What it means
The accident year is normally the calendar year, starting on 1 January. A loss belongs to the year it happens, not the year it is reported or paid, and premiums are counted as earned during that same period regardless of when the policies were written.
That matching is the whole point. Insurance claims can take years to report and settle, so comparing this year's premium income with this year's claim payments mixes several vintages of risk into one muddled figure.
Insurers therefore track each accident year separately as it develops, and actuaries revisit earlier years as late claims arrive and estimates harden. The measure drives real decisions.
Pricing teams use it to set next year's rates, reserving teams use it to hold enough capital, and regulators and rating agencies read it as a report card on underwriting discipline. Loss adjustment expenses, meaning the legal fees and adjuster time spent investigating and settling claims, belong inside the figure.
It has two cousins. Policy year experience groups results by the date each policy began, and calendar year figures simply total whatever was earned and incurred within the accounting year.
Each answers a different question, and mixing them up produces misleading comparisons. The measure also exposes management stories.
A company can flatter current results by releasing reserves from old accident years, so analysts watch whether prior-year development is consistently favourable or is masking weak new business. A recent accident year also needs time before it can be judged, since many claims are still unreported.
A loss ratio above 100% means premiums failed to cover losses and expenses, which is an alarm bell for anyone reading an insurer's results. Reinsurers, investors and brokers all watch the same number for the same reason.
In practice
Real-world examples.
Example
A storm-heavy year gives a property insurer a poor accident year ratio, even though most of the claim payments trickle out over the following three years.
Example
An actuary at a motor insurer revises the prior accident year's incurred losses upward as late-reported injury claims arrive.
Example
A reinsurer prices a treaty using the ceding company's last five accident years and not its calendar-year cash results. This gives the reinsurer a fairer view of the risk that the insurer actually kept.
Formula
Calculation
Accident year loss ratio = (incurred losses + loss adjustment expenses for losses occurring in the year) / earned premium for the year x 100
Worked example: an insurer earns $10,000,000 of premium in the year. Losses from that year comprise $4,500,000 paid, $1,500,000 of case reserves for known claims and $800,000 estimated for claims not yet reported, so incurred losses are $4,500,000 + $1,500,000 + $800,000 = $6,800,000.
Adding $700,000 of loss adjustment expenses gives $7,500,000, so the ratio is $7,500,000 / $10,000,000 x 100 = 75%. A year later, late-reported claims lift incurred losses to $7,300,000, so the ratio is ($7,300,000 + $700,000) / $10,000,000 x 100 = 80%, which is why each accident year is revisited as it develops. The same year can therefore look better or worse over time without any new policies being written.Case study
Seen in the real world.
This case study is fictional and illustrative. A finance analyst at Meridian Motor Mutual, an invented regional motor insurer, is asked why the company lost money despite a profitable-looking December report. She rebuilds the numbers by accident year and finds that the calendar view looks fine only because old claims are being paid slowly.
The newest accident year includes a ride-share segment with $4,000,000 of earned premium and $4,600,000 of incurred losses and expenses, a loss ratio of 115%. Pricing raises rates on that segment, underwriting tightens acceptance rules, and two years later that accident year still shows the scar while newer years recover.
Her internal packs now show the vintage view beside the cash view, with a one-line bridge between them. The analyst also asks the claims team for a quarterly update on late-reported claims so that the newest year is not judged too soon. The illustrative company now reviews each accident year at 12, 24 and 36 months.
Watch out
Common mistakes.
- Reading calendar-year cash figures as underwriting performance, when late-developing claims make that view misleading.
- Mixing up accident year and policy year, which group risk differently and answer different pricing questions.
- Judging a recent accident year too early, before claims have had time to be reported and developed.
Questions
People also ask.
Why not just use the calendar year?
Insurance losses lag, so a fire in December may be reported in March and settled two years later, and accident year experience restores the match between risk taken and price charged.
Who uses this measure?
Pricing and reserving actuaries, reinsurers, analysts and regulators use it to judge whether underwriting is disciplined.
What counts as a good result?
A sustained loss ratio below 100% suggests premiums covered losses and expenses, before investment income is considered, although the right target varies by line of business. Lines with long settlement times need more caution because late claims can change the picture.
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