8.5 Contribution

What Is Contribution?

Contribution is the principle that where two or more insurers cover the same subject matter, the same interest, and the same risk, they must share the loss between them so that the insured cannot recover more than once. Like subrogation, contribution is a corollary of indemnity: it prevents the insured from recovering more than their actual loss by collecting in full from each of two (or more) policies.

For contribution to apply, the two (or more) policies must cover the same subject matter (the same property or interest), the same insurable interest (the insured's recognised legal relationship with that subject matter), and the same risk (the same peril causing the loss). If any of those three elements differs, there is no contribution between the policies — they respond to different exposures.

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Contribution vs Subrogation

Both are corollaries of indemnity and both prevent over-recovery, but they operate in different directions and the exam will test the distinction:

Subrogation is about holding the wrongdoer liable; contribution is about sharing the cost among insurers who have each accepted the same risk.

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Double Insurance and Contribution

Double insurance describes the situation where the same subject matter, interest, and risk is insured under two or more separate policies, each of which would respond to the loss. The insured may claim from either insurer, but cannot recover twice. The insurer that pays the claim then has a right of contribution against the other insurer(s) for their share.

This is distinct from co-insurance, in which two or more insurers agree from inception to cover the same risk in defined shares under a single arrangement (often with a single policy and a leading insurer). In co-insurance, the shares are agreed up front and there is no need for a separate contribution calculation — each co-insurer simply pays their agreed share. Contribution, by contrast, arises after the loss when separate policies independently respond.

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The Independent Legal Right of Each Insurer

Each insurer under a double-insurance arrangement has an independent legal right to deal with the insured under its own policy. The insured may choose which insurer to claim against in the first instance (typically the one whose policy is most favourable on excess, basis of cover, or claims service). The paying insurer then seeks contribution from the other insurer(s) for their share of the loss.

Because the right of contribution arises between insurers, the insured is not normally involved in the contribution calculation. The insured simply recovers their loss (once) from the policy they chose to claim under, and the insurers sort out the apportionment between themselves.

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Methods of Sharing the Loss

There are three recognised methods of calculating each insurer's contribution. The method used depends on the policy wording (some policies specify the method) and, in the absence of an agreed method, the courts apply the most equitable default.

1. Rateable Proportion (the most common approach)

Under the rateable proportion method, each insurer pays in proportion to the amount they insured (the sum insured under their policy). The formula for each insurer's share is:

Each insurer's payment = (That insurer's sum insured ÷ Total sums insured) × Loss

This is the default method used in most general insurance contexts and is the method the IF1 exam expects unless a different method is specified.

2. Maximum Liability Method

Under the maximum liability method, each insurer pays in equal shares up to the lowest policy limit, with any excess falling on the insurer(s) whose limit has not yet been reached. The sharing is by equal first pounds up to the smallest policy limit, not by proportion. This method tends to favour the insurer with the larger sum insured on small losses (because they share equally up to the smaller limit) and can produce a less intuitive apportionment on large losses.

3. Independent Liability Method

Under the independent liability method, each insurer calculates what it would have paid if it were the only insurer covering the loss (its standalone liability under its own policy, applying any average or limits). The contribution is then shared in proportion to those independent liabilities. This method is more complex and is used in specific contexts (for example, in some marine and professional indemnity arrangements) where the rateable proportion method would not produce an equitable result.

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Worked Example — Rateable Proportion

A business insures its stock under two separate policies: Policy A with a sum insured of £50,000, and Policy B with a sum insured of £100,000. Both policies cover the same stock, the same interest, and the same risk. A fire causes a loss of £30,000. Using the rateable proportion method:

• Total sums insured = £50,000 + £100,000 = £150,000.
• Policy A share = (£50,000 ÷ £150,000) × £30,000 = £10,000.
• Policy B share = (£100,000 ÷ £150,000) × £30,000 = £20,000.
• Total paid to the insured = £10,000 + £20,000 = £30,000 — the full loss, with no over-recovery.

The insured could have claimed the full £30,000 from either policy, and the paying insurer would then have pursued the other for its rateable proportion.

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Worked Example — Maximum Liability Method (Illustrative)

Using the same facts (£50,000 and £100,000 sums insured, £30,000 loss), the maximum liability method produces the same result because the loss is below both policy limits: each insurer pays an equal share of £15,000. Note that this differs from the rateable proportion result (£10,000 and £20,000), illustrating that the method chosen materially affects the apportionment. The maximum liability method produces equal sharing only up to the lower policy limit, and any loss above that limit falls on the higher-limit insurer alone.

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When There Is No Contribution

Contribution does not arise in the following situations, and the IF1 exam may test these exclusions:

• Different subject matter. Policy A covers the building, Policy B covers the contents — no contribution between them on a single loss.
• Different interest. Policy A covers the owner's interest, Policy B covers the mortgagee's interest — the interests are different, even if the subject matter is the same.
• Different risk. Policy A covers fire, Policy B covers theft — a fire loss triggers only Policy A, and there is no contribution from Policy B.
• Life insurance. Because life policies are valued (benefit) policies rather than contracts of indemnity, contribution does not apply in the same way — the insured may hold multiple life policies and recover under each. The corollaries of indemnity, including contribution, apply to indemnity contracts.

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Key Takeaways

• Contribution is the principle that where two or more insurers cover the same subject matter, the same interest, and the same risk, they share the loss so the insured cannot recover more than once.
• It is a corollary of indemnity and is distinct from subrogation, which is recovery against a third party wrongdoer rather than a sharing between co-insurers.
• The most common method of sharing is the rateable proportion method: each insurer pays in proportion to its sum insured, (sum insured ÷ total sums insured) × loss.
• The maximum liability method shares equally up to the lowest policy limit; the independent liability method shares in proportion to what each insurer would have paid acting alone.
• Double insurance (two separate policies on the same risk) triggers contribution, whereas co-insurance is a single arrangement from inception with agreed shares and no separate contribution calculation.