNR is 44.47 on reported losses of 252.8, and 72% of it sits in the newest accident year.
■Bornhuetter-Ferguson replaces the volatile latest-year projection with an expected loss ratio, cutting 2025’s ultimate from 84.01 to 73.05.
■Broad IBNR includes development on known claims (IBNER), reopened claims and claims in transit.
A closer look
An insurer’s single largest liability on its balance sheet is its claims reserve — money set aside for claims that have already happened (or are expected to happen on already-sold policies) but haven’t yet been fully paid out. Reserving splits into two distinct categories: case reserves (a specific estimate for a known, already-reported claim still being processed) and IBNR — Incurred But Not Reported — reserves for claims that have already happened but haven’t yet even been reported to the insurer, estimated using historical patterns of reporting delay.
Decision rule
If an accident year’s cumulative factor to ultimate is below roughly 1.2 and claims handling has not changed, then rely on the chain ladder. If it exceeds roughly 1.5, then weight Bornhuetter-Ferguson, because the chain ladder multiplies noise. Always run at least two methods, on paid and reported data; when they differ by more than about 10%, find the cause before booking. These thresholds are practitioner heuristics, not rules from a standard. When reading accounts, treat several consecutive years of adverse development as evidence that current reserves are light too.
The costliest mistake
Assuming the tail is finished. The triangle uses a tail factor of 1.000. If the true tail is 1.05, every ultimate is 5% short: 297.27 × 5% = 14.86 of missing reserve, so booked IBNR of 44.47 should have been a third higher (14.86 ÷ 44.47 = 33%). Those 14.86 were reported as profit and return later as an adverse development charge. Tails can be very long: Berkshire Hathaway’s 2024 shareholder letter says it is still making substantial payments on asbestos exposures that occurred 50 or more years ago.
1.5 Underwriting — Selecting and Pricing Individual Risk
The idea in plain words
Pricing sets a price for a group; underwriting applies it to one applicant at a time, deciding whether to accept, charge more or decline. It exists to stop adverse selection: if higher-risk people buy the most and the price is based on the average, the pool gets worse, prices must rise, and healthier customers leave, in what is called a death spiral. Moral hazard is different: it is the change in behavior after people are insured. That is handled with deductibles, coinsurance and claim controls.
Key points
■In the worked pool, a single $3,600 price drives out low-risk buyers and leaves a $128,000 loss on the 20 high-risk ones.
■Risk classes priced at each group’s own expected cost keep low-risk buyers in the pool.
■A $1,000 deductible and 20% coinsurance split a $5,000 claim $1,800 to the insured and $3,200 to the insurer.
Decision rule
If buyers choose whether and how much to buy, and can see something about their risk that your rating variables miss, then assume takers are worse than the population average: rate on observable drivers, require medical evidence or waiting periods for large amounts, and track take-up by segment. If coverage is automatic for a whole group (employer group life, compulsory auto liability), then selection is weak and lighter underwriting is defensible.
The costliest mistake
Pricing on the population average when buyers select themselves. The $3,600 price above was right for a pool that never forms. If only the 20 high-risk applicants buy, claims of 20 × $10,000 = $200,000 meet premium of 20 × $3,600 = $72,000: a $128,000 loss, 178% of premium. Price from the expected mix of actual buyers, check early claims by segment, and underwrite the drivers buyers know best.
What the full article covers
In the full article I take you through these sections:
■1.4 Reserving — Provisioning for Claims Not Yet Paid
■1.5 Underwriting — Selecting and Pricing Individual Risk
It includes worked examples, a look under the hood at the mechanics, a clear decision rule, the one mistake that costs people the most, a recap, a reveal-on-click quiz and the official sources behind every figure.
Volume III: Finance Encyclopedia
Read the full article on FinoLib
The complete article, Insurance Underwriting and Loss Reserving Explained, with every worked example, diagram, quiz and source, is free to read in Volume III, Finance Encyclopedia on finolib.com.
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