What it means
The difference sounds technical and is anything but. Under an occurrence policy an incident in 2021 is covered by the 2021 policy even if the claim arrives in 2027, while under a claims-made policy that claim is covered only if you still hold claims-made cover in 2027 and the retroactive date reaches back to 2021.
Let the policy lapse and the historic exposure becomes uninsured. Two features control the coverage window.
The retroactive date is the earliest incident date the policy will respond to, and it should normally be held at the date you first bought continuous cover, since agreeing to advance it in return for a cheaper premium quietly deletes years of protection. The reporting window is the policy year itself, extended only if you buy tail cover.
Tail cover, formally an extended reporting period, lets you report claims after the policy ends for incidents that occurred before it ended. It matters most when a firm is sold, merges or closes, or when a partner retires, because claims can arrive long after the business stops trading.
Insurers usually price it as a percentage of the expiring annual premium, and it is a one-off payment rather than an annual one. Claims-made cover is also cheaper in its early years, which flatters budgets and misleads buyers.
Premiums step up over roughly four years as the retroactive date recedes and the insurer becomes exposed to more historic years, until the policy is described as mature. Comparing a first-year claims-made quote against an occurrence quote is therefore not a like-for-like comparison.
The practical discipline is simple: notify early and notify everything. Most claims-made wordings allow notification of circumstances that might give rise to a claim, which locks the matter into the current policy year even if the formal claim arrives later.
Failing to notify a known circumstance before renewal is one of the most common ways cover is lost entirely.
In practice
Real-world examples
Example 1
An architect retires and closes her practice after 22 years. Because her professional indemnity cover was claims-made, she buys a six-year tail so that a defect claim arising from a building completed in her final year is still covered after the firm has stopped trading.
Example 2
A consultancy switches insurer to save 15% on premium, and the new insurer sets the retroactive date at the inception of the new policy rather than the original one. Eight months later a claim arrives relating to work done three years earlier, and neither the old nor the new policy responds.
Example 3
A hospital group discovers a possible medication error during an internal audit but no patient has complained. Its risk team notifies the circumstance to the current claims-made insurer immediately, so when a claim is filed two years later it attaches to the year of notification rather than falling into a gap.
Think of it
A claims-made policy is like a security guard who only protects your shop if they are actively on duty when a customer complains. If the guard leaves for the day, any complaints that happen afterwards are not covered, even if the issue started while they were watching.
Formula
Calculation
There is no valuation formula, but two arithmetic rules matter. The premium follows a maturity step-up, where each year's premium = mature premium x that year's maturity factor, and tail cover = expiring annual premium x tail factor.
Worked example: an engineering consultancy is quoted a mature claims-made professional indemnity premium of $24,000 a year, against $30,000 a year for equivalent occurrence cover. The insurer's maturity factors are 40% in year one, 70% in year two, 90% in year three and 100% thereafter.
Year 1: $24,000 x 40% = $9,600
Year 2: $24,000 x 70% = $16,800
Year 3: $24,000 x 90% = $21,600
Year 4: $24,000 x 100% = $24,000
Over four years the claims-made route costs $9,600 + $16,800 + $21,600 + $24,000 = $72,000, against $30,000 x 4 = $120,000 for occurrence cover, an apparent saving of $48,000.
The consultancy is then sold at the end of year four and needs a six-year tail priced at 200% of the expiring premium. That costs $24,000 x 200% = $48,000, which exactly erases the $48,000 saving. The real comparison over the full period is $72,000 + $48,000 = $120,000 either way, which is why tail cost belongs in the decision from the start.Case study
Seen in the real world
Denholm Actuarial is an illustrative, fictional advisory firm of eleven partners that carried claims-made professional indemnity cover for fourteen years without incident. When two partners retired and the remaining nine merged the practice into a larger group, the finance partner cancelled the policy on the merger date to avoid paying for cover the firm no longer needed.
Nineteen months later, in this fictional scenario, a former client brought a claim relating to a pension valuation Denholm had signed four years before the merger. The incident sat comfortably after the retroactive date, so it would have been covered had a policy been in force, but there was no live claims-made policy to notify and no tail had been purchased. The acquiring group's own policy excluded prior acts of the acquired firm, and the retired partners faced personal exposure.
A tail at the time of the merger would have cost roughly $61,000 against an expiring premium of $34,000. The defence costs alone in the illustrative claim exceeded $400,000, which is a blunt reminder that the last premium a claims-made buyer pays is usually the most important one.
Watch out
Common mistakes
- Cancelling claims-made cover when a business closes or is sold. Historic work stays exposed for years, and without a tail there is no policy left to notify when a claim finally arrives.
- Letting a new insurer reset the retroactive date. Moving that date forward removes cover for everything you did before it, which is usually a far bigger loss than the premium saving that prompted the switch.
- Waiting for a formal claim before telling the insurer. Most wordings require notification of circumstances that might give rise to a claim, and staying quiet through a renewal can leave the matter uninsured under both policies.
Questions
People also ask
What is the retroactive date and why does it matter?
It is the earliest incident date the policy will respond to, so any work done before it is outside cover no matter when the claim is made.
How much does tail cover usually cost?
Insurers commonly price extended reporting periods at between 100% and 300% of the expiring annual premium depending on the length of the tail, and it is charged once rather than annually.
Why do professional liability insurers prefer claims-made cover?
Because it lets them see and price the exposure year by year rather than committing today to unknown court awards and legal costs decades into the future.